Medical Pressure Sensor Applications in 2021

Medical Pressure Sensor Applications in 2021

Numerous medical devices now depend upon steady and precise pressure measurements so as to run dependably. What’s further, patient care is broadening beyond the gp and the healthcare facility’s surgical treatment and getting here in patients’ houses, such as house health tracking.Because of this, establishing with medical pressure sensor has actually ended up being an important aspect of developing medical applications.

Listed below, we check out below different uses of medial pressure sensor in healthy keeping innovation.

Getting the mix right in medical ventilators.

A ventilator works by blending air with pure oxygen to assist the respiratory function of a patient. Differential or gauge pressure sensors are usually sited in between regulators and valves to make sure the air and oxygen are mixed in the best amounts. In this type of application, little surface-mount sensors are perfect; they will generally be defined for a pressure range of 5in or 2in H2O and are readily available with either analog or digital (I2C) outputs.

Regardless of being low and little power, these low pressure sensors can frequently consist of an incorporated DSP (digital signal processor) for compensating for non-linearity, offsets or the effects of temperature.

Keeping Track of oxygen therapy effectiveness.

Oxygen treatment is available in a variety of types, as focused oxygen could be an efficient preliminary treatment for asthma, bronchitis and oedemas, in addition to cardiac arrest.
Oxygen treatment systems utilize differential pressure sensors at numerous points in the system to keep track of the pressure of the oxygen as it is combined with atmospheric air.

These sites are typically at the outlet of the oxygen tank, inline with the pressure regulator, and beside the circulation control valve (see diagram right).
The medical pressures sensor in this application are most likely to be differential pressure sensors with a scale of approximately 4 kPa.

Medical Pressure Sensorin an oxygen concentrator

Providing hyperbaric therapy.

Raising the atmospheric pressure in a sealed chamber consisting of a patient is called hyperbaric treatment and can possibly be reliable for a variety of conditions. It’s utilized to deal with decompression sickness experienced by divers, and can likewise assist patients with skin grafts or burn injuries. It can likewise work out in dealing with carbon monoxide gas poisoning and even some necrotizing infections.

Medical pressure sensor can keep track of pressure and record it inside the chamber and decide the pressure volume used in treatment process. This will generally take the kind of an absolute pressure sensor efficient in measuring pressures approximately around 100 kPa.
Even this most commercial of treatments is making inroads into patient’s residences, as ‘soft’ chambers turn into significantly offered – although the pressures these soft chambers can attain are lower than the professional-grade ‘difficult’ chambers.

Typically, gauge medical pressure sensor can measure pressure around 0.3bar to 0.5bar in a soft chamber, while a tough chamber would use gauge pressure sensors able to measure as much as 6 bar.

Offering positive pressure masks to treat sleep apnoea.

Sleep apnoea is a condition that triggers the patient to stop breathing while asleep. Left unattended it can result in a variety of major conditions, from chronic tiredness to possible cardiac arrest.

The treatment includes employing an equipment called a constant positive air pressure device, or CPAP, which provides air at a positive pressure to a mask used over the nose and mouth of the client. An air flow pressure sensor is employed to keep an eye on the atmospheric pressure, discovering when the patient is taking in and right away switching on a fan to produce positive pressure to open the respiratory tracts. As the patient breathes out the fan is shut off, permitting the patient to breathe out without requiring them to eliminate in opposition to the positive pressure.
Sleep apnea makers will likely utilize a differential pressure sensor able to measure pressures approximately 4 kPa.

Automating Drug Infusion

These fluids can be administered either intravenously, subcutaneously orstraight into a vein, and aregenerally provided utilizing infusion pumps. In order to make sure the right volume of fluid is administered at the proper rate, the pumps utilize a number of sensors consisting of gauge and differential pressure sensors, to carefully manage the circulation and keep track of liquid.

When it comes to drug delivery process, differential pressure sensors are chosen to measure the liquid pressure that transfuse into client. (see diagram listed below)

This makes sure the ideal volume of drugs is provided at the correct time throughout the day and night, without the requirement for consistent medical attention. Many kinds of medical pressure sensors can be calibrated to measure pressure range of 0.5 to 10.0 micro litres/min.

Medical Pressure Sensor used to control drug delivery

Measure In-Ex vivo blood pressure.

In vivo high blood pressure sensing includes implanting a sensor into the body. It can now be attained making use of small absolute pressure sensors created for this function. From outside of sufferer’s body, medical pressure sensor can be sensing and measure high blood pressure in and between systolic and diastolic, that is so called ex vivo high blood pressure measurement.

Either in and ex vivo high pressure used sensing element need to be fabricated and calibrated to measure pressure, such as 300mm Hg maximal, nevertheless in vivo applications tend to choose absolute pressure sensors, while ex vivo favour gauge pressure sensors.

Another kind of gauge pressure sensors which fabricated based on MEMS technology, can measure the intraocular pressure of a sufferer’s eyes, that is particularly essential after an operation to replace the cataract.

Medical Pressure Sensor-1-Eastsensor

Manufacturers are now producing an ever-widening series of pressure sensors for medical applications, consisting of disposable pressure sensors based upon MEMS techniques that can be applied inside the body or in-line with fluids going into the body. These are produced in tidy spaces and according to industry-accepted standards consisting of those created by the Association for the Advancement of Medical Instrumentation (AAMI).

Medical pressure sensor has been account for critical and essential parts of healthcare supplying chain, on the other hand, precise measurement of pressure level in gas and liquid within the sufferer’s body has ever-increasingly been requested by more and more people.

Future advancements will make it possible for more advanced, and ever smaller sized medical pressure sensor and other medical devices as being established, along with reducing the rate point for home-use equipments. One substantial outcome will be a raised lifestyle for an aging population.

Automobile Pressure Sensor Applications in 2021

Automobile Pressure Sensor Applications in 2021

Driving would be a completely different experience without all the pressure sensors utilized throughout the modern-day car, assisting to handle whatever from braking to electrical windows, exhaust emissions to power steering.

Many of the important systems in a car rely on pressure sensors to measure and keep track of crucial specifications, which has ended up being main aspect in making our roadways more secure, reducing pollution, and enhancing our driving experience.
How precisely do pressure sensors make it possible for much better automobiles, and what do manufacturers require to understand in order to do that?

Application 1: Discovering early faults in hydraulic brakes

That simple braking experience you’re utilized to and the responsiveness of the pedal below your foot is down to a complicated mix of elements, consisting of automobile pressure sensors.

In-car systems detect the pressure you’re using on the pedal then enhance it to make your efforts more reliable. These systems utilize an absolute pressure sensor to keep an eye on the vacuum preserved in 2 different chambers inside the brake servo (see diagram listed below).

Automobile pressure sensor-4-Eastsensor

Under typical operating conditions, when the brake pedal is depressed, it enables air pressure to stream into among the chambers. This increases the pressure on a diaphragm, which, consequently, increases the effort used on the master cylinder. When the brake pedal is launched the vacuum is brought back utilizing a vacuum source, which might be by means of a devoted pump or drawn from the manifold.
If the vacuum in one or both chambers cannot be kept or brought back, a fault condition emerges.

An absolute pressure sensor is utilized to keep an eye on the pressure in the chambers and notify the driver or engine management system if the pressure inside the chambers is not low enough to get efficient.
Without a method of measuring the pressure inside the chambers, the system might stop working without having the driver understanding and lead to an abrupt loss of braking effectiveness, simply when it’s required most.

Manufacturers are utilizing Manifold Absolute Pressure (MAP) sensors in this type of application, which may possibly be provided in surface-mount plans and have the ability to measure pressures in the variety of 10 to 150 kPa (kilopascal) with a precision of 1% throughout the whole range.

Application 2: Optimizing the fuel mix to match the air pressure.

