Pressure Transducers General Description

Using 4-arm, 350-ohm bonded foil strain gage bridges, these tough stainless-steel transducers are designed for safe, accurate, and reliable electrical measurement of gas or fluid pressure in any number of industrial and research applications.

Daytronic provides the following pressure transducers:

  • Precision Gage / Absolute (502A Series: 1 - 15000 psi)
  • General-Purpose Gage / Absolute (512 Series: 10 - 10000 psi)
  • Low-Cost Gage (515A Series: 300 - 10000 psi)
  • Wet / Wet Differential (513 Series: 0.5 - 10000 psi)

Three Types of Pressure Measurement 

Gage Pressure

Gage pressure ("psig") is pressure measured relative to ambient atmospheric pressure (approximately 14.7 psi).  That is, a gage pressure measurement does not include atmospheric pressure itself.

For a gage pressure transducer, one side of the pressure-sensing diaphragm must be vented to the local environment.  The transducer will then indicate a pressure of "zero" when it is not connected to the process pressure of interest, but while the sensing element is still exposed to atmospheric pressure.

Gage pressure is actually a kind of differential pressure.  It always equals the difference between the local absolute pressure and the local atmospheric pressure.

Absolute Pressure

Absolute pressure ("psia") does include atmospheric pressure, and is measured relative to vacuum (0 psi).

For an absolute pressure transducer, the reference side of the pressure-sensing diaphragm is isolated from the local environment, being hermetically sealed in a vacuum.  (Absolute pressure sensors are thus not only isolated from environmental contaminants, but—theoretically—have better thermal performance than sealed gage units, because there is no trapped volume of gas to expand and contract with ambient temperature changes.)

The transducer will then indicate a pressure of 14.696 pounds per square inch at sea level, when it is not connected to the process pressure of interest, but with the sensing element exposed to atmospheric pressure.

Absolute pressure is always the sum of the local "gage" pressure (induced by some source) and the atmospheric pressure at the location of the measurement.

Differential Pressure

Differential pressure ("psid") is pressure measured relative to a specific reference pressure.  If the reference pressure is one atmosphere, the differential pressure equals the gage pressure.

Normally, a differential pressure transducer will have two pressure ports, and its pressure reading is generated by subtracting the pressure at the low port from that at the high port.  One port may be "dry" and the other "wet", or both may be "wet" (as with the Daytronic 513 Series), or both may be "dry."

Differential pressure may be either absolute or gage, as long as pressure is being measured in the same units at both ports.


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