Pressure Transducers

A pressure transducer or sometimes referred to as a pressure transmitter, converts pressure into an analogue electrical signal. The conversion of pressure into an electrical signal is accomplished by the deformation of a strain gage, which is bonded into the diaphragm of the pressure transducer and wired into a Wheatstone bridge configuration. When pressure is exerted on the pressure transducer, the diaphragm deflects and produces an electrical resistance change proportional to the pressure. There are several types of pressure Transducers, which are available in three types of electrical outputs: 4-20mA, millivolt, and voltage and these three different types are described below.

The conversion of pressure into an electrical signal is achieved by the physical deformation of strain gages which are bonded into the diaphragm of the pressure transducer and wired into a wheatstone bridge configuration. Pressure applied to the pressure transducer produces a deflection of the diaphragm which introduces strain to the gages. The strain will produce an electrical resistance change proportional to the pressure.

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4-20 mA Output Pressure Transducers

4-20 mA output pressure transducers are ideal for use when the signal transmission is required over long distances because the 4-20 mA signal is least affected by noise or resistance in signal wires. 4-20 mA transducers are used commonly with applications, in which distances exceed 1000 feet.

Millivolt Output Pressure Transducers

Millivolt output pressure transducers are typically the most economical; however, because it has a low output signal, it is recommended to avoid locating the pressure transducer in an electrically noisy environment. In addition, it is recommended to keep the distance between the pressure transducer and the readout instrument relatively short. The millivolt output is nominally around 30mV and the output is proportional to the pressure transducer input power or excitation; therefore, if the input power or excitation fluctuates, the output of the pressure transducers will change as well. Due to this dependence between the input power and the output, it is suggested to use a regulated power supply with millivolt transducers for optimal performance.

Voltage Output Pressure Transducers

Voltage output pressure transducers contain integral signal conditioners, which provide a higher output than a millivolt transducer. Voltage output pressure transducers typically provide an output signal of 0-5Vdc or 0-10Vdc. For specific models, the output of the transducer is not a direct function of input power or excitation. Due to this independence between the input power and the output, unregulated power supply are sufficient generally as long as the power supply operates within a specified power range. Since voltage output pressure transducers have higher output levels, they are not as prone to electrical noise and operate better in electrically noisy industrial environments than millivolt transducers do.

Indication that a transducer was over pressurized

A common indication when a transducer is over pressurized is when there is a shift in the zero reading typically in an increasing direction – it may read 5-6 milliamperes (mA) or even higher and it can even saturate at a maximum value, typically around 24 milliamperes (mA).

Selecting the Appropriate Pressure Transducer

Pressure transducers or pressure transmitters are used in a variety of different industries.

Flush Diaphragm Pressure Transducers
For applications that require the monitoring of pressure on foods or very high viscosity liquids, flush diaphragm pressure transducers are optimal because the transducer diaphragm is flush to the process. This flushness eliminates the cavity above the diaphragm, which may collect fluid matter from the process and in certain applications, may be unfavourable.

General Purpose Transducers
The most common pressure transducers are general purpose transducers because they are designed to meet a multitude of application needs.

Heavy Duty/Industrial Pressure Transducers
Heavy duty/industrial pressure transducers are designed with a more rugged enclosure than other transducers to accommodate heavy industrial environmental applications. These types of pressure transducers feature a scalable 4-20mA output signal, which provide much greater immunity to electrically noisy industrial environments.

High Stability/High Accuracy Pressure Transducers
The accuracy of most pressure transducers are 0.25% or higher of full scale; however, high stability/high accuracy pressure transducers offer errors as low as 0.05% of full scale. High stability/high accuracy pressure transducers are more expensive than general purpose transducers but are the only option if high stability/high accuracy is required for your application.

PC Board Mountable Pressure Transducers
PC board mount pressure transducers are designed more compact in size than other transducers and are optimal for mounting on electrical PC boards or integrating into other products, in which size constraints are important.

Special Purpose Transducers
OMEGA offers a wide range of special featured pressure transducers and these transducers are designed to meet a host of application needs, such as pressure measurement in high or low temperature environments, measurement with digital communications output or wireless outputs, barometric pressure, and submersible pressure.