Making internal combustion engines as effective as possible has much to do with getting the fuel mix ideal for the fundamental conditions. This consists of the real and wanted speed, obviously, however likewise consists of making changes for the current engine speed, and the engine and manifold temperature level.

When changing the fuel mix and ignition timing, it isn’t simply the air temperature that requires to be measured though; the air pressure is likewise a crucial aspect. Here, absolute pressure sensors are utilized to offer the engine management system (EMS) with the info it requires.

The sensors are utilized to measure the pressure inside the manifold and, since air is attracted from the surrounding location, the outdoors atmospheric pressure too. Barometric atmospheric pressure can have a substantial impact on fuel mix, so by measuring it and compensating for modifications, the EMS can tune the engine for optimal effectiveness, whether the cars and truck is at water level or 20,000 feet above it.

MAP sensors are utilized here, too, however in this particular case they require to become able to measure pressures as high as 400 kPA.

Application 3: Cleaning exhaust filters automatically

Diesel fuel is among the most typical types of fuel for lorries, specifically big haulage, building and construction and farming lorries, and pressure sensors are important in making diesel motors as well-maintained as possible.

Particle filters inside the engine are utilized to record the soot and other particles present in the exhaust gas prior to it can leave into the environment. The filters then require cleansing, which is done by burning the particulates.

This can either be attained utilizing an active system which heats up the filter to a temperature where the soot combusts, or a passive system utilizing a catalyst.
In the active system (see diagram listed below), pressure sensors are utilized to measure the exhaust gas pressure. When pressure throughout the diesel particle filter (DPF) reaches a limit, the cleansing procedure is activated. This could be measured by utilizing 2 absolute pressure sensors or a differential pressure sensor.

Automobile pressure sensor is used to measure the exhaust gas pressure

Application 4: Guaranteeing the catalytic converter is sealed

In a passive system, particulates in exhaust gases are ruined utilizing a catalytic converter. In this particular case a pressure sensor is utilized to make certain the system can work effectively even at low engine temperature levels.
The catalytic converter requires to get up to temperature level rapidly so as to work effectively. Generally, it requires to reach in excess of 300 ° C however when the engine is cold so too is the catalytic converter. Feeding air into the exhaust manifold activates an exothermic procedure, which assists raise the temperature of the catalytic converter.
When at temperature level, the pump for the secondary air valve is turned off and the system is sealed with a valve. Utilizing an absolute pressure sensor placed in between the valve and the pump offers the needed guarantee that the valve is closed correctly and the rest of the system is secured from damaging exhaust gases.

Application 5: Keeping track of exhaust recirculation

Automobile pressure sensor are under pressure to lower total engine emissions, and one tool in package is to recirculate portion of the exhaust gas.
Efficient in both fuel and diesel motor, the strategy decreases the temperature level in the combustion chamber, which has the impact of decreasing the quantity of Nitrogen Oxide produced and released.

Controlling the engine gas recirculation (EGR) process includes utilizing an absolute pressure sensor to keep track of the pressure at the valve. Without having that control the system might end up being unsteady and lead to too little or too much gas recirculation.
The producers of automobile pressure sensor are continuously aiming to enhance their procedures to provide pressure sensors that are much better able to stand up to the extreme environments present in this particular class of application.

Automobile pressure sensor-2-Eastsensor
Automobile pressure sensor-3-Eastsensor

Application 6: Examining the pressure of critical fluids

Possibly the absolute most typical usage for an electronic pressure sensor is to measure the pressure of the lorry’s crucial fluids for example, engine transmission, oil and transmission oil, and the hydraulic oil in the braking system, cooling system and fuel systems.
An electronic automobile pressure sensor will have a part of its structure exposed to the fluid being measured, so they require to become durable and robust. Normally, it will utilize the piezoresistive effect, which discovers the modification in resistance of a material arising from deflection brought on by the pressure put in by the fluid.

Automobile pressure sensors targeting this application area will generally have the ability to stand up to severe environments, and be sealed to IP 6k 9k (dust tight, high-pressure steam/jet cleansing), and have the ability to measure pressures from 0 bar to as much as 600 bar throughout an operating temperature level range of -40 to +125 ° C.

Application 7: Stopping doors from catching your fingers

Electric door closing on vehicles is an excellent invention however if you (or somebody smaller sized) gets in between the door and the frame at the incorrect time, problem can result– however automobile pressure sensors exist to assist.

Utilizing relative pressure sensors linked to a sealed hose pipe and installed around the edge of the doorframe, any blockage could be identified rapidly and dependably.
Any compression of the tube triggers the pressure inside to increase, which is immediately gotten by the relative pressure sensor and communicated to the automobile’s security system. It will stop closing; the very same method works for windows too if the door is electrically triggered.
Sensors created for this emerging application are normally compliant with the PSI5 (Peripheral Sensor Interface 5) protocol, which was initially established as a reputable user interface in between air bag sensors and ECUs, and utilizes a twisted-pair that brings both power and information. Pressure sensors created for this safety-critical application run over a series of around 50 to 110 kPa.

Application 8: Finding leaking vapours

A part of the obligation of automobile pressure sensor is to keep the environment devoid of possibly hazardous vapours produced by combustion engines.
New petrol automobiles now consist of a system that avoids these vapours from getting away the sealed fuel system, typically by routing the vapours to an evaporative system, which includes triggered carbon. Air is combined with the vapours so they can be securely burned up by the engine. Called evaporative emission control (EVAP) systems, they are strictly evaluated.

An absolute pressure sensor keeps an eye on the stability of the sealed system at all times, signaling the automobile (and motorist) if a leakage happens. Without having the automobile pressure sensor keeping an eye on the system, vapours might leave in case of a breach, not just launching damaging vapours into the environment however likewise putting the manufacturer in danger of prosecution for not abiding by local guidelines.
The barometric sensor will likely be located inside the fuel tank, and might supply either an analog or digital output, measuring a pressure range of around 40 to

115 kPa with a precision of 1.5 kPa or much better.

Application 9:Triggering airbags faster

Cars and truck makers are continuously innovating to enhance traveler security. Modern cars and trucks do not simply have the air bags in the control panel; they have them throughout the interior, consisting of air bags in the door to secure residents in case of a side effect.
The abrupt pressure change that happens in the door cavity throughout a side effect can be found utilizing a relative pressure sensor, frequently much faster than utilizing other methods. Utilizing the ideal kind of sensor in this application informs the cars and truck’s security system to release the air bag within a couple of hundredths of a generally much and 2nd quicker than a front air bag system runs.

Application 10: Launching pedestrian airbags

In the regrettable occasion that an automobile strikes a pedestrian, a current innovation utilizes pressure sensors to release a security mechanism (an active bonnet system) which is created to minimize the effect to the pedestrian if they arrive at the bonnet.

By putting relative pressure sensors in the front bumper of a cars and truck, any deformation to the bumper may possibly be found instantly. If this takes place, the cars and truck’s security system can trigger a compressed air reserve in the engine bay, which presses the bonnet up and towards the front of the cars and truck.

The raised bonnet (as revealed listed below) produces a barrier in between the pedestrian and the more difficult elements of the engine, hence minimizing the prospective seriousness of the effect.

Automobile pressure sensor elevated bonnet

Some automobiles likewise set up an air bag from the engine bay that covers the windshield to additional secure the pedestrian.

Automobile pressure sensors play an important function in each of these creativities, producing a cleaner, smoother, and more secure ride.
The automobile market is now among the biggest markets for pressure sensors and is most likely to stay so because of the big range of methods they’re utilized.

From a host of security features to minimizing air pollution and optimizing engine effectiveness, automobile pressure sensors are main to the modern-day car experience. Without them, we might quickly still be beginning our vehicles with a crank, changing equipments with 3 sticks and hoping we do not require to stop too rapidly!

