What Is a Differential Pressure Sensor?
A differential pressure sensor is a pressure sensor used to measure the difference in pressure between two points connected to a sensor.
The purpose of a differential pressure sensor is to measure the difference between two points. Therefore, it does not matter whether the pressure to be measured is atmospheric, negative, or fluid pressure. In addition, since differential pressure sensors do not measure absolute values, the device itself is relatively small, and many inexpensive products are available.
Another feature of differential pressure sensors is that they can be easily calibrated.
Uses of Differential Pressure Sensors
Differential pressure sensors are general-purpose sensors and are widely used in various fields of industry. The main applications are anemometers and air conditioning equipment.
In industrial equipment, they are also used to monitor the operating status of pumps, compressors, and other equipment, as well as to monitor filter clogging. A typical example of a filter-clogging application is in diesel engines for automobiles.
Diesel engines are equipped with a diesel particulate filter (DPF), which removes particulate matter emitted from the diesel engine. A differential pressure sensor is used to measure the particle build-up in the DPF.
In addition, it is also useful for measuring the volume of liquid in tanks. The structure of the differential pressure sensor can also be used to measure the differential pressure between different phases (forms), such as the liquid in the tank and atmospheric pressure.
Principle of Differential Pressure Sensors
Differential pressure sensors can be broadly classified into two types: those using strain gauges and those using capacitance sensors. The principle of measurement is the same for both types of sensors, utilizing the deformation of a diaphragm caused by the difference in pressure between two points. The method used to measure the amount of deformation (strain) of the diaphragm is selected according to the characteristics of each method.
1. Using a Strain Gauge
In the method using strain gauges, a strain gauge is attached to a diaphragm and the change in resistance of the strain gauge due to deformation of the diaphragm is measured. Since there is almost no change in resistance over time, this type of sensor is suitable for long-term, static force measurement applications.
2. Using a Capacitance Sensor
In those using a capacitance sensor, the distance between two electrodes placed on a diaphragm changes as the diaphragm deforms, resulting in a change in the capacitance between the electrodes. The capacitance sensor measures the amount of this change in capacitance.
Although differential pressure sensors using capacitance sensors structurally change their output values slightly over time, they tend to be robust to dynamic measurements because of the high rigidity of the sensor housing and its high natural frequency.
Other Information on Differential Pressure Sensors
1. Types of Pressure in Pressure Measurement
There are three types of pressure measured by various measuring instruments. It is helpful to correctly remember the meaning and relationship of each value.
Absolute Pressure
Absolute pressure is the pressure relative to an absolute vacuum. An absolute vacuum is a state in which there is no matter in a certain space.
Gauge Pressure
Gauge pressure is the pressure relative to atmospheric pressure. Since atmospheric pressure also changes with location and time, gauge pressure changes with location and time even if the measured value is the same.
Differential Pressure
Differential pressure is the difference between the pressure at a certain location and a standard. Therefore, when measuring differential pressure, the reference pressure must always be measured as a set in addition to the object of measurement.
2. How to Measure Gauge Pressure With a Differential Pressure Sensor
A differential pressure sensor is a device that measures the difference in pressure between two points. One can measure atmospheric pressure and the other can measure gauge pressure.
To measure gauge pressure with a differential pressure sensor, it is common to connect the HIGH side of the differential pressure sensor to the object whose gauge pressure is to be measured and leave the LOW side open to the atmosphere.