Pressure sensor/transmitter selection Guide
1, the transmitter to measure what kind of pressure: First determine the maximum value of the measured pressure in the system, in general, you need to choose a transmitter with a pressure range about 1.5 times larger than the maximum value. This is mainly due to the fact that in many systems, especially in hydraulic measurement and processing, there are peaks and continuous irregular fluctuations up and down, this instantaneous peak can destroy the pressure sensor, and continuous high pressure values or slightly beyond the calibration maximum of the transmitter will shorten the life of the sensor, however, because of the reduction in accuracy. Therefore, a buffer can be used to reduce the pressure burr, but this will reduce the response speed of the sensor. Therefore, when choosing a transmitter, it is necessary to fully consider the pressure range, accuracy and stability.
2, What kind of pressure medium: We have to consider the medium measured by the pressure transmitter, viscous liquid, mud will plug the pressure interface, solvent or corrosive substances will not destroy the material in direct contact with these media. These factors will determine whether to choose a direct isolation film and a material in direct contact with the medium. The general pressure transmitter contact medium part of the material is 316 stainless steel, if your medium is not corrosive to 316 stainless steel, then basically all the pressure transmitters are suitable for your measurement of medium pressure. If your medium is corrosive to 316 stainless steel, then we must use a chemical seal, so that not only can measure the pressure of the medium, but also can effectively prevent the contact between the medium and the liquid part of the pressure transmitter, so as to protect the pressure transmitter and extend the life of the pressure transmitter.
3, how much accuracy the transmitter needs: determine the accuracy of non-linearity, hysteresis, non-repeatability, temperature, zero bias scale, temperature influence. But mainly by nonlinear, hysteresis, non-repeatability, the higher the accuracy, the higher the price. Each kind of electronic measuring meter will have accuracy errors, but because the accuracy level of each country is not the same, for example, the accuracy of China and the United States and other countries is the best part of the linearity of the sensor, that is, the accuracy of the measurement range we usually say between 10% and 90%; The accuracy of the European target is the worst part of linearity, that is, we usually say that the accuracy of the measurement is between 0 and 10% and 90% to 100%. If the accuracy of the European target is 1%, the accuracy of the target in China is 0.5%.
4, the temperature range of the transmitter: usually a transmitter will calibrate two temperature ranges, that is, the temperature range of normal operation and the temperature can be compensated. The normal operating temperature range refers to the temperature range when the transmitter is not damaged in the working state, and when it exceeds the temperature complement range, the performance index of its application may not be reached. The temperature compensation range is typically a smaller range than the operating temperature range. Working in this range, the transmitter will certainly reach its due performance indicators. Temperature change affects its output from two aspects, one is zero drift; Second, it affects the full scale output. For example: full scale +/-X%/℃, reading +/-X%/℃, full scale +/-X% when outside the temperature range, reading +/-X% when within the temperature compensation range, without these parameters, will lead to uncertainty in use. Whether the change in the output of the transmitter is caused by a change in pressure or by a change in temperature. Temperature effects are the most complex part of understanding how to use a transmitter.
5, need to get what kind of output signal: mV, V, mA and frequency output digital output, choose what kind of output depends on a variety of factors, including the distance between the transmitter and the system controller or display, whether there is “noise” or other electronic interference signals. Whether the amplifier is needed, the position of the amplifier, etc. For many OEM devices with a short distance between the transmitter and the controller, the transmitter with mA output is the most economical and effective solution, and if the output signal needs to be amplified, it is best to use a transmitter with built-in amplification. For long-distance transmission or strong electronic interference signals, it is best to use mA level output or frequency output. In an environment with high RFI or EMI indicators, special protection or filters should be taken into account in addition to the mA or frequency output to be selected. (At present, due to the needs of various collection, there are many kinds of output signals of pressure transmitters on the market, mainly 4… 20mA,0… 20mA,0… 10V,0… 5V and so on, but the more common one is 4… 20mA and 0… Two kinds of 10V, in these output signals I mentioned above, only 4… 20mA is a two-wire system, we say that the output is a few wire system does not include ground or shielded wire, the other are three-wire system)
6, choose what excitation voltage: the type of output signal determines what excitation voltage to choose. Many amplifying transmitters have a built-in voltage regulator, so their supply voltage range is large. Some transmitters are quantitative configurations that require a stable operating voltage, so the available operating voltage determines whether to use a sensor with a regulator, and the operating voltage and system cost should be considered comprehensively when choosing a transmitter.
7, whether you need to have an interchangeable transmitter: determine whether the required transmitter can adapt to multiple use systems. In general, this is important. Especially for OEM products. Once the product is delivered to the customer, the cost of calibration for the customer is considerable. If the product has good interchangeability, then even changing the transmitter used will not affect the effect of the entire system.
8, the transmitter needs to maintain stability after overtime work: most transmitters after overtime work will produce “drift”, so it is necessary to understand the stability of the transmitter before purchase, this advance work can reduce the future use of all kinds of trouble.
9, transmitter packaging: the packaging of the transmitter, in particular, is often easy to ignore its rack, however, this point will gradually expose its shortcomings in future use. In the purchase of the transmitter transmission must take into account the future working environment of the transmitter, how humidity, how to install the transmitter, will there be strong impact or vibration.
10, what kind of connection is used between the transmitter and other electronic equipment: Is it necessary to use short-distance connection? Do you need a connector for long distance connections?