Recommended Model of automobile pressure sensor: EST3130

5 Pressure Sensor Working Principles You Need to Know

5 Pressure Sensor Working Principles You Need to Know

With an expanding pressure sensor market as well as an increase in applications for the technology, you are bound to deal with kinds of different pressure sensors.
Whether you are fresh to the advancement or have dealt with pressure sensors for numerous years, how certain are you with a few of the modern technologies as well as principle associated with pressure sensor choice?
Today, I will ideally cover the majority of the terms and also questions you might have about pressure sensor. And also, I will certainly provide the easy contrast in between the similar terms, get the verdict of pros and also cos for every principle, so you will throughout our goal to choose the very best suitable pressure sensor for your application.

Pressure sensor working principle
An pressure sensor trusts a physical action to applied pressure, and then gauging the resulting proportional modification in an electronic format. Such digital format commonly includes adjustments in capacitance, or changes in ohmic resistance of a strain gauge or piezoelectric element, which are all proportional to the size of the deflection when pressure is used.

1, Strain Gauge Pressure Sensor

In a strain gauge type pressure silicon, sensing unit or foil strain gauges are organized as a Wheatstone bridge. The resulting signal is after that boosted as well as conditioned to provide an appropriate transducer-voltage or transmitter-current output agent of the employed pressure.

There are many types of strain gauge, usually can be summarized as below varieties:

  • Fine wire strain gauge (also called Metallic wire-type strain gauge)
  • Metal foil strain gauge
  • Thin-film strain gauge (also called metal thin film strain gauge)
  • Semi-conductor strain gauge (also called solid state)
  • Diffused silicon semi-conductor strain gauge (also called Diffused Silicon Piezo-resistance)
  • Thin-film semi-conductor strain gauge

Pressure Sensor Strain Gauge - Eastsensor

No matter it is mechanical strain gauge or capacitance and inductance-based stain gauge, they are working properly via Wheatstone Bridge which constructed on substrate using below techniques:

  • Bonding
  • Pasting
  • Coating
  • Printing
  • Sputtering (Vacuum deposited)
  • Photolithography each etching
  • Chemical sediment

Advantage of Strain Gauge Pressure Sensor

  • Can be employed to measure both static and dynamic strain
  • Medium or small size with light weight
  • Relative low cost, variety, easy to choose and use

Disadvantage of Strain Gauge Pressure Sensor

  • Can not measure low pressure than 1000pa
  • Accuracy is not as high as required (normally 1%)
  • Temperature drift always needs compensation

2, Capacitive Pressure Sensor

Pressure Sensor -Metal Capacitive-Eastsensor

Metal Capacitive Sensing

Pressure Sensor-Ceramic Capacitive -Eastsensor

Ceramic Capacitive Sensing

A capacitive pressure sensor includes a capacitor with one inflexible plate as well as one adaptable membrane layer as electrodes. The area of these electrodes being dealt with, the capacitance is proportional to the distance in between the electrodes. The pressure to be measured is applied to the flexible-membrane side, and the resulting deflection creates an adjustment in capacitance that can be measured making use of an electric circuit.

Two types of capacitive pressure sensors are typically accepted and also released worldwide, they are metal capacitive pressure sensing as well as ceramic capacitive sensing.

2.1, Metal Capacitive Sensing

Metal capacitance pressure sensor measures the change in capacitance in between a metal diaphragm as well as a repaired metal plate. The capacitance in between two metal layers adjustments if the range in between these two plates changes as a result of used pressure.
The diagram listed below highlights the operating principle behind metal capacitive pressure sensing.

Pressure Sensor Capacitive Eastsensor

The capacitive pressure transducer relies on capacitance change produced by deflection of the membrane which alters the capacitor geometry.

Advantage of Metal Capacitive Pressure Sensor

  • Proof & burst pressure is better than others
  • High accuracy can be expected as 0.075%-0.1%/FS
  • Minimal measurable range can be 100pa
  • Low power consumption

Disadvantage of Metal Capacitive Pressure Sensor

  • Max measurable range usually no more than 400bar
  • Bigger size with heavier weight usually
  • Relative higher production cost

Recommended Models of Metal Capacitive: ESS343

2.2, Ceramic Capacitive Sensing

Ceramic capacitor technology makes use of a set ceramic base and a movable ceramic diaphragm structure. The movable diaphragm is sealed as well as repaired with the base with a technique such as glass slurry.
An electrode pattern is printed on the within between both to create a variable capacitor. When the medium pressure on the diaphragm changes, the capacitance in between both changes accordingly. The signal is transformed as well as conditioned by a conditioning chip and then output to a succeeding stage for usage.

Advantage of Ceramic Capacitive Pressure Sensor

  • Wide pressure range: 6kpa-500bar
  • High over pressure: 20X-30X, good for automotive industry
  • Dry type, no oil-filled, good for Food, Medicine industry
  • Better corrosion and chemical resistance.

Disadvantage of Ceramic Capacitive Pressure Sensor

  • Non-linear output
  • High output impedance
  • Aring aging problem
  • Cannot reach high capacitance levels of polarised types

3, Piezoresistive Pressure Sensor

Pressure Sensor-Silicon piezoresistive -Eastsensor

Silicon piezoresistive Pressure Sensor

Pressure Sensor-Metal thin film piezoresistive -Eastsensor

Metal thin film piezoresistive pressure sensor

Pressure Sensor-Ceramic piezoresistive -(Thick Film type)

Ceramic piezoresistive pressure sensor

The piezoresistive measuring principle manipulates the change in the sensing unit elements electric properties when it warps, the force put in on the sensing unit element as pressure is used triggers it to deform as well as in doing so alters its electrical properties, the electric signals which change along with the pressure a transmitted outward with ultra-thin bonding wires, this permits the modification in the electric signals to be Measured

In piezoresistive pressure sensors, there are 4 resistors released on diaphragm in order to measure the outcome of physical pressure applied upon them.
Any kind of perceptible modification in resistance is being converted, with a Wheatstone bridge circuit right into an output voltage.

The piezoresistive pressure measurement principle is among the firstly developed in MEMS technology and it was created many years prior to the capacitive one. Because of this, it is most frequently utilized. Due to their widespread as well as reduced production cost, piezoresistive pressure sensors are widely used in customer electronics and the vehicle industry, in addition to in home appliances.

Pressure Sensor Piezoresistive - Eastsensor

In existing globe, vary from the diaphragm and substrate material, piezoresistive pressure sensor can be acknowledged as three preferred types:

  • Silicon piezoresistive types
  • Metal thin-film piezoresistive (thin film) kinds
  • Ceramic piezoresistive (Thick film dry type)types

3.1, Silicon piezoresistive Pressure Sensor

Silicon piezoresistive technology is understood by the piezoresistive attributes of semiconductors. The piezoresistive properties of semiconductor materials depend upon elements such as the kind of material, the doping focus, and also the crystal orientation of the crystal.

Silicon piezo-resistive pressure sensor utilizing the sensing unit elements which basically includes doped silicon (P type), it is really similar to the contemporary integrated circuit that are used in laptop computers or tablets today. Simply put, by including thoroughly controlled amounts of pollutants (dopants) to the semiconductor (N type substrate), extra lightly doped silicon results in a greater resistivity and also a higher gauge factor. This likewise boosts the thermal sensitivity of both the resistance and also gauge factor.

Similar to a strain gauge, a piezoresistive sensing unit includes a diaphragm onto which four pairs of silicon resistors are bound. Unlike the construction of a strain gauge sensor, here the diaphragm itself is made from silicon and the resistors are diffused right into the silicon throughout the production procedure. The diaphragm is completed by bonding the diaphragm to an unrefined wafer of silicon.

To boost the dielectric resistance of silicon piezoresistive technology, some unique product packaging procedures are utilized, oil filling is one of the most popular one.

Instead of pressure on the diaphragm to extend the cables and also change the resistance straight, people can also make use of type of medium to move the pressure and strength on the diaphragm, one of the most used mediums is silicon oil, as necessary, the pressure sensor or transmitter created with this technique are typically called Diffused Silicon Oil-Filled products.

