A pressure measurement sensor, also called a pressure transducer or pressure sensor, converts an input mechanical pressure into an electrical output signal. There are a wide range of pressure transducer types on the market, each of which is classified by its size, capacity, measurement method, sensing technology, and output requirements. In this blog, we will provide a brief overview of pressure measurement sensors and their working principle.
Essentially, pressure transducers convert the input mechanical pressure in gasses or liquids into an electrical output signal. They consist of a pressure-sensitive element that can measure, detect, or monitor the pressure being applied, in addition to electronic components that convert the information into an electrical output signal. In general, pressure is defined as the amount of force exerted by a gas or liquid applied to a unit of “area” outlined by P=F/A.
Pressure utilizes the common units of pressure measurement, including Pascal (Pa), Bar (bar), N/mm2, or PSI (pounds per square inch). Moreover, pressure transducers frequently take advantage of piezoresistive technology, as the piezoresistive element changes their electrical resistance proportional to the strain (pressure) experienced. To better understand how pressure measurement sensors work, we will cover their working principle and piezoresistive effect.
Construction of a Pressure Transducer
In a pressure transducer, pressure is measured by a strain gauge of a metal foil variety and whose electrical resistance varies with applied pressure. Furthermore, pressure transducers use this gauge to convert force, pressure, tension, compression, torque, and weight into a change in electrical resistance that can be measured. In addition, strain gauges are electrical conductors that are tightly affixed to a film in a zigzag shape.
When the film the strain gauges are attached to is pulled, both the gauge and the conductors stretch and extend. When the film is pushed, it contracts and gets shorter. This change in shape makes the resistance in the electrical conductors change as well. Moreover, the strain applied in the pressure transducer is determined by this principle, as strain gauge resistance increases with applied strain and diminishes the contraction.
As previously mentioned, a strain gauge pressure transducer is composed of a metal body or flexure, wherein metal foil strain gauges are bonded. The body is typically made of aluminum or stainless steel, giving the sensor two key characteristics. The first being ample sturdiness to handle high pressures, and the second being sufficient elasticity to minimally deform when pressure is applied.
Three Types of Pressure Transducers
Pressure sensors can be categorized by the type of pressure measurements they gauge and the pressure-sensing technology they use. As such, there are three methods to measure pressure: differential, absolute, and gauge. In the next section, we will go over the aforementioned methods in more detail.
Differential Pressure Transducer:
Differential pressure is defined as the measurement of the pressure difference between two pressure values or two pressure points in the system. More specifically, differential pressure transducers measure how much the two points different from each other.
Absolute or Vacuum Pressure Transducer:
This sensor measures the absolute pressure which is the pressure measured in relation to a perfectly sealed vacuum. Absolute pressure sensors are often utilized where a constant reference is necessitated. For instance, high-performance industrial applications like monitoring vacuum pumps, liquid pressure measurement devices, industrial packaging, industrial process control, and more, use this technique.
Gauge or Relative Pressure Transducer:
Gauge pressure is a type of differential pressure where pressure can be measured differentially, but always relative to the local ambient pressure. Similarly, absolute pressure can also be considered a differential pressure, where the measured pressure is compared to a perfect vacuum. Keep in mind that atmospheric pressure changes caused by weather conditions or altitude have a direct effect on the output of the sensor. It is worth noting that if the measured pressure is below atmospheric pressure, it is referred to as negative or vacuum gauge pressure, whereas a gauge pressure higher than ambient pressure is called positive pressure.
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