A transducer is an electronic device designed to convert one type of energy into a different type of energy. Non-electrical energy, such as pressure or temperature, can be converted into a quantifiable electrical signal using a transducer.
Transducers may also be referred to as “transmitters,” with the only functional difference being the type of electrical output; transducer output is measured in voltage, while transmitter output is measured in current. Whether the use of a transducer or a transmitter is appropriate is determined by the overall needs of the intended final application.
Once converted into electronic signal, pressure and temperature measurements can be integrated into software programs that enable report generation, the remote or automated monitoring of environmental conditions, or integration into a larger system of variables.
Transducers are a core functional component across nearly all major industries, including Oil and Gas, Aerospace, and Automotive. They provide the means for fuel regulation, altitude control, and temperature control, among countless other applications.
When deciding what type of pressure transducer to use for a specific application, a number of factors need to be considered. Among these are:
“Differential Pressure” transducers compare the quantity of two separate medias without using a definitive set reference point (such as atmospheric pressure or vacuum). For example, a transducer may act as a filter monitor by comparing the pressure increase caused by contaminant build-up to the pressure level established upon installation. Measurements will be labeled in PSIG.
Hysteresis is defined fairly universally (I say “fairly” because there will ALWAYS be the possibility of exceptions, so it’s important to be aware of that possibility so that any miscommunication between manufacturer and customer are avoided):
As pressure is applied to a sensor, this is referred to as “increasing pressure.” When pressure is removed from a sensor, this is referred to as “decreasing pressure.” Hysteresis is determined by measuring output points at predefined intervals during increasing pressure, and comparing them to output points measured at the same predefined intervals during decreasing pressure. The maximum difference found between the increasing pressure points and the decreasing pressure points is the hysteresis value of the transducer, and is mathematically defined as a percentage of the full-scale output of the sensor.
Repeatability is well-defined as the maximum difference in output when the same pressure is applied, consecutively, under the same conditions and approaching from the same direction.
Pressure transducers are available in 3 types of electrical output; millivolt (mV), amplified voltage, and 4-20mA.
Also known as pressure transmitters, a 4-20mA transducer is least affected by electrical noise and resistance in the signal wires, and is therefore best suited for when a signal must be transmitted long distances. 4-20mA transducers are commonly used in applications where the lead wire must be 1,000 feet or more.
*Most analog signals require some form of preparation before they can be digitized. Signal conditioning is the manipulation of a signal in a way that prepares it for the next stage of processing. Many applications involve environmental or structural measurement, such as temperature and vibration, from sensors. These sensors, in turn, require signal conditioning before a data acquisition device can effectively and accurately measure the signal. For example, thermocouple signals have very small voltage levels that must be amplified before they can be digitized. Other sensors, such as resistance temperature detectors (RTDs), thermistors, strain gages, and accelerometers, require excitation to operate. All of these preparation technologies are forms of signal conditioning.