Pressure sensors that utilize silicon piezo-resistive sensing elements offer several benefits over other pressure sensing innovations, they are tiny, lightweight, highly repeatable, secure with time, dynamically receptive and also really conscious variants in pressure.

Advantage of silicon piezoresistive pressure sensor

  • Tiny dimension
    It can be personalized to 45mm overall length including electric and also procedure ports, portable size will certainly conserve area and minimize weight for some special applications.
  • Long terms security
    Silicon piezoresistive is not glued, printed or electro-plated to the surfacearea to the sensing diaphragm, so it has no bonds and therefore are very stable in comparison, 0.1% is generally assured, 0.2% is optimum for a lot of range span,
  • Stable and durable under most conditions
    The combination of a high flexibility material and near flawlessly adhered and integrated generates a structure with really little hysteresis making certain that pressure analyses are specific regardless of the instructions of changing pressure.
  • High signal output sensitivity
    The relative high degrees of voltage decline can be attained throughout semiconductor strain gauges for aprovided pressure change which allows individuals to make better use of analogue to digital resolution and improve signal to noise
  • Great for both dynamic as well as static pressure measuring
    Unlike piezoelectric pressure sensor that just utilized to measure dynamic pressure changing, piezoresistive andalso measure both static pressure and also dynamic pressure.
  • Can be commonly used in lots of industries
    Pressure sensor that use silicon piezoresistive sensing elements supply several advantages over various other pressure sensing innovations, it can be deposited inthe majority of the modern-day sectors.
  • An upgraded version of semiconductor straingauge
    Solid-state diffusion makes 4 silicon resistors doping on N type substrate, creating electrical signal by resistance changing on Wheatstone bridge, no glue, bond, 100% flexible, reduced hysteresis

Disadvantage of silicon piezoresistive pressure sensor

  • Temperature performance
    Temperature drift which generally because of difference resistance property of 4 doped silicon resistors
  • Power excitation
    Relative high excitation power called for, so silicon piezoresistive is notappropriate for battery powered option
  • Shock resistance
    Even if the substrate material is n-type mono-crystalline silicon layer, that can make silicon sensing element more elastic, nonetheless in some heavy shock application such as hydraulic pressure system or water hammercircumstance, the repaid altering shock pressure can possibly over the pressure rate of silicon piezoresistive sensor diaphragm, in case of that, to prevent and also decrease the overpressure damage, thin film piezoresistive technology is
  • Chemical corrosion
    SS316 is the most common metal utilized in silicon capsule construction, nonetheless some chemicals are very corrosive to SS316, to solve this problem, people canmake use of other material such as hastelloy, monel, inconel and titanium for rather, nevertheless such unique material constantly cost greater than stainless-steel, shall we have cost competitive method to solve chemical concern? Certain, ceramic piezoresistive sensing can do the task well.
    Some of the above prospective problems that should be talked about with manufacturers before choosing silicon pressure sensors.

Recommended Designs of Silicon Piezoresistive

3.2, Metal thin film piezoresistive pressure sensor

The sensing unit elements can be bonded on to the surface area with glue like regular strain gauge type, or with the conductor like semiconductor strain gauge type, or with doping the P silicone on N stye substrate like diffused silicone type.

The sensing elements can additionally be deposited on the diaphragm by vaporized or sputtered, using that, it can eliminate possible troubles with adhesives failing at high temperatures as well as makes it easier to create little tools.

Among the means by spluttering the sensing element on metal thin film substrate, called metal thin film (MTF) piezoresistive pressure sensor

The term “film” consists of reasonably thin metal films, having a density of regarding 100 nm to about 10 microns, thin metal films, having a density of concerning 10 nm to about 100 nm, as well as ultra thin metal films, such as discontinuous or island type metal films having a thickness of less than about 10 nm. The term “metal” includes pure or essentially pure steels as well as metal alloys.

Advantage of Metal Thin Film pressure sensor

  • Reduced gauge factor
    Contrast to thick film (ceramic piezo-resistive), thin metal films havean instead low gauge factor (2 ˜4). Due to the fact that they have much smaller sized resistance and can bear a lot higher existing density than semiconductor piezoresistors, they can generate comparable signal strength to semiconductor
  • Much less noise and highly sensitive
    The lower resistance produces much less thermal noise. Given that metal films have several orders of magnitudegreater service provider density than semiconductor piezoresistors, their 1/f noise will be significantly With gadgets working at resonant frequency as well as doing ac measurements, thin metal films can be highly sensitive.
  • Construction flexibility
    In contrast to semiconducting piezoresistors, metal thin film piezoresistors can beproduced at dramatically reduced cost. Metal films of thickness from 10 nm to 10 microns can be merely evaporated or sputtered onto practically any type of substrate, such as Si, SiC, SiN, SiO2, glass and also plastic materials.
  • Anti-shock and vibration
    The metal thin-film sensor is extremely stable as a result of the materialsIn addition, it is resistant to shock and vibration loading in addition to dynamic pressure elements. Since the materials utilized are weldable, the sensing unit can be bonded to the pressure connection − hermetically sealed and with no extra sealing materials.
  • Ideal option for heavy duty equipment
    Because of several excellent attributes of metal thin film, such as lower gauge factor,extremely well burst pressure security capability (thanks to the impressive ductility of metal thin film), boosted output signal, well performance at heat, moderate manufacturing cost, it can be among the best choices when getting pressure sensor for heavy duty industries.
  • Better for clinical sector
    As a result of the very secure capability (less than 0.1%/ FS) and also high precision, and good metal hygiene problem, thin-film piezoresistive sensing unit likewise made use of in medical facility for numerous clinical case such as infusion pump, insulinpump,

Disadvantage of Metal Thin Film pressure sensor

Metal thin film has so many benefits over, nonetheless no person is best, listed below points need to be considering

  • Not ideal to measure absolute pressure
  • Not suitable remedy for reduced microwave frequencies jobs
  • Cost higher than thick film pressuresensor
  • Complicated fabricate procedure

 

Recommended Models of Metal Thin Film Piezoresistive

3.3, Ceramic piezoresistive pressure sensor(Thick Film type)

Ceramic piezo-resistive pressure sensor is a dry-type thick film pressure sensor which made of ceramic Al2O3 96% by piezo-resistive technology, work following the piezoresistive principle, the Wheatstone bridge is screen printed straight on one side of the ceramic diaphragm and also the diaphragms opposite side.

The ceramic piezoresistive pressure sensor capsules are made with a ceramic base plate and also a flush diaphragm and also work following the piezoresistive principle. The Wheatstone bridge is screen printed on one side of the flush ceramic diaphragm which is, consequently, glued to the sensing unit’s body. The bridge encounters the within where a dental caries is made as well as the diaphragm’s contrary side can for that reason be exposed directly to the medium to be measured.

Pressure Sensor-Ceramic piezoresistive -ESS501-Eastsensor

To conclude, ceramic piezoresistive technology makes use of a thick film printing process to print a Wheatstone bridge externally of a ceramic structure, and also uses the varistor effect to convert the pressure signal of the medium right into a voltage or current signal.

Advantage of ceramic piezoresistive pressure sensor.

Ceramic piezoresistive technology has the advantages of moderate cost and also basic procedure over traditional stainless-steel solutions, based on our experience, we’ve finish up the main features of ceramic piezoresistive go as listed below.

