Pressure measurement is critical in industries like HVAC, automotive, and manufacturing. However, confusion often arises when choosing between absolute, gauge, or sealed gauge pressure pressure sensors. If you only own a 10 bar/a absolute pressure pressure sensor, can you repurpose it and use absolute pressure sensor for gauge pressure at 9 bar or 10 bar?

Let’s break down the science, limitations, and practical steps to see whether it works?

Absolute vs. Gauge vs. Sealed Gauge: Key Differences

Absolute pressure represents the total pressure measured relative to a perfect vacuum (zero pressure), providing a fundamental reference point. This measurement technique is particularly valuable in scientific research and thermodynamic calculations where precise, standardized pressure assessments are essential.

Gauge pressure, conversely, measures pressure relative to the surrounding atmospheric pressure. This method is widely utilized in industrial and practical applications, offering a straightforward representation of pressure deviation from ambient conditions. Positive gauge pressure indicates pressure above atmospheric levels, while negative values suggest pressures below ambient atmospheric conditions.

Sealed gauge pressure represents a specialized subset of gauge pressure, where the reference point is a fixed, sealed volume at a specific environmental condition. This approach eliminates potential measurement variations caused by atmospheric pressure fluctuations, ensuring consistent and reliable pressure readings.

Take away:

• Absolute Pressure (bar/a): Measured relative to a perfect vacuum (0 bar).
• Gauge Pressure (bar/g): Measured relative to atmospheric pressure (~1 bar at sea level).
• Sealed Gauge Pressure (bar/sg): Similar to gauge pressure but referenced to a fixed atmospheric pressure (e.g., 1 bar), often used in sealed systems.

Can You Use an Absolute Pressure sensor for Gauge Pressure?

Short Answer: Yes, but with caveats.
To convert absolute pressure readings to gauge pressure:
Gauge Pressure = Absolute Pressure – Atmospheric Pressure

Theoretically, an absolute pressure sensor can be employed for gauge pressure measurement through mathematical conversion. By subtracting the current atmospheric pressure from the absolute pressure reading, one can derive the gauge pressure value.

However, this approach introduces potential complications and limitations.

• The primary challenges include atmospheric pressure variations, which can fluctuate due to environmental conditions such as altitude, temperature, and weather patterns.
• These variations can introduce measurement uncertainties and reduce the overall accuracy of the pressure reading.

Furthermore, the additional computational step required for conversion increases the complexity of the measurement process.

Scenario 1: Measuring 9 bar/g (Gauge)

• If your absolute pressure sensor reads 10 bar/a, subtract atmospheric pressure (~1 bar):
  10 bar/a – 1 bar = 9 bar/g
• But! Atmospheric pressure fluctuates with weather and altitude. For precise gauge measurement and readings, pair your pressure sensor with a barometric pressure sensor to dynamically adjust for atmospheric changes.

Scenario 2: Measuring 10 bar/g (Gauge)

• Your absolute pressure sensor’s maximum range is 10 bar/a, so:
  10 bar/a – 1 bar = 9 bar/g
• Problem: Measuring 10 bar/g would require an absolute reading of 11 bar/a, exceeding your pressure sensor’s 10 bar/a limit. This will be a little bit over-load (1.1X).

Scenario 3:  Measuring 10 Bar Gauge Pressure

Now let’s make assumptions as following

• Pressure sensors overload capability: 5× rated range(safely handles up to 15 bar absolute).
• Atmospheric pressure: 1 bar.
• Pressure sensor accuracy: ±1% of full scale (FS)(FS = 10 bar → ±0.1 bar error).

Absolute Pressure Calculation:

P_abs=P_gauge+P_atm=10 bar+1 bar=11 bar.

Pressure sensor Behavior:

• The pressure sensor’s rated rangeis 10 bar absolute, but its overload capacity allows it to survive up to 15 bar, so the pressure sensor will perform well if reach to 11bar;
• However, the accuracy is not guaranteed beyond the rated range 10 bar absolute(error may increase).

Accuracy Impact: At 11 bar absolute (10 bar gauge):

• If the pressure sensor’s output is linear, the error remains ±0.1 bar absolute(1% of FS).
• Absolute reading: 11±0.1 bar
• Gauge reading: (11−1)±1=10±0.1bar.
• Relative error for gauge pressure: ±0.1 bar/10 bar×100=±1% (same as FS error).

Scenario 4: Measuring 10 Bar Sealed Gauge Pressure

Absolute Pressure Calculation:

Sealed gauge assumes a fixed reference (e.g., 1 bar at sealing time).

P_abs=P_sealed+P_reference=10 bar+1 bar=11 bar.

