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Pressure Limits

 

Non-Differential Transducers

For a standard, single ended pressure transducer (psia, psig, etc.) there are three or four pressure limits of importance, depending on the design purpose of the instrument.

Pressure Range - The values within which the instrument is designed to measure, specified by its lower and upper limits (e.g. 0-500 psi, 13-16 psi, etc.).  To provide a margin of safety, transducers are often selected so the system operating pressure is approximately 60% of the transducer's maximum pressure rating.

Proof Pressure - Also referred to as the "over-range capacity", this is the maximum specified pressure which may be applied to the sensing element of a pressure transducer without causing a permanent change in the output characteristics (e.g. a zero shift beyond specified tolerance).  The proof pressure can be expressed as a specific pressure limit or as a multiple of the upper range value.

Burst Pressure* - The maximum fluid pressure that may be applied to the transducer's pressure cavity without causing leakage of the fluid being measured from the pressure cavity.  In some cases, burst pressure may pertain instead to a down line secondary containment or to the transducer body itself. 

External Case Pressure - For submersible transducers, the maximum pressure (depth of water) supported by the transducer body, pressure port, and electrical receptacle (example: 15,000 psi = 34,566 ft. of seawater).

* elsewhere known as "bursting pressure"

 

Differential Transducers

Differential pressure transducers (psid, psiud, psibd) have similar limits that are expressed in a slightly different manner.

Pressure Range - Those values within which the pressure transducer is designed to measure. An example is 0-10 psid (10 psiud or psiu; or psi unidirectional) or ± 5 psid (5 psibd or psib; psi bidirectional).

Differential Overload (Proof Pressure) - This is the maximum allowable difference in pressure between the two pressure ports, without causing a permanent change in the output characteristics of the transducer (i.e. zero shift beyond specified tolerance).

Rated Line Pressure - This is the maximum static pressure that can be supported by both differential ports simultaneously. The maximum line pressure and the differential overload pressure are sometimes the same or very close.

Burst Pressure - The maximum pressure applied to the pressure ports, either simultaneously or separately, without causing leakage of the fluid being measured from the pressure cavity.