  • A lot more solid and steady.
    Since ceramic piezoresistive do not count on oil, the diaphragm can be thicker,as well as the pills can be made much shorter than silicon, ceramic piezoresistive sensors does not bring the threat of a leak that might endanger an entire set of sensors.
  • High stability.
    Due to the fact that they are tougher, ceramic pressure sensors will certainly not differ their calibrated establishing even after multiple operating cycles,hence minimizing the danger of sensing unit drift. All these attributes make ceramic pressure sensors ideal for a lot of industrial applications, particularly if precision, vibrant range, and also corrosion resistance are critical requirements.
  • Chemically inert.
    Ceramic is naturally high corrosion defense from acidic or alkaline remedies, the disc designed pressure sensor elements are made from 96% pure alumina ceramic which unlikelots of metal based sensing units, is chemically inert as well as consequently untouched by many corrosive compounds.
  • Light weight & low profile.
    As stated over, ceramic pressure sensing capsules can be much smallersized than others, so their weight is light accordingly, they can be easily packaged to fulfill your very own housing need, what’s more, ceramic thermal security can make its operating temperature from -40 to 105 ° C, so they can withstand high operating temperatures as well as pressures without losing level of sensitivity at reduced pressure values. They tolerate fairly high over pressures too.

Disadvantage of ceramic piezoresistive pressure sensor.

  • Modest overload performance.
    As a result of the less flexible nature of ceramic itself, thestandard hollow structure only bears the pressure of the diaphragm, which has bad resistance to overload. when the pressure of the medium to be measured is strained, the ceramic resistance sensing unit will certainly take the chance of the diaphragm rupture and the medium leak.
  • Output sensitivity.
    The signal output sensitivity of this technology isreduced, the range a minimum of start from 50kpa for pressure sensor, as well as 100kpa for pressure transducer is a must, as well as the upper limit range for ceramic piezoresistive disappears than 50bar for sensor, 600bar for pressure transducer, so if pressure range exceed that, ceramic piezoresistive will certainly be not the most effective solution;.
  • Temperature drift.
    Typically, if adopts ceramic piezoresistive solution atheat, it will trigger noticeable temperature drift if over 120 ° C.
  • O-Ring aging issue.
    Unlike silicon piezoresistive which the stainless steel can be welde, for ceramic piezoresistive pressure sensor,produced with suitable O-Ring material is very important to improve sealing performance nonetheless, regardless of commonly NBR or Viton will certainly run the risk of the leakage issue at long run, particularly under rough problems.

Recommended Models of Ceramic Piezoresistive

4, Piezoelectric Pressure Sensor

Piezoelectricity is the charge produced throughout certain materials when a mechanical stress is used.

Piezoelectric pressure sensors make use of an element made from a material which creates electric power when they are under strain, such as quartz or tourmaline.
When a force is applied to a piezoelectric material, an electrical charge is generated across the faces of the crystal. This can be measured as a voltage proportional to the pressure.
Most notably, they just produce power when the pressure adjustments (The output signal will progressively drop to zero, also in the visibility of consistent pressure), and also are because of that appropriate just for dynamic pressure measurements (piezoelectric sensors are not normally ideal for determining fixed pressure).

Pressure Sensor Piezoelectric - Eastsensor
Unlike piezoresistive as well as capacitive transducers, piezoelectric sensor elements call for no external voltage or existing resource. They create an output signal directly from the applied strain.
The output from the piezoelectric element is a fee proportional to pressure. Discovering this needs a cost amplifier to transform the signal to a voltage.

Advantage of piezoelectric pressure sensor

  • Ruggedness
    The effectiveness, high frequency as well as rapid response time of piezoelectric pressure sensors mean they can be made use of in a vast array of industrial and also aerospace applications where they’ll be subjected to range of rough environments (high temperatures as well as pressures).
  • High temperature
    Aside from the connected electronics, piezoelectric sensing units can be utilized at high temperatures. Some materials will certainly operate at approximately 1,000 ºC. The sensitivity may change with temperature however this can be lessened by appropriate selection of materials.
  • Reduced power consumption
    The output signal is produced by the piezoelectric element itself, so they are naturally low-power devices.

Disadvantage of piezoelectric pressure sensor

  • At risk to shock and also vibration.
  • Can only measure pressure in dynamic
  • Make intricacy (need to be very carefully created and also positioned as close as feasible to the sensor to decrease noise and other signal mistakes).

 

5, MEMS Pressure Sensor

It’s quite simple to think of a piezoresistive or capacitive pressure sensor as a huge device like a through-hole electronic element or a component all set to screw into the side of a storage tank– nonetheless that’s not constantly the situation.
A piezo or capacitive pressure-sensing system can additionally be produced on silicon as a MEMS (Micro Electro Mechanical System) device and also packaged as a portable surface-mount system generally gauging only about 2-3mm per side.

MEMS tools are generated in silicon utilizing doping and etching procedures. These procedures are carried out at chip range, resulting in a tiny gizmo that can be co-packaged with signal-conditioning electronics. The electronic wiring may make up easy boosting to produce an analogue output, and also might likewise consist of analogue-to-digital conversion to generate an electronic output.

Advantage of MEMS pressure sensor

  • High linearity as well as security.
  • Tiny dimension lightweight.
  • Low power make-up.

Glass micro-fusion Pressure Sensor

Glass micro-fusing technology uses a high-temperature sintering process that incorporates a silicon strain gauge with a stainless-steel structure, it is usually appropriate for high pressure range (100Mpa and over).

Sapphire Pressure sensor

Sapphire Pressure sensor is sort of SOS (silicon-on-sapphire) pressure measurement type, that is normally considered as one of the services to handle ultra-high temperatures, chemical inert and abrasion immune instances.

Fieldbus, ProfiBus and HART Protocols

At present, there are three major digital protocols that are used in process automation. These are HART, ProfiBus PA and Foundation Fieldbus H1. Let’s take a look at how they work:

Foundation Fieldbus Protocol

The Foundation Fieldbus is a digital, serial, two-way communications system used for base-level automation in a plant or a factory. It is different from other networking technologies that are used for the same purpose. This is because it is not only a protocol used in networking; it is also a programming language that can be used to build control strategies. The Foundation Fieldbus does not merely tell you what to do; it also tells you how to do it. Instead of being limited to a central controller, the Foundation Fieldbus system distributes control to field devices.

Foundation Fieldbus, HART, ProfiBus
For example, the positioned Fieldbus valve usually acts as a controller for the loop it is a part of. Both the Foundation Fieldbus system and the traditional DCS systems make use of a PID controller. However, in the Foundation Fieldbus, the role of the PID controller is more sophisticated as its control can be limited to just one designated feedback loop and not any other loops. This new architecture is called the Field Control System and is an alternative to DCS. It allows for decentralized control, which is a key feature of the Foundation Fieldbus protocol.

Meant to replace the previous 4-20 mA standard, the Foundation Fieldbus now exists alongside other communication technologies such as Modbus, Industrial Ethernet, and ProfiBus. It consists of the following components:

  • H1 Card: This is the interface card of the Fieldbus.
  • PS: This manages the bulk power to the Fieldbus Power Supply
  • FPS: Fieldbus Power Supply(FPS) and Signal Conditioner are integrated forms of power supply and conditioners.
  • T: This is the Terminator Component. There are two terminators for each Fieldbus segment. One is present at the Fieldbus Power Supply and the other is present at the furthest point of the segment, near the device coupler.
  • LD: The Linking Device is used with the HSE networks. Its purpose is to terminate the 4-8 H1 segments that act as a gateway to the HSE backbone network.

Other components include transducers, transmitters, etc.

HART Protocol

The HART or Highway Addressable Remote Transducer Protocol allows multiple devices to be dropped simultaneously using a single pair of wires. However, this multi-tasking capacity has not been fully utilized due to low update speeds, which are currently half a second for each device.

In most cases, HART devices are installed in a manner such that you will find them connected end to end or point to point with one pair of wires dedicated to each device. There is also a handheld communicator that is connected for maintenance and configuration.

Find out: HART Protocol EST4300 Smart Pressure Transmitter in our Shop 

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Do you really know your pressure sensor accuracy?

Do you really know your pressure sensor accuracy?