Accuracy Impact:

Identical to gauge pressure measurement (see above Case).

Measures to Improve Measurement Accuracy

If an absolute pressure sensor is the only choice and device for you to measure gauge pressure, please you can refer to below measurers to improve measurement accuracy.

Dynamic Atmospheric Pressure Compensation:

• Add a separate atmospheric pressure pressure sensor to capture real-time atmospheric pressure for correction:
  Gauge Pressure = Absolute Pressure Pressure sensor Reading – Real-Time Atmospheric Pressure.
• If adding a pressure sensor is impractical, manually input the local average atmospheric pressure (sacrifices adaptability to environmental fluctuations).

Calibration Optimization:

• Recalibrate the pressure sensor for the high-pressure range (e.g., 8–11 bar) to improve linearity in the target zone.
• Use multi-point calibration (at least 3 points: 0 bar/a, 5 bar/a, 10 bar/a) and store an error compensation table.

Signal Processing Optimization

• Use a high-resolution ADC (e.g., 24-bit) to reduce quantization errors.
• If it is possible, apply software filtering (e.g., moving average, Kalman filter) to suppress noise.

Environmental Control:

• Stabilize pressure sensor temperature (temperature drift is a major error source).
• Avoid mechanical vibrations or shocks.

Critical Considerations

Overload ≠ Extended Range:

• Overload capability ensures safety, not accuracy. Pressure sensor accuracy is only valid within its rated range (10 bar absolute in this case).
• Beyond 10 bars, errors may increase due to non-linearity, hysteresis.

Calibration Dependency:

• If the pressure sensor’s output is recalibratedto interpret 11 bar absolute (e.g., scaling 0–15 bar to 0–10V), the ±0.1 bar error (1% FS) applies.
• Without recalibration, readings beyond 10 bar absolute are unreliable.

Practical Limitations:

• Most pressure sensors clamp their output at the rated FS (e.g., 4–20 mA transmitters stop at 20 mA for 10 bar).
• Example: A 10 bar absolute pressure sensor clamped at 10 bar would report 9 bar gauge, missing the true 10 bar gauge by 10%.

Overload Capacity Considerations

• The pressure sensor can withstand up to 15 bar absolute pressure, but prolonged operation at 11 bar (10 bar gauge pressure) may reduce lifespan. Recommend leaving a 20% margin (i.e., maximum measured value ≤ 12 bar absolute pressure).

Key Limitations:

• Near full-scale (10 bar/a), pressure sensor accuracy may degrade (e.g., increased nonlinearity).
• Deviations in atmospheric pressure (e.g., altitude or weather changes) will introduce errors unless dynamically compensated.

Does High Pressure Can Reduce Error?

Based on above discussion, one may ask that does High Pressure Reduce Error When Using Absolute Pressure sensors for Gauge/Sealed Gauge Measurements?

Short Answer: Yes, in most cases, using an absolute pressure pressure sensor to measure high gauge or sealed gauge pressures will result in lower relative error. Here’s why:

Example: Low vs. High Pressure Scenarios

Let’s compare two cases using a 10 bar absolute pressure sensor (±1% FS → ±0.1 bar error):

Case 1: Low Pressure (1 bar gauge)

• Absolute pressure: P_abs=1 bar (gauge)+1 bar (atm)=2 barP_abs​
• Gauge pressure: P_gauge=2 bar−1 bar=1 bar.
• Absolute error: ±0.1 bar.
• Relative error (gauge):

Case 2: High Pressure (9 bar gauge)

• Absolute pressure: Pabs=9 bar (gauge)+1 bar (atm)=10 barPabs​=9bar (gauge)+1bar (atm)=10bar.
• Gauge pressure: Pgauge=10 bar−1 bar=9 barPgauge​=10bar−1bar=9bar.
• Absolute error: ±0.1 bar (still fixed by FS).
• Relative error (gauge):

Result:

At 9 bar gauge, the relative error drops to ±1.1%—far lower than the ±10% error at 1 bar gauge.

So, using an absolute pressure pressure sensor for high gauge or sealed gauge pressures reduces relative error because:

1. The fixed full-scale error becomes a smaller fraction of the measured value.
2. Atmospheric pressure subtraction has minimal impact on high readings.

FAQ

Conclusion

You can use Absolute Pressure sensor for Gauge Pressure, because the pressure sensor can safely measure 10 bar gauge/sealed gauge pressure due to its 1.5× overload capability.

However:

• Accuracy degrades significantly if the pressure sensor clamps at URL of 10 bar absolute (10% error).
• If the pressure sensor is linear and recalibrated, the error remains ±1% FS (acceptable for many applications)