Gauge, absolute and differential pressure
Gauge pressure is referenced to local atmospheric pressure. Absolute pressure is referenced to vacuum. Differential pressure (DP) is the difference between two process pressures. These quantities are not interchangeable.
How a pressure transmitter senses pressure
Many transmitters convert pressure-induced deformation of a diaphragm or sensing element into an electrical signal, then compensate and linearize the response electronically. Construction varies substantially by technology and application.
Differential pressure applications
DP measurement can infer filter condition, vessel level under defined conditions or flow through a primary element. The transmitter measures pressure difference; the final engineering quantity may require additional relationships and compensation.
The installation becomes part of the measurement
Process connections, impulse lines, seals, elevation differences, temperature and trapped gas or liquid can influence the value reaching the sensing element. That is why calibration at the bench cannot by itself prove the entire installed measurement loop is correct.
Range selection
A range should cover expected operation and credible excursions while still providing adequate measurement performance. Extreme over-ranging can reduce useful resolution; insufficient range can lead to saturation or overload risk.