Views: 86 Author: Site Editor Publish Time: 2020-03-03 Origin: Site
In the last article, we learned about the definition and classification of pressure sensors. Next, we need to understand the wiring method and working principle of pressure sensors, so that we can understand pressure sensors more deeply.
Sensor wiring has always been one of the most consulted questions in the customer procurement process. Many customers do not know how to connect the sensors. In fact, the wiring methods of various sensors are basically the same. Pressure sensors generally have two-wire, three-wire, four-wire system, and some five-wire system.
The pressure sensor two-wire system is relatively simple, so most customers know how to connect: one line is connected to the positive pole of the power supply, and the other line is the signal line connected to the negative pole of the power through the instrument. A wire is added to the two-wire system. This wire is directly connected to the negative pole of the power supply, which is a bit more troublesome than the two-wire system. The four-wire pressure sensor must have two power input terminals and the other two signal output terminals. Most of the four-wire system is a voltage output instead of a 4-20mA output. A 4-20mA is called a pressure transmitter, and most of them are made of a two-wire system. Some of the signal output of the pressure sensor is not amplified, the full-scale output is only tens of millivolts, and some pressure sensors have an internal amplification circuit, and the full-scale output is 0 ~ 2V. As for how to connect the display meter, it depends on the range of the meter. If there is a gear that is suitable for the output signal, you can directly measure it, otherwise you need to add a signal adjustment circuit. The five-wire pressure sensor is not much different from the four-wire system, and there are relatively few five-wire sensors on the market.
There are many types of pressure sensor threads. The more common ones are NPT, PT, G, and M, all of which are pipe threads. This item will not go into the detailed classification. We only need to know that the pipe thread is mainly used for the connection of pressure pipes. The internal and external threads are closely matched. There are two types of pressure sensor pipe threads: straight and tapered. The nominal diameter refers to the diameter of the connected pressure pipe. Obviously, the larger diameter of the thread is larger than the nominal diameter.
There are the working principles of several different types of pressure sensors.
The resistance strain gauge is one of the main components of a piezoresistive strain sensor. The working principle of metal resistance strain gauges is the phenomenon that the resistance of the strain resistance absorbed on the base material changes with the mechanical deformation, which is commonly known as the resistance strain effect.
The ceramic pressure sensor is based on the piezoresistive effect. The pressure directly acts on the front surface of the ceramic diaphragm, causing the membrane to deform slightly. The thick film resistor is printed on the back of the ceramic diaphragm and connected to form a Wheatstone bridge. The piezoresistive effect makes the bridge generate a voltage signal that is highly linear and proportional to the pressure and proportional to the excitation voltage. The standard signal is calibrated to 2.0 / 3.0 / 3.3mV / V according to the different pressure ranges. Strain sensors are compatible.
The working principle of diffused silicon pressure sensors is also based on the piezoresistive effect. It uses the principle of piezoresistive effect. The pressure of the measured medium directly acts on the diaphragm of the sensor (stainless steel or ceramic), causing the diaphragm to generate a micro-displacement that is proportional to the pressure of the medium. This change is detected and a standard measurement signal corresponding to this pressure is converted and output.
Utilizing the strain-resistance principle and using silicon-sapphire as a semiconductor sensitive element, it has unparalleled metrological characteristics. Therefore, semiconductor-sensitive components made of silicon-sapphire are not sensitive to temperature changes, and have good working characteristics even at high temperatures; sapphire has very strong radiation resistance; In addition, silicon-sapphire semiconductor-sensitive components, no p-n drift.
Piezoelectric effect is the main working principle of piezoelectric sensors. Piezoelectric sensors cannot be used for static measurement, because the charge after external force is only saved when the loop has infinite input impedance. This is not the case, so this determines that piezoelectric sensors can only measure dynamic stress.
After the tire pressure monitoring system is installed on a vehicle tire, the tire pressure detection sensors of each tire need to be matched. The matching includes, but is not limited to, identifying the tire pressure sensor installation position, identifying the tire pressure sensor ID, the tire pressure sensor and the tire pressure receiving module Communication, etc.
