1. What is Pressure Sensor?
Pressure sensors are devices used to measure pressure and convert pressure into electrical signals. The signal is transmitted to the display, the controller or the PLC
The output signal of the pressure sensor can be either a digital signal (NPN / PNP) or an analog signal (0 ~ 10V, 4 ~ 20mA, …)
2. Structure and working principle of pressure sensor
2.1 Structure
Structure of pressure sensor consists of 2 main parts:
+ Sensor: the part that receives signals from pressure and transmits signals to the processing unit. Depending on the type of sensor, it switches from the mechanical signal of pressure to resistor signal form, capacitance, inductance, current … to the processing unit.
+ Processing unit: has the function of receiving signals from the sensor unit performing the processing to convert those signals into standard signals in the field of pressure measurement such as output voltage signal 4 ~ 20 mA (most commonly used signal), 0 ~ 5 VDC, 0 ~ 10 VDC, 1 ~ 5 VDC), NPN/PNP.
Depending on the type of sensor is also different ways of operation, people classified pressure sensors include three main types: strain gage based, variable capacitance, piezoelectric
2.2 Working Principle
According to the diagram above, we see that when the positive pressure (+) is applied, the membrane will stretch from left to right, and when applying negative pressure (-), the membrane will stretch from right to left. It is this shift that will send the signal to the processing circuit and signal to know how much pressure is in.
- The first picture on the left: When there is no pressure => Hight = Low = 0V Output
- The middle picture: When there is compression pressure => High > Low = + V Output
- Right picture: When there is suction pressure => Low> High = – V Output
The membrane of the sensor will contain very small sensors to detect the change. When an applied force is applied, the membrane is changed in the direction that corresponds to the force. The sensor then compares the change to the original to know how much %
>>> the corresponding output signal will be output. The output signal can be 4-20ma or 0-10V corresponding to the input pressure.
3. Application of pressure sensors
- Pressure gauge for water, compressed air, hydraulics, gas, pressure for other liquids
- Pressure sensors for measurement in the boiler system, usually measured directly on the boiler. This area needs to be measured fairly accurately and must withstand high temperatures.
- Gas machines also need to measure the pressure to limit the outlet pressure, avoiding over-pressure leading to damage & fire.
- On the water pump stations also need pressure sensors to monitor the pressure brought to the PLC or Inverter to control the water pump.
- To control or control the pressure after the control valve, the pressure sensor plays a very important role because it will directly affect the outlet pressure behind the control valve.
- Pressure sensors used for gasoline, oil, … oil and gas industry must ensure explosion-proof standards.
Basic parameters to keep in mind when choosing a pressure sensor
- Purpose of using pressure sensor: Measure the pressure of water, compressed air, chemicals, …
- Sensor working environment: What is temperature and humidity
- Output signal of pressure sensor (normally 4-20mA)
- What is the pressure scale? What is the maximum bar pressure limit on the pipe?
- Allowable error of pressure sensor to be measured
- Response time
- How much does the sensor operate at?
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