Characteristics of Pressure Transmitters, Pressure Sensors and Pressure Transducers

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WIKA Instrument, LP

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Pressure Transmitters

Pressure Transmitters, a sub-group of pressure transducers, feature additional reset and calibration options. With some sensor types it is possible, for example, to re-set the measuring span over large ranges. This calibration option is usually referred to by such terms as “scale down”, “span reset” or “turn down”. For instance, a transmitter with a measuring range of 0 to 400 psi and a range reset 1/10 can be calibrate to a measuring range of 0 - 40 psi while still giving a full output signal (4 - 20 mA, for example).
 
It is also possible to shift the zero point over a wide range and to calibrate the damping of the output signal between 0 and 32 seconds. Smart transmitters such as Hart®, which also have logging capabilities, can be calibrated, tested and reset via the control desk or hand terminals.
 
Transmitters are often used in process applications where they can be combined with various chemical seals.

Pressure Sensors

Today many measuring principles are used in electronic pressure measurement instruments. Most methods are based on the measurement of a displacement or force. In other words, the physical variable “pressure” has to be converted into an electrically quantifiable variable. Unlike mechanical pressure measuring methods, this conversion requires an external power source for the pressure sensor.
 
This pressure sensor is the basis of electronic pressure measurement systems. While mechanical gauge element displacements of between 0.004 and 0.012 inches are standard, the deformations in electronic pressure sensors amount to no more than a few microns.
 
Thanks to this minimal deformation, electronic pressure measurement instruments have excellent dynamic characteristics and low material strain resulting in high resistance to alternating loads and long-term durability.
 
Listed below are pressure sensor technologies used by WIKA in its transmitter, transducer and sensor instruments:

  • Ceramic Thick Film Sensor
  • LVDT (Linear Variable Differential Transformer) Sensor
  • Piezoresistive (Piezo) Sensor
  • Thin Film Sensor

Pressure Transducers

Pressure transducers are an advanced form of the pressure sensor element. The simplest form of an electronic pressure measurement system is the pressure sensor. It is the pressure sensor which changes the physical variable “pressure” into a quantity that can be processed electronically. A pressure transducer is the next level of sophistication. In a pressure transducer, the sensor element and housing are in electrical contact and have a pressure connection.
 
Typical output signals from pressure transducers [WJ2] are between 10 mV and around 100mV, depending on the sensor type. These signals are not standardized, however, nor are they compensated. With thin-film type pressure transducers it is customary for just the sensor element to be welded to the pressure connection and then bonded electrically. Piezoresistive pressure transducers, on the other hand, require far more production steps since the semiconductor sensor element has to be protected from the effects of various media by a chemical seal.

Electronic Pressure Digest

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