1. Definition and Function
A pressure transmitter is an instrument that converts physical pressure parameters (from gases or liquids) into electrical signals such as current, voltage, or digital outputs. These signals are transmitted to secondary instruments, including indicators, alarms, recorders, or controllers, for monitoring and process regulation.
Accurate range selection is one of the most critical factors in pressure transmitter application. An improperly selected range can not only reduce measurement accuracy but also significantly shorten the transmitter’s service life.
2. General Principle of Range Selection
In engineering practice, the maximum measuring range of a pressure transmitter should generally be 1.5 times the maximum system pressure.
When defining the range, the following conditions should be met:
The lower range limit should be less than or equal to the minimum operating pressure.
The upper range limit should be greater than the maximum operating pressure.
The normal working pressure should fall within 50–80% of the selected range.
Note: If the process pressure frequently approaches the upper limit, the transmitter may suffer from long-term overloading, resulting in accuracy drift and reduced lifespan.
3. Impact of Pressure Surges and Pulsations
In many process systems (especially water supply, hydraulic systems, or machining processes), pressure surges and pulsations are common. These transient peaks may:
Instantly exceed the transmitter’s rated range, damaging the sensing diaphragm.
Cause fatigue or shorten the service life when sustained high pressure occurs.
Mitigation Measures:
Install snubbers or buffer devices in the pipeline.
Select transmitters with integrated damping functions.
Ensure the overload pressure rating (typically 2× of the upper range) is sufficient.
4. Example of Range Definition
For a transmitter with a nominal range of 0–100 MPa:
The lower range limit (LRL) is 0 MPa (also called the zero point).
The upper range limit (URL) is 100 MPa (also called full scale).
The span or range is:
When applied in practice, if the system’s maximum working pressure is 60 MPa, then selecting a 0–100 MPa range would be appropriate to ensure safety and service life.
5. Conclusion
Proper range selection ensures that the pressure transmitter operates safely, provides accurate readings, and achieves its expected service life. Engineers should always:
Predict minimum, normal, and maximum operating pressures.
Select a range that accommodates pressure surges.
Avoid long-term operation near the transmitter’s upper limit.
By following these guidelines, pressure transmitters can deliver reliable performance in diverse industrial applications.