Technical guidance on the use of pressure transmitters is shared and discussed

     The pressure transmitter is a field instrument that is in direct contact with the measured medium, and often works in high temperature, low temperature, corrosion, vibration, impact and other environments, so when selecting the pressure transmitter, in addition to considering the measurement range and accuracy and other general instruments that need to be considered, the working environment and the measured medium are also one of the important indicators. In general, the selection of pressure transmitters is mainly based on:

Generally, the pressure transmitter has a certain adjustable range, and the range used is set at 1/3~2/3 of its range, so that the accuracy will be guaranteed, which is more important for the micro-differential pressure transmitter. To determine the maximum value of the measured pressure in the system, it is generally necessary to select a transmitter with a pressure range that is about 1.5 times larger than the maximum value of the system. This is mainly due to the fact that in many systems, especially in water pressure measurement and processing, there are peaks and continuous irregular up and down fluctuations, and this instantaneous peak can destroy the pressure sensor. A shock absorber can then be used to reduce the pressure burr, but this will reduce the response speed of the sensor. Therefore, when selecting a transmitter, it is necessary to fully consider the pressure range, accuracy and stability.

    Accuracy is a key performance indicator for any process measurement equipment and an important factor to consider in equipment selection and maintenance. According to the pressure measurement range, according to the large error allowed in the process, the range is selected first, and then according to the large error allowed in the process, the large reference error allowed by the instrument is calculated, and the value of the ± number and % is removed. If there is no such level, it depends on the accuracy level (to rely on high accuracy). The accuracy level of pressure transmitters varies from country to country.

    However, the accuracy mentioned above is only an index provided by the pressure transmitter manufacturer, and in the actual application of the user's production site, if the overall performance error is expressed, only a very small part of the overall performance error in the actual application of the site may reach the index provided by the manufacturer, and in most cases the two are far from the same. In practical applications, the influencing factors mainly include the influence of the range ratio, the influence of temperature on the zero point, the influence of temperature on the range, the influence of static pressure on the zero point, and the influence of static pressure on the range.

In addition, the factors that affect the accuracy also include the influence of power supply, vibration, installation location, etc., but these factors have a relatively small impact and need to be considered according to actual needs.

If you are measuring a relatively clean fluid, you can simply use a standard pressure transmitter. If the measured medium is high viscosity, easy to crystallize and strongly corroded, a pressure transmitter must be selected. When storing and selecting the model, it is necessary to consider the corrosion of its medium on the metal of the diaphragm, and the material of the diaphragm must be selected, otherwise the outer diaphragm will be corroded after a short time after use, and the flange will also be

corroded and cause equipment and personal accidents. The material of the transmitter is ordinary stainless steel, 304 stainless

steel, 316L stainless steel, tantalum film box material, etc.

The material of the contact medium part of the general pressure transmitter is 316 stainless steel, if the measuring medium is not corrosive to 316 stainless steel, then basically all pressure transmitters are suitable for measuring the pressure of the medium.

If the measuring medium is corrosive to 316 stainless steel, then it is necessary to use chemical sealing, which can not only measure the pressure of the medium, but also effectively prevent the contact between the medium and the wetted part of the pressure transmitter, so as to protect the pressure transmitter and prolong the life of the pressure transmitter.

The signal of the ten pressure transmitter is converted by the electrical transmission line, so in general, the temperature of the measuring medium of the pressure transmitter is -30 to +100 degrees, if the temperature is too high, the condensation bend is generally used to cool the medium.

At present, due to the needs of various acquisitions, 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. However, the more commonly used ones are 420mA and 0~10V. Among the output signals listed above, only 4~20mA is a two-wire system including grounding or shielded wires), and the others are three-wire systems.

In practice, some applications (level measurement) require the transfer of the measuring range of the transmitter, which is calculated according to the installation location on site. At present, the intelligent transmitter has been quite popular, which is characterized by high precision, large adjustable range, and is very convenient to adjust, good stability, and should be considered more when selecting. In addition, the process connection interface of the pressure (differential pressure) transmitter as well as the supply voltage of the pressure transmitter should be considered explosion-proof and protection level if used in special occasions.