Accuracy has a price. The cost of a pressure sensor is a function of its accuracy, the more accurate the sensor the more expensive it will be. From a manufacturing point of view, the wrong sensors can cause expensive quality or efficiency problems. That is why it is important to understand how manufactures calculate accuracy and recognize what parameters to look at when comparing pressure sensors. By understanding how manufactures calculate accuracy, you will be able to make a more informed decision when evaluating pressure sensors. Ensuring the next sensor you select will have the required accuracy at right price for application.

What is accuracy? The International Electrotechnical Commission’s (IEC) definition of accuracy is the maximum positive and negative deviation from the specified characteristic curve observed in testing a device under specified conditions and by a specified procedure. Unfortunately when it comes to defining accuracy for a pressure sensor it’s more complicated. Accuracy has a large effect on the cost of a pressure sensor or even more important, the quality or efficiency of the process it is measuring. It is important to understand what factors determine accuracy and what questions to ask when selecting a sensor.

Accuracy must include Hysteresis, Non-Repeatability and Non-Linearity. Non-Repeatability and Hysteresis are well defined. Hysteresis is the maximum difference in sensor output at a pressure when that pressure is first approached with pressure increasing and then approached with pressure decreasing during a full span pressure cycle. Non-Repeatability is the maximum difference in output when the same pressure is applied, consecutively, under the same conditions and approaching from the same direction.

The term “Accuracy” exists only in the users’ language. It is not defined in any standard. Nevertheless, it can be found in many data sheets for sensors. Unfortunately, there is no common idea of what accuracy means. There is not ”one accuracy“ but a large number of different specifications with regard to accuracy, all of them together describe the “accuracy” of a device.

No linearity pressure sensor accuracy

Stability

The accuracy given in data sheets usually describes the condition of a device at the end of the production process. The device can already be exposed to environmental conditions affecting its accuracy negatively from the moment of leaving the manufacturer’s company or warehouse or during transport. It is not important how accurate the device is or if it is of a very high quality, every device changes its accuracy during its service life. This change is called long-term drift or long-term stability. The dimension of this drift is largely influenced by the operating conditions, i.e. pressures, temperatures and other influences to which the device is exposed. In many cases, stability has a larger influence on the overall deviation than e.g. non-linearity. Values twice or three times as high are not unusual. Stability data stated by the manufacturer can hardly be compared. Different standards describe very different tests for determining stability. Furthermore, none of these tests is an actual copy of the real conditions of use. This is not possible because the conditions vary too much from application to application. Consequently, stability data are only valid for uses in laboratories or under reference conditions. However, even if used under reference conditions, it is almost impossible to obtain comparable data. You cannot make time go faster. And all attempts to simulate a time lapse effect by means of thermal shocks and other methods are just attempts.

In Practice

Hysteresis and non-repeatability are pretty much the only errors you have to deal with. All other errors can be minimized or even eliminated with some kind of effort. This works easiest and clearest using the offset error. The user can read the offset error hassle-free in unpressurised condition and enter it as offset in the corresponding evaluation instrument. In order to eliminate the span error, the pressure must be regulated exactly at full scale value. This is often not possible as there is no reference value for the pressure. In order to make the pressure sensor not to measure worse than before, the reference pressure should be three times more accurate than the intended accuracy.

Most manufacturers recommend calibrating the pressure sensors once a year, to control whether they still meet their specifications. The device is not readjusted but the actual change, i.e. the drift, is analyzed. If the drift is higher than the value specified by the manufacturer, this might be an indication for a defective device. The higher the instability, the more probability that the sensor is defective. In this case, process reliability can no longer be guaranteed if the device is still being used. This check does not require much effort. Often it is sufficient to check if the zero point of the unpressurised device has changed. If the device can neither be checked in the system nor dismounted for examination, you should at least set a high value on a very good stability and respect it in your accuracy specifications. Unfortunately, these are not the only possible sources of error. Vibrations, electromagnetic interferences, mounting position of the sensor, power supply and even the load of the evaluation instrument might affect the accuracy of your pressure sensor. Therefore, individual consulting by a specialist is recommended in many cases.

In a nutshell

Do you know the exact accuracy of your sensor? Is it as good as you have expected? Or is it too good? You are the only person to decide which errors are relevant for you and which are not. The manufacturers’ application consultants explain which product characteristics are important for it and how they can be implemented in your application. This ensures that you reach your targets with optimum input. We would be well area of which is the accuracy you presently have and which is the one you actually need.

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Pressure Sensor Technology Comparison

Pressure Sensor Technology Comparison

In terms of pressure sensor technology, all pressure pressure transducers operate on the principle of converting a pressure change into a mechanical displacement, or deformation. Deformation of the sensing element is then converted into an electrical signal that is processed by the measuring system. Types of pressure transducers available in the field, either individually or in combination, are mechanical, capacitance, strain gauge piezoresistive, Piezoelectric, thin- film and quartz gauge. This article discusses how each of these types of pressure transducers operates and what are their advantage and disadvantage

Pressure Sensor Technology of Bourdon tube

Mechanical methods of measuring pressure have been known for centuries. The first pressure gauges used flexible elements as sensors. As pressure changed, the flexible element moved, and this motion was used to rotate a pointer in front of a dial. In these mechanical pressure sensors, a Bourdon tube, a diaphragm, or a bellows element detected the process pressure and caused a corresponding movement.

A bourdon tube is C-shaped and has an oval cross-section with one end of the tube connected to the process pressure. The other end is sealed and connected to the pointer or transmitter mechanism. To increase their sensitivity, Bourdon tube elements can be extended into spirals or helical coils. This increases their effective angular length and, therefore, increases the movement at their tip, which in turn increases the resolution of the transducer (Figliola and Beasley, 1991).

Designs in the family of flexible pressure sensor elements also include the bellows and the diaphragms, Fig.1.1. Diaphragms are popular because they require less space and because the motion (or force) they produce is sufficient for operating electronic transducers. They also are available in a wide range of materials for corrosive service applications (Omegadyne, 1996).

After the 1920s, automatic control systems evolved in industry, and by the 1950s pressure transmitters and centralized control rooms were commonplace. Therefore, the free end of a Bourdon tube (bellows or diaphragm) no longer had to be connected to a local pointer, but served to convert a process pressure into a transmitted (electrical or pneumatic) signal.

At first, the mechanical linkage was connected to a pneumatic pressure transmitter, which usually generated a 3-15 psig output signal for transmission over distances of several hundred feet, or even farther with booster repeaters (Omega, 1996). Later, as solid-state electronics matured and transmission distances increased, pressure transmitters became electronic. The early designs generated dc voltage outputs:10-50 mV, 0-100 mV, 1-5 V (Omega, 2003), but later were standardized as 4-20 mA dc current output signals.

However Gauges with bourdon tubes are still the most common pressure measuring devices used today. They combine a high grade of measuring technology, simple operation, ruggedness and flexibility with the advantages of industrial and cost-effective production. Needing no external power supply, bourdon tube gauges are the best choice for most applications.

In Eastsensor, we have been produced some types of mechanical pressure gauge with Bourdon tube technology to serve our customers measuring processes in many application, please check our product out below.

bourdon tube pressure gauge

Pressure Sensor Technology of Strain gauge

The first unbonded-wire strain gauges were introduced in the late 1930s. In this device, the wire filament is attached to a structure under strain, and the resistance in the strained wire is measured. This design was inherently unstable and could not maintain calibration. There also were problems with degradation of the bond between the wire filament and the diaphragm, and with hysteresis caused by thermoelastic strain in the wire (Omega, 1996). The search for improved pressure and strain sensors first resulted in the introduction of bonded thin-film and finally diffused semiconductor strain gauges. These were first developed for the automotive industry, but shortly thereafter moved into the general field of pressure measurement and transmission in all industrial and scientific applications.

