Sensor Technology Pressure Transducer Basics
Jim Furness
A pressure transducer is an electro mechanical device which is used to measure the pressure in an environment or process, and output an electrical signal as an analogue of the measured value.
There are many types of pressure transducer used in industry, with varying measurement ranges, performance, and size, depending on the application. The main types of pressure transducer can be summarized as follows:
Capacitive pressure transducer In capacitive technology, the pressure diaphragm is one plate of a capacitor that changes its value under pressure-induced displacement.
Piezoresistive pressure transducer This consists of a pressure diaphragm fitted with fixed resistors. Under the pressure-induced strain, the resistors change their value. The resistors are arranged in a Wheatstone bridge and this produces a voltage output proportional to pressure
For most industrial applications the piezoresistive pressure transducer is ideal. Typical size is no more than 80mm long by 25mm diameter, with measurement ranges from vacuum up to 2200 bar, and accuracy up to 0.1% of full scale range.
What sort of process measurements would a pressure transducer be used for ? The applications are very varied but the most common one would be:
Compressed Air Many factories use compressed air around the site and a pressure transducer may be fitted at several places to ensure that system pressure is maintained.
Hydraulics The pressure transducer is used to monitor fluid pressure in actuators and brake lines.
Water Level Measurement The pressure transducer is used to measure liquid level in reservoirs and tanks
Oil Production Here many types of pressure transducer are used to monitor wellhead pressure and system pressure throughout the production process.
Water treatment Works Pumping units are often fitted with a pressure transducer to monitor pump performance.
Typical Specifications A standard industrial type pressure transducer will normally be of stainless steel construction with either ceramic or stainless steel diaphragm. The most common pressure transducer connection is ﾼ BSP male thread, although ﾽ BSP and NPT threads are also popular. Typical pressure transducer outputs are 0-5v DC, 0-10v DC, 0-100 mV DC, and 4-20mA. A pressure transducer with a 4-20mA output is sometimes referred to as a pressure transmitter. Accuracy will vary from 1-2% of full scale for a low cost pressure transducer for use in non critical applications to as high as 0.05% where accuracy is paramount.
Pressure Transducer Selection When selecting a pressure transducer for a given application the following criteria should be considered:
Operating pressure range Output type required Accuracy required Burst pressure Mechanical fitting required Operating temperature
The latest developments in pressure transducer technology offer increased accuracy, smaller size and serial outputs for automotive applications. With the ever increasing demand for pressure measurement in industry, research and manufacturing, the market for all types of pressure transducer are set to increase for many years to come. ----------
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About The Author
Jim Furness is CEO of Omniinstruments Ltd, specialists in pressure transducer and other instrumentation solutions such as ultrasonic flow meter.
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