Pressure transmitters are field instruments that directly contact the measured medium. They often work in environments with high temperature, low temperature, corrosion, vibration, impact, etc. Therefore, when selecting pressure transmitters, in addition to considering the usual content that general instruments need to consider, such as measurement range and accuracy, the working environment and the measured medium are also important indicators. Generally speaking, the selection of pressure transmitters is mainly based on:
The measurement range of the pressure transmitter.
Generally, pressure (differential pressure) transmitters have a certain range that can be adjusted. It is best to set the range used in the 1/3 to 2/3 range of its range, which can ensure accuracy, especially for differential pressure transmitters. Determine the maximum pressure measured in the system. Generally, a transmitter with a pressure range that is about 1.5 times larger than the maximum value needs to be selected.
The accuracy level of the pressure transmitter.
Accuracy is a key performance indicator for any process measurement equipment and an important factor to consider when selecting and maintaining equipment. According to the pressure range, select the range first and then calculate the maximum allowable reference error of the instrument according to the maximum absolute error allowed in the process, remove the plus sign and percent sign, and the numerical value is the accuracy.
The measured medium of the pressure transmitter.
If the measured fluid is relatively clean, standard pressure transmitters can be directly used. If the measured medium is highly viscous, prone to crystallization, or highly corrosive, an isolated transmitter must be selected.
When selecting, consider the corrosion of the diaphragm box metal by the medium, and select the diaphragm box material carefully, otherwise the outer diaphragm will corrode and damage the equipment and cause personal accidents shortly after use. The diaphragm box materials of transmitters include ordinary stainless steel, 304 stainless steel, 316L stainless steel, and tantalum diaphragm box materials.
The liquid contact material of the pressure transmitter.
The material of the contact medium part of the general pressure transmitter is 316 stainless steel. If the measured medium does not corrode 316 stainless steel, then basically all pressure transmitters are suitable for measuring the pressure of the medium.
If the measured medium is corrosive to 316 stainless steel, chemical sealing must be used. This not only allows the pressure of the medium to be measured, but also effectively prevents the contact between the medium and the liquid-contacting part of the pressure transmitter, thereby protecting the pressure transmitter and extending its service life.
The medium temperature of the pressure transmitter.
Since the signal of the pressure transmitter is converted through the electronic circuit part, the measured medium temperature should be within the allowable range of the transmitter. When selecting a pressure transmitter, the maximum and minimum temperature of the measured medium should be taken into account, and a suitable transmitter should be selected according to the temperature range of the measured medium.