What is a transducer?
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.
Why does non-electrical energy need to be converted into an electrical signal?
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.
What applications are transducers used for?
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:
What is Gauge Pressure?
What is Absolute Pressure?
What is Differential Pressure?
When is voltage output appropriate (AKA 0-5V, 0-10V, 0-20V)?
When is current output appropriate (AKA 4–20mA)?
What is “Transducer Accuracy?”
Probably the most common among pressure transducers are the strain gage base
transducers. Strain gages are bonded into the diaphragm of a pressure transducer,
then wired into a Wheatstone bridge configuration. When pressure is applied to
the transducer, it produces a deflection of the diaphragm which creates strain
on the gage. The physical deformation of the strain gage produces an electrical
resistance change proportional to the pressure, which is transmitted in an analog
electrical output signal which can then be read to determine amount of pressure.
Pressure transducers are available in 3 types of electrical output; millivolt (mV), amplified voltage, and 4-20mA.
Among the most economical of pressure transducers, the output of millivolt transducers is technically around 30mV. The actual output is proportional to the pressure transducer input power, also known as excitation. The output changes as the excitation fluctuates. Regulated power supplies are recommended for use with millivolt transducers because of this dependence on the excitation level.
Voltage output transducers provide a much higher output than millivolt transducers because they include *integral signal conditioning. Although model specific, output is typically 0-5Vdc or 0-10Vdc and is not usually a direct function of excitation. Because of this, unregulated power supplies can be sufficient as long as they are within a specified power range. Voltage output transducers are not as susceptible to electrical noise as millivolt transducers because they have a higher-level output, and therefore are more appropriate for use in industrial environments
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.
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