Absolute pressure measurement refers to the pressure of a medium relative to absolute vacuum (0 pressure reference), which is different from gauge pressure that is referenced to atmospheric pressure.
Absolute pressure transmitters are widely used in vacuum systems, sealed tanks, gas pipelines, distillation towers, and process pressure monitoring applications where accurate pressure measurement relative to vacuum is required.
1. Working Principle of Absolute Pressure Measurement
The core component of an absolute pressure transmitter is the pressure sensing element, which may be capacitive, piezoresistive, or strain-gauge based.
The measurement principle is based on:
pressure acting on the sensing element → mechanical deformation → electrical signal conversion
Structure Characteristics
Inside the sensor, one side of the sensing diaphragm is exposed to the process medium pressure, while the other side is sealed against a vacuum reference chamber (0 absolute pressure).
This vacuum chamber provides a stable zero reference.
Signal Conversion
When process pressure acts on the sensing element, it causes physical deformation, such as:
- diaphragm displacement
- capacitance change
- resistance variation of strain gauges
The deformation is proportional to the applied absolute pressure.
The internal electronics convert this change into a standard output signal such as:
- 4–20 mA
- HART
- RS485 Modbus
Pressure Formula
The relationship is:
However, for an absolute pressure transmitter, this calculation is handled internally because the reference is already absolute vacuum.
2. Calibration Procedure for Absolute Pressure Transmitters
Proper calibration requires a vacuum calibration device or pressure calibrator capable of generating absolute pressure.
Step 1 – Preparation
Before calibration:
- isolate the transmitter from the process line
- release all process pressure
- ensure the pressure port is clean
- connect to a vacuum calibrator
- connect 24V DC power supply
- connect HART communicator
Step 2 – Zero Calibration
Apply:
This simulates absolute vacuum.
At this point, the output should be:
Perform zero calibration using the communicator.
Step 3 – Span Calibration
Apply the full-scale pressure.
For example, for a 0–1 MPa abs transmitter, apply:
The output should be:
Then perform span calibration.
Step 4 – Linearity Check
Check the following points:
- 25%
- 50%
- 75%
- 100%
Typical allowable error:
±0.5% FS
3. Common Fault Symptoms and Troubleshooting
This section is the most useful for customer search traffic.
1) Reading Too High or Too Low
Possible causes:
- zero drift
- span drift
- residual medium inside pressure chamber
- vacuum reference chamber leakage
Solutions:
- recalibrate zero and span
- clean the sensing chamber
- check vacuum chamber integrity
- return for repair if leakage is confirmed
2) Reading Fluctuates Severely
Possible causes:
- unstable process pressure
- loose sealing
- damping setting too low
Solutions:
- install pulsation damper
- tighten fittings
- increase damping to 3–5 seconds
3) No Signal Output
Possible causes:
- power supply failure
- wrong wiring
- damaged sensing element
- failed electronic board
Solutions:
- check 24V DC supply
- verify wiring polarity
- test with calibrator
- replace module if necessary
4) Output Does Not Change with Pressure
Possible causes:
- clogged pressure port
- diaphragm stuck
- medium solidification
Solutions:
- clean pressure port
- use suitable solvent
- replace diaphragm if permanently deformed
4. Typical Industrial Applications
Absolute pressure transmitters are commonly used in:
- vacuum pumps
- vacuum furnaces
- distillation columns
- gas storage tanks
- sealed reactors
- compressed gas systems
5. Need Help Selecting the Right Absolute Pressure Transmitter?
If you need assistance selecting an absolute pressure transmitter for your application, please share:
- pressure range
- process medium
- temperature
- process connection
- output signal
- hazardous area requirement
Our engineering team can recommend the most suitable model for your project.