Strain gauge sensors originally used a metal diaphragm with strain gauges bonded to it, the signal due to deformation of the material is small, on the order of 0.1% of the base resistance. Semiconductor strain gauge are widely used, both bonded and integrated into a silicon diaphragm, because the response to applied stress is an order of magnitude larger metallic strain gauge.

strain-gauge-visualization

Semiconductor pressure sensors are sensitive, inexpensive, accurate, and repeatable (Omega, 2003). When a strain gauge, which is shown in, is used to measure the deflection of an elastic diaphragm or Bourdon tube, it becomes a component in a pressure transducer. Strain gauge-type pressure transducers are widely used. Strain-gauge transducers are used for narrow-span pressure and for differential pressure measurements. Essentially, the strain gauge is used to measure the displacement of an elastic diaphragm due to a difference in pressure across the diaphragm. These devices can detect gauge pressure if the low pressure port is left open to the atmosphere, or differential pressure if connected to two process pressures. If the low pressure side is a sealed vacuum reference, the transmitter will act as an absolute pressure transmitter (Omega, 2003).

Bonded foil strain gauge, which  has excellent stability and good overpressure protection is the very good choice to make wide and big pressure range transmitter.

strain-guage-pressure-transducer

Pressure Sensor Technology of Capacitive

Capacitive pressure sensors use a thin diaphragm, usually metal or metal-coated quartz, as one plate of a capacitor. The diaphragm is exposed to the process pressure on one side and to a reference pressure on the other. Changes in pressure cause it to deflect 29 and change the capacitance. The change may or may not be linear with pressure and is typically a few percent of the total capacitance (Considine, 1993). The capacitance can be monitored by using it to control the frequency of an oscillator or to vary the coupling of an AC signal through a network. The electronics for signal conditioning should be located close to the sensing element to prevent errors due to stray capacitance.. The schematic of a capacitive pressure sensor is shown in Fig. 1.5 (Omega, 2003).

capacitive-pressure-sensors

Pressure Sensor Technology of Piezoresistive

The piezoresistive pressure sensor elements consist of a silicon chip with an etched diaphragm and, a glass base anodically bonded to the silicon at the wafer level. The front side of the chip contains four ion-implanted resistors in a Wheatstone bridge configuration. The resistors are located on the silicon membrane and metal paths provide electrical connections. When a pressure is applied, the membrane deflects, the piezoresistors change unbalancing the bridge. Then a voltage develops proportional to the applied pressure (Sugiyama et al., 1983). Silicon piezoresitive sensors have been widely used for industrial and biomedical electronics (Ko, et al., 1979). The piezoresitive sensors have excellent electrical and mechanical stability that can be fabricated in a very small size.

piezoresistive-pressure-sensors

Characteristics comparison between Capacitive and Piezoresistive

The pressure to capacitance difference relationship for three devices with various sizes in diaphragm and electrode areas is shown below, where Dia. represents the diaphragm diameter and EAR represents the ratio of electrode area to diaphragm area. Comparing the experimental and simulation results, the deviations could be attributed to process variations in diaphragm dimensions. Extracting the sensitivity of the devices with least square fit, the errors are within 10%.

Comparing our device with a commercially available piezoresistive pressure sensor which has similar operating range, the preliminary result shows that when both sensors are not temperature compensated and for the temperature range we tested, the temperature coefficient of sensitivity of our capacitive device is 10 times better than the piezoresistive pressure sensor.

characteristics-comparison-between-capacitive-and-piezoresistive

Advantage of Capacitive Sensing

Capacitance is a measure of energy stored between two conducting plates or electrodes holding an opposite charge. Capacitance varies according to the strength of the charge, the distance between electrode plates, and the size of the plates. By keeping the charge between capacitor plates constant, you can tell how far one plate is from another by measuring the voltage between them. Increase fluid pressure deflects the diaphragm (electrode plate), either closing or increasing the distance to the other plate, which changes the charge between plates. This simple approach proves both accurate and reliable, and offers many benefits over measuring pressure with strain gauges.

Advantage:

  • Stable:  Capacitive sensor/transmitter does not rely on an intermediate element, such as a strain gauge, to produce an output. They are also simpler and more reliable than bonded strain gauge elements because they require no adhesives, which can produce self-imposed strain from differential thermal expansion.
  • Good compatibility: Media compatibility problems of integrated strain gauge transducers are avoided in capacitive transducers because the sensing diaphragm (electrode plate) can be constructed of stainless steel, ceramics, or other chemically non-reactive materials. They also accommodate a wide range of temperatures.
  • Less error & high accuracy: Capacitive elements also produce a stronger output than strain gauge elements. Some signal conditioning is still required, but requires less amplification. Less amplification means error becomes a smaller portion of the output signal. Ultimately, accuracy is improved.
  • EMI&RFI immune: EMI and RFI can generate stray fields, introducing electrical signals that controls may “confuse” with the actual transducer output. Unlike  strain gauge elements, the high level output signal produced by capacitive type sensing elements is insensitive to low or moderate EMI and RFI, maintaining the integrity of the output.
  • Reliability for millions cycles: Capacitive-sensing elements can also withstand millions of full scale pressure cycles without affecting accuracy because they do not suffer the same effects caused by the use of adhesives.

Performance of pressure sensing devices is affected by their design and technology. When compared to strain gauge sensors, capacitive sensors produce highly accurate, stable, EMI/RFI immune pressure transducers that meet performance requirements.

Disadvantage of Strain Gauge Sensing

Strain gauges are widely used to measure, electrically, how much a material shrinks or stretches in response to an applied force, torque, or stress. Strain gauge pressure-sensing elements use a diaphragm combined with a strain gauge to generate an output signal representative of the fluid pressure.

Disadvantage:

  • Accuracy degradation: Bonded strain gauge sensing elements use an adhesive to attach the strain gauge to the diaphragm. Problems arise with this design because the adhesive often has a coefficient of thermal expansion different from the diaphragm and strain gauge. So if pressure remains constant, but temperature changes dramatically, the adhesive may expand or contract more than the diaphragm. The differential expansion could impose a strain on the strain gauge that would produce a different output signal even through the pressure did not change at all. Over time, this self-induced strain can permanently degrade accuracy.
  • No rugged structure: Furthermore, millions of expansion and contraction cycles can weaken the adhesive bond. In most cases, this deteriorates accuracy, but in extreme cases–especially when aggravated by heavy vibration–the bond can fail completely, rendering the transducer useless.
  • Incompatibility with adhesives: Integrated strain gauge sensing elements are designed with the strain gauge embedded in a diaphragm made of silicone or other material. While they avoid adhesives–and the problems associated with them– integrated strain gauge sensing elements compromise the fluid compatibility common with stainless steel diaphragms.
  • Vulnerability: Diaphragms of silicone and other materials are attacked by a wide variety of chemicals found in industrial fluids. They also accommodate a narrower range of temperatures. Even if chemical incompatibility does not cause transducer failure, it can change the physical properties of the diaphragm, which degrades accuracy.
  • EMI&RFI problem: Both types of strain gauges sensing elements produce relatively weak output signals. This means that weak or moderate EMI and RFI can degrade output.

Advantage of Piezoresistive pressure sensors

Piezoresistive based transducers rely on the piezoresistive effect which occurs when the electrical resistance of a material changes in response to applied mechanical strain. In metals, this effect is realized when the change in geometry with applied mechanical strain results in a small increase or decrease in the resistance of the metal. The piezoresistive effect in silicon is due primarily to changes at the atomic level and is approximately two orders of magnitude larger than in metals1. As stress is applied, the average effective mass of the carriers in the silicon either increases or decreases (depending on the direction of the stress, the crystallographic orientation, and the direction of current flow). This change alters the silicon’s carrier mobility and hence its resistivity. When piezoresistors are placed in a Wheatstone bridge configuration and attached to a pressure-sensitive diaphragm, a change in resistance is converted to a voltage output which is proportional to the applied pressure.

The piezoresistive pressure sensor also called Solid State Pressure Sensor, have excellent electrical and mechanical stability that can be fabricated in a very small size.

