Introduction
A pressure transducer measures the pressure of gases or liquids. A pressure transducer generates an electrical signal as a function of the pressure applied.
Pressure transducer are used for control and monitoring in many applications. Pressure transducers can also be used to indirectly measure other variables such as fluid or gas flow, speed, water level, and altitude. Pressure transducers can alternatively be called pressure sensors and pressure transmitters.
Pressure transducers can be classified in terms of pressure ranges they measure, temperature ranges of operation, and the type of pressure they measure. In terms of pressure type, pressure transducers can be divided into several categories:
Gauge Pressure Transducer
The Gauge Pressure Transducer is used in different applications because it can be calibrated to measure the pressure relative to the atmospheric pressure. A water pressure gauge is an example of gauge pressure indication. When the water pressure gauge reads 0 Bar, there is really 1.01 Bar (atmospheric pressure) in the pipe.
Vacuum Pressure Transducer
The Vacuum Pressure Transducer is used to measure pressures less than the atmospheric pressure at a given location. This has the potential to cause some confusion as industry may refer to a vacuum sensor as one which is referenced to either atmospheric pressure (i.e. measure Negative gauge pressure) or relative to absolute vacuum.
Differential Pressure Transducer
The Differential Pressure Transducer measures the difference between two or more pressures introduced as inputs to the sensing unit, for example, measuring the pressure drop across a fan. Differential pressure is also used to measure flow or level in pressurized vessels.
Submersible Pressure Transducer
The Submersible Pressure Transducer is a transducer that is designed to operate below the surface of a liquid such as water. It is usually a gauge pressure transducer with a breather tube running up the electrical signal cable. The submersible transducer is used to measure the weight of the fluid at the point of measurement and can thus indicate the height of the fluid above the sensor.
The submersible pressure transducer is commonly called a level transducer or level sensor and can be used to measure the water level in a well.
Absolute Pressure Transducer
The Absolute Pressure Transducer measures the pressure relative to a perfect vacuum (0 Bar, 0 Pa). Atmospheric pressure, is 1.01 bar (101.3 KPa, 14.7 PSI) at sea level with reference to an absolute vacuum.
Pressure Sensing Technology
A pressure transducer, also known as a pressure sensor or pressure transmitter, is a device used to measure pressure and convert it into an electrical signal. The operation of a pressure transducer typically involves a sensing element that responds to changes in pressure and converts them into an output signal, which can be in the form of voltage, current, or frequency.
Here’s a general overview of how a pressure transducer works:
Sensing Element: The sensing element is the part of the transducer that directly interacts with the pressure being measured. It may consist of a diaphragm, strain gauges, piezoelectric material, or other mechanisms depending on the transducer’s design.
Pressure Application: The pressure being measured is applied to the sensing element, which deforms or changes its properties in response to the applied pressure. For example, a diaphragm may flex, strain gauges may change resistance, or piezoelectric materials may generate an electric charge.
Conversion Mechanism: The deformation or change in the sensing element’s properties is converted into an electrical signal. This conversion mechanism depends on the type of pressure transducer. Here are a few common types:
Strain Gauge: Some pressure transducers use strain gauges bonded to the sensing element. When pressure is applied, the strain gauges deform and change resistance, which can be measured using Wheatstone bridge circuitry to determine the applied pressure.
Piezoelectric: Piezoelectric pressure transducers utilize materials that generate an electric charge when subjected to mechanical stress. The pressure deforms the piezoelectric material, producing an electrical signal proportional to the applied pressure.
Capacitive: Capacitive pressure transducers employ a diaphragm or membrane that acts as one plate of a capacitor. The pressure causes the diaphragm to deflect, changing the capacitance between the diaphragm and a fixed plate. The change in capacitance is then converted into an electrical signal.
Vibrating Wire: Vibrating wire pressure transducers use a wire under tension that vibrates at its resonant frequency. When pressure is applied, it changes the tension on the wire, altering its resonant frequency, which is then measured as an electrical signal.
Signal Conditioning: The electrical signal produced by the conversion mechanism may be very small or require further processing. Signal conditioning circuitry is often used to amplify, filter, linearize, or otherwise manipulate the signal to meet the desired output requirements.
Output: The conditioned electrical signal is provided as an output from the pressure transducer. This output can be connected to various instruments or systems, such as data acquisition devices, control systems, or displays, for further analysis or utilization.
By measuring the changes in the electrical output, the pressure sensor enables accurate monitoring and control of pressure in a wide range of applications, including industrial processes, automotive systems, aerospace, healthcare devices, and many others.