The most common types of pressure transducers are strain gauge, and thick/thin film. Stain gauge transducers use the mechanical deformation under pressure of strain-sensitive variable resistors, which may be integrated into measurement circuits such as a wheatstone bridge. In a thick/thin film transducer, a titanium nitride or polysilicon film may be applied to sensing equipment to impart the circuit with piezoelectric sensitivity to pressure.
Almost all pressure transducers require a source of electrical input. The transducer input voltage can vary but typically falls under 10 V, while the output is typically in the hundreds of thousandths of volts. A change in the system’s pressure would cause a change in the transducer’s resistance on the electrical circuit and would result in a change to the output voltage. With the aid of an analog to digital converter (ADC), the transducer’s output signal can be used in systems that require digital signals.
For example, a programmable logic controller (PLC) or a programmable automation controller (PAC) can use the digital signal to monitor the pressure, and take action if needed. Some pressure transducers output current rather than voltage, and are then often referred to as transmitters. These values typically fall within tens of thousandths of amperes. When choosing the output of a pressure transducer it is important to keep in mind: the input requirements of the device that will be accepting the signal, the distance the signal must travel, and possible interference that can be found in the environment around the system.
Important performance criteria to consider are the pressure transducer: operating pressure range, max rated pressure, accuracy, and operating temperature range. The operating pressure range demarcates the intended pressure bounds at which the transducer has been designed to perform optimally. The max rated pressure is the highest allowable pressure that the pressure transducer is rated to withstand. The accuracy of the transducer is usually represented by suppliers in terms of ASME B40.1 grades: 4A (0.1%), 3A (0.25%), 2A (0.5%), A (1%), B (2%), C(3%), D (4%) deviance from the true pressure value. A good pressure transducers is designed to operate independently of temperature, however the operating temperature specifies a ‘safe’ range, outside of which temperature may significantly affect the accuracy of pressure sensing.
Specifying pressure transducers
Mechanism: What general mechanism is used to measure pressure?
Input-Output: What devices are powering the transducer, and what type of output is required to read from it?