Advantage:

  • Can eliminate the case-mounting effects on bias: Due to the small size of the pressure sensing silicon sensor, piezoresistive transducers may be constructed in a variety of packaging options that have been designed to eliminate the case-mounting effects on bias and sensitivity as well as low-frequency output generated by thermal expansion following proper installation. Piezoresistive SOI Sensors are fully integrated, monolithic structures.
  • Smaller size can do more jobs: The final form factor of a transducer is one of the more important device attributes for many customers. piezoresistive sensor technology offer more flexibility in packaging than any other technology due to the extremely small size of the sensing element. Automotive applications include engine air, oil, cooling and fuel systems, brake systems, transmissions and general laboratory/developmental pressure measurements. Typical aerospace applications are scale-model and full-scale flight tests. Scale-model wind tunnel test articles, for instance, require the measurement of pressures on leading edge portions of the airframe where the radius can be under one tenth of an inch. In other applications, pressure measurements must be made in areas where the test article thickness is very thin and cannot be penetrated. Only piezoresistive pressure transducers may be manufactured to small enough sizes to support either of these installations.
  • Extreme Environments Operability/Ruggedness: A majority of harsh environment commercial applications always use piezoresistive pressure transducers due to the small sensing element size (≈ 0.25 x 10-6 inch3 in volume), miniscule mass and robust construction. Piezoresistive pressure transducers do not require external amplifiers and special cables that other technologies need. Piezoresistive pressure transducers operate well in aircraft engine, nuclear, downhole, cryogenic, space, motor sports, and other extreme environment pressure measuring applications.
  • Good temperature compensation ability: piezoresistive pressure sensors may be conditioned by the use of embedded digitally-programmed electronics. The programmable analog sensor conditioner circuitry is paired with sufficient memory to linearize the piezoresistive pressure sensor to better than ±0.1% of full scale at a constant temperature. Since the bridge resistance changes predictably temperature and piezoresistive pressure sensors are extremely repeatable, the embedded electronics may also be used to correct for bias and sensitivity shifts due to temperature. Piezoresistive pressure transducer temperature sensitivity may be controlled to within ±0.001% of full scale per degree Fahrenheit after electronic characterization of thepressure sensor is programmed into the embedded conditioning electronics
  • Cost competitive: Installation costs of measurement systems dedicated to piezoresistive pressure transducers are generally lower than systems designed for piezoelectric pressure transducers. Transducers, cabling, and electronics for piezoresistive pressure transducers are each less than the cost of the corresponding piezoelectric pressure transducer system component. Fewer individual components are also a characteristic of piezoresistive pressure transducer installations.

Disadvantage of Piezoelectric-based sensing

Piezoelectric-based transducers rely on the piezoelectric effect, which occurs when a crystal reorients under stress forming an internal polarization. This polarization results in the generation of charge on the crystal face that is proportional to the applied stress2. Quartz, tourmaline, and several other naturally occurring crystals exhibit a piezoelectric effect. An electric charge proportional to the applied force is generated when a piezoelectric material is stressed by being coupled to an appropriate forcesumming device. Specially formulated ceramics can be artificially polarized to be piezoelectric with sensitivities 100 or more times higher than found in natural crystals3. Unlike strain gage sensors, piezoelectric sensors require no external excitation. These sensors exhibit high output impedance and low signal levels; therefore, piezoelectric devices require the use of special equipment such as low-noise coaxial cable and charge amplifiers in the measurement chain.

Disadvantage:

  • Susceptibility and inability: The high degree of stiffness provided by the compression mode enables the measurement of relatively high frequencies, but this construction worsens low frequency response due to thermally induced errors. Additionally, the compression mode construction is susceptible to a form of zero shift. Failure of the preload screw to maintain a constant force between the mass and the element will result in an output error. An abrupt change in the preload force may not be a one-time event and the resulting level shifts will be impossible to discern from pressure data.
  • Construction limitation: Pressure transducers constructed using the compression mode can also be quite sensitive to installation. Virtually all miniature piezoelectric pressure transducers are constructed within a threaded assembly or a case requiring a threaded mounting adapter. If excessive torque is applied during transducer installation or if the sealing surface is improperly machined, the body of the sensor may become distorted and the sensitivity of the device will be affected. All piezoelectric pressure sensors are susceptible to some degree of degraded performance as a result of excessive mounting torque. The user is expected take special precautions to apply the manufacturer-recommended torque during installation.
  • Big size if compare to piezoresistive technology: The smallest commercially available piezoelectric pressure transducer is 0.9 inches in length, 0.19 inches in diameter, and has an active sensing region 0.099 inches in diameter. However some isolated piezoresistive pressure transducer can be 0.375 inches in length, 0.055 inches in diameter, and having an active sensing element that is approximately 0.035” x 0.035”. This means that the smallest piezoresistive sensor is an order of magnitude smaller in volume, weight and sensing area than piezoelectric pressure sensor.
  • Invalid to absolute pressure measurement: Piezoelectric pressure transducers are incapable of absolute pressure measurement. Users may therefore be unaware they are operating in a region outside the recommended pressure range. For all pressure transducers, it is best to limit dynamic pressure to frequencies of 30% of resonance frequency. Approaching the diaphragm resonant frequency will result in erroneous data and may lead to diaphragm failure.
  • Accuracy decline in extreme temperature: All piezoelectric pressure transducers exhibit decreased insulation resistance when exposed to elevated temperature. This effect is due in part to the piezoelectric element, but the mineral insulated cable necessary to withstand the high temperatures typically contributes the largest error source. Specially constructed charge amplifiers must be used that are designed to operate with low impedance systems. These instruments capacitively couple the charge amplifier to the transducer/cable system to minimize the impact of potentially large offset voltages.

Features of Sputter deposited thin-film sensor

Sputter deposited thin film pressure sensor is a kind of Piezoresistive pressure sensors, difference exist that the thin-film sensor consists of a resistor pattern that is vaporized or sputter-deposited  onto the force-summing element (the measuring diaphragm). In some transducers the resistors are not directly mounted on the diaphragm but are on a beam linked to the diaphragm by a push rod.

Many applications use a manufacturing process known as thin-film sputtering deposition. The typical sputtering process uses an ion beam to impact the surface of a sputter material such as gold, silver, or other metal or metallic oxide. In so doing, some of the sputter-material atoms get knocked into free space. The atoms bond with a substrate material to form a thin coating that may be only a few atoms thick.

  • Integrity & Ruggedness: In the area of MEMS sensors, the sputtering-deposition technique lets manufacturers form sensors directly on the stressed substrate. The sensor becomes an integral part of the assembly, instead of being bonded to the stressed surface as are foil, resistive, and silicon strain gages. Combined with a Wheatstone bridge, thin-film sputtering-deposition strain gages eliminate many of the problems seen with these other measuring techniques, such as bonding separation or creep.
  • Sandwiched structure: Almost any material can be used as a substrate for the sensor including stainless steel, Inconel, Hastaloy, aluminium, sapphire, and titanium. The process begins by preparing the surface of the substrate with diamond slurry to remove all surface pinholes and cracks. A dielectric layer is first deposited on the substrate to insulate circuit power from the underlying metal. Then a thin film of resistive alloy is sputtered over the dielectric layer. This layer is laser trimmed under power to produce the balanced resistors of the Wheatstone bridge. Wires attached to bonding pads applied to the circuit provide power egress. An encapsulation layer coats the final assembly to protect the thin film.
  • Nearly perfect performance if made by sapphire: If made by sapphire, the sapphire pressure-gauge system is vacuum-filled and the resistor pattern forms a Wheatstone bridge. This system benefits from the elastic performance of the sapphire and its stable deformation properties. The result is a sensor with good repeatability, good stability, low hysteresis, and low drift. A high-gauge factor improves the resolution over traditional designs. The main disadvantages are low output level and high cost.