How to choose the pressure transmitter in the domestic chemical plant?

The selection of pressure transmitter includes the type, material, measuring range, explosion-proof performance and other aspects of the transmitter. Reasonable selection can not only ensure the service life of the transmitter, but also ensure the stable development of various processes in the chemical production process. 
The selection of transmitter is affected by many aspects, such as environmental conditions, application conditions, installation conditions, medium characteristics and economic benefits. 
The selection of transmitter and its application in chemical industry are briefly analyzed. 
1 Overview of the classification of transmitters. 
In the field of chemical application, pressure transmitter plays a very important role, and its application is also very extensive. 
There are many kinds of transmitters, which can be divided into absolute pressure transmitters, gauge pressure transmitters and differential pressure transmitters according to the measured objects. 

The isolated transmitter not only has the intima of the ordinary transmitter, but also has the outer membrane box which directly senses the pressure. the pressure felt by the external mold is transmitted to the intima through a stabilizing liquid, thus the pressure measurement value is obtained. the isolated transmitter is divided into integrated direct installation type and remote installation sealing type. 
According to the different environmental conditions, application conditions, installation conditions and other factors, the selection of the transmitter also has different requirements. 
2 selection of transmitter in different application fields. 

2.1 Type selection of transmitters in the field of pressure measurement. 
Transmitters are widely used in the field of pressure measurement, such as medium and low gauge pressure transmitters, medium and high gauge pressure transmitters, absolute pressure transmitters and medium and low gauge pressure single flange diaphragm sealed transmitters. 
According to the different methods of measurement and installation, the transmitter can be subdivided into two types: pipeline direct connection installation and pressure extraction installation of pressure guide tube. 
In the state of small pressure, the direct measurement of pressure may lead to unstable fluctuations, so when measuring the small pressure not higher than 500Pa, it is more reasonable to choose the differential pressure transmitter. 
2.2 selection of transmitter types in the field of differential pressure and liquid level measurement. 
The so-called differential pressure measurement refers to the pressure difference obtained by subtracting the pressure measured by the transmitter. 
In the field of liquid level measurement, the measurement results can be obtained by differential pressure measurement. 
The transmitters that can be used in the field of liquid level measurement are differential pressure transmitter, high differential pressure transmitter, flange mounted differential pressure transmitter and diaphragm sealed double flange differential pressure transmitter. 
When measuring the liquid level of an atmospheric vessel, it is appropriate to use a pressure transmitter or a single flange diaphragm sealed pressure transmitter because the vessel is connected to the atmosphere; when measuring the liquid level pressure of the sealed vessel, because there may be gas phase volatilization in the dense negative pressure chamber of the vessel, or nitrogen seal is used at the lower end of the container. 
Therefore, when measuring its hydraulic pressure, if the flange mounted transmitter is selected, the negative pressure chamber needs to guide the pressure tube connection, and if the diaphragm sealed transmitter is selected, then both positive and negative pressure chambers must be connected by remote flanges. 
For an open pool, if there is mud at the bottom, you can choose to use a single flange sealed diaphragm pressure transmitter to measure its liquid level. 
2.3 selection of transmitter types in the field of flow measurement. 
Flow measurement generally chooses differential pressure transmitter and diaphragm sealed double flange differential pressure transmitter, differential pressure transmitter needs to be equipped with orifice plate, Aniuba and Venturi and other throttling devices, and the measured result is also the value of differential pressure. 
If the medium such as steam or gas is measured, the flow value needs to be calculated through the quadratic table or DCS/PLC and other upper system. 
3 selection of transmitter under several special working conditions. 
3.1 High temperature environment. 
In the high temperature environment, the temperature of the measuring medium is high, the temperature of the process often exceeds the normal working range of the transmitter, and the temperature can not be adjusted to the normal range through the pressure guide tube or the installed isolation film. 
Then the remote transmission transmitter can be selected to use capillary pressure to prevent the high temperature of the transmitter from damaging the performance of electronic components. 
3.2 High viscosity working environment that is easy to crystallize. 
Once the medium leaves the process equipment, it is easy to crystallize. If crystallization occurs or the viscosity of the medium is too large, it is easy to lead to blockage of the guide tube, which not only needs to bring a large amount of work through cleaning and dredging, but also causes unstable measurement results. 
In this case, it is generally suitable to choose an isolated transmitter. 
If the crystallization phenomenon is serious, it is necessary to choose the convex diaphragm transmitter to directly obtain the temperature of the medium by inserting the pressure-sensitive diaphragm directly into the interior of the equipment. 
3.3 corrosive working environment. 
Corrosive condition generally refers to the corrosiveness of environmental conditions and application conditions. 
If the pressure guide tube is made of carbon steel or stainless steel, it is best to choose an ordinary differential pressure transmitter. 
In the corrosive working environment, there are certain requirements for the material of the transmitter, the most important of which are diaphragm and liquid material, flange material and shell material, etc., the diaphragm and liquid material should be selected according to the different chemical characteristics of the medium, the concentration and temperature of the medium are different, the requirements of the transmitter material are different. 
The transmitters with flanged links are generally made of carbon steel, 304SST and 316SST. Because the flanges are not directly connected with liquid, carbon steel is generally available for consideration of economic factors. 
The transmitter shell is generally made of aluminum alloy and stainless steel, so it is more economical to choose aluminum alloy in non-corrosive environment, and it is more suitable to choose stainless steel if it is in corrosive environment. 
4 conclusion. 
The transmitter is widely used in the chemical field. In the type selection, it is necessary to combine the chemical characteristics of the application environment, fully consider the comprehensive factors such as temperature, concentration, corrosion and so on, and then select the most reasonable type of transmitter by measuring its economy. to make it better meet the chemical production activities.