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How Does a Pressure Transducer Work?

A necessity in many industries, pressure transducers measure pressure and create an electrical output proportional to the input. This is done by using variable pressure sensors to measure deflection and resistance and transform that pressure into either a voltage, current or frequency.The sensing element or diaphragm is deflected due to input pressure and moves in relation to a resistor or capacitor plate that then sends an output signal based on the varying tension received by the input pressure. Most types of transducers require an electrical input called an excitation. Transducers typically produce one of three types of output: millivolt (mV), voltage (V), and milliampere (mA).

There are three main types of transducers: potentiometric pressure transducers, capacitance pressure transducers, and resonant wire pressure transducers. Potentiometric sensors are comprised of a precise potentiometer with an arm attached to a Bourdon or bellows. As the arm moves across the potentiometer, it converts the deflection into a measurement of resistance. These transducers are small in size and work great in tight spaces. They also produce a strong output, making them perfect for applications with low power. Capacitance sensors are sensitive and responsive; using a diaphragm transducer model to measure resistance. The diaphragm has a small space to travel, making it a valuable tool for low differential and absolute pressure applications. Resonant wire transducers measure pressure with a wire attached to the sensor diaphragm. Pressure changes affect the tension of the wire as it oscillates, changing the frequency at which the wire is resonating, and allowing for a more exact measurement. These transducers are ideal for low differential pressure applications.

Whichever pressure transducer you decide to use, it is important to remember two external variables that can inaccurately alter a trasnducer’s output signal: temperature and electromagnetic interference (EMI). As temperatures increase or decrease, there is a subsequent expansion or contraction in fluids and materials. This effect can change both the transducer’s mechanical and electrical properties and therefore alter its calibration. When high EMI field strengths are present, a transducer’s internal amplifier can become saturated and as a result cause inaccurate outputs. Shielding, grounding and routing techniques are implemented as a proactive measure to combat EMI interference.


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