In order to do a good job in selecting pressure transmitters, we first need to understand what pressure transmitters are. What is the principle of pressure transmitters? ? ? Where is this meter suitable for? ? ? As the saying goes, “The skin will not be accompanied by a flukeâ€, only after these basic work is done well, the following selection work can be dealt with calmly. A pressure transmitter is a pressure sensor that uses the output as a standard signal. It is a meter that accepts a proportional change of the pressure variable to a standard output signal. It can convert the physical pressure parameters, such as gas and liquid, sensed by the load cell sensors into standard electrical signals (such as 4-20mADC, etc.) to provide secondary instruments such as alarm indicators, recorders, and regulators for measurement and indication. And process adjustments. The following describes the working principle of several pressure transmitters (in fact, almost all of them remain the same): 1. Strain gauge pressure transmitter The resistance strain gauge is a sensitive device that converts the strain change on the device under test into an electrical signal. It is one of the main components of a piezoresistive strain transmitter. The most widely used resistance strain gauges are metal resistance strain gauges and semiconductor strain gauges. Metal strain gauges are also available in wire strain gages and metal foil gages. Usually, the strain gauges are tightly bonded to a mechanical strain matrix through a special adhesive agent. When the stress of the base body changes, the strain gauges also deform together, so that the resistance of the strain gauges is changed, and thus The voltage applied to the resistor changes. Understand this, then we can learn about the selection section (note that the time for long knowledge is up): 1. What kind of media to measure: What we need to consider is the medium measured by the pressure transmitter. Viscous liquids and mud will block the pressure interface. Solvent or corrosive substances will not destroy the transmission. Materials in direct contact with these media. These factors will determine whether to select the direct isolation membrane and the material directly in contact with the medium. The material of the contact pressure medium part of the general pressure transmitter is made of 316 stainless steel. If your medium is not corrosive to 316 stainless steel, then basically all pressure transmitters are suitable for your measurement of medium pressure. If you The medium is corrosive to 316 stainless steel. Then we must use a chemical seal. This not only can measure the pressure of the medium, but also can effectively prevent the medium from contacting the wetted part of the pressure transmitter, thus protecting the pressure from changing. The transmitter extends the life of the pressure transmitter. 2. What kind of pressure range the transmitter should measure: First, determine the maximum pressure to be measured in the system. In general, it is necessary to select a transmitter that has a pressure range that is about 1.5 times larger than the maximum value. This is mainly because in many systems, especially in water pressure measurement and processing, there are peaks and continuous irregular up and down fluctuations. This momentary peak can damage the pressure sensor, the continuous high pressure value or a little beyond the transmitter. Calibrating the maximum value will shorten the life of the sensor, however, as this will reduce the accuracy. Thus, a buffer can be used to reduce pressure burrs, but this will reduce the sensor's response speed. Therefore, when selecting the transmitter, it is necessary to fully consider the pressure range, accuracy and stability. 3. Temperature range of the actual installation environment of the transmitter: Usually one transmitter will calibrate two temperature ranges, namely the normal operation temperature range and the temperature compensation range. The normal operation temperature range refers to the temperature range when the transmitter is not destroyed in the working state. When the temperature compensation range is exceeded, the application performance index may not be achieved. The temperature compensation range is a typical range that is smaller than the operating temperature range. Working within this range, the transmitter will certainly reach its proper performance. Temperature changes affect its output in two ways. One is zero drift; the other is affecting full-scale output. Such as: full scale / -X% / ℃, reading / -X% / ℃, when the temperature exceeds the full scale range / -X%, in the reading range of the temperature compensation / -X%, without these The parameters will lead to uncertainty in use. The degree to which the output of the transmitter changes is caused by a pressure change or a change in temperature. 4. How much precision the transmitter needs: decisive accuracy, nonlinearity, hysteresis, non-repeatability of the electromechanical business network, temperature, zero offset calibration, and temperature effects. But mainly by non-linear, hysteresis, non-repeating, the higher the precision, the higher the price. Each type of electronic meter will have an accuracy error, but because of the different levels of accuracy in each country, for example, the accuracy of national standards such as China and the United States is the best part of the linearity of the sensor, which is what we usually do. The accuracy of the measurement range is between 10% and 90%; while the accuracy of the European standard is the worst part of the linearity, which is what we commonly refer to as 0 to 10% and 90% to 100% of the inverse of the measurement. Accuracy between. Such as the accuracy of the European standard is 0.1%, and the accuracy of the standard in China is 0.5%. The pressure transmitter produced by the Anhui Tiankang Group can achieve an accuracy of 0.075%. 5 , what kind of output signal needed: mV, V, mA and frequency output digital output, choose what kind of output depends on many factors, including the distance between the transmitter and the system controller or display, whether there is "noise" or Other electronic interference signals. Do you need amplifiers, amplifier locations, etc. For many OEMs with short distances between transmitters and controllers, the most economical and effective solution is to use a mA output transmitter. If you need to amplify the output signal, it is best to use a transmitter with built-in amplification. For long-distance transmission or presence of strong electronic interference signals, it is best to use mA-level output or frequency output. In environments with high RFI or EMI specifications, besides noting that mA or frequency output should be selected, special protections or filters must be considered (the two-wire system currently used most in the market is 4- -20mA current output value). 6, according to the actual operating environment of the site to increase other selection parameters. Berlin Packaging (Qingdao) Co.,Ltd , https://www.berlinpackaging.cn
2, ceramic pressure transmitter pressure directly on the front surface of the ceramic diaphragm, so that the diaphragm produces a slight deformation, thick film resistors printed on the back of the ceramic diaphragm, connected into a Wheatstone bridge (closed bridge), due to The piezoresistive effect of the varistor causes the bridge to produce a highly linear voltage proportional to the pressure and a voltage signal proportional to the excitation voltage.
3, diffusion silicon pressure transmitter measured media pressure directly on the sensor diaphragm (stainless steel or ceramic), so that the diaphragm produces a proportional micro-displacement with the pressure of the medium, so that the resistance of the sensor changes, and use The electronic circuit detects this change and converts a standard measurement signal corresponding to this pressure.