Pressure transmitter is the most commonly used transmitter in industry, which is widely used in various industries in automatic control environment. Here is a simple introduction to some common transmitter principles and their applications. 
Now let's take the wire strain resistance as an example. When the wire is subjected to external force, its length and cross-sectional area will change. From the above formula, it can be easily seen that the resistance value will change. If the wire is elongated by external force, its length increases, while the cross-sectional area decreases, the resistance value will increase. 
When the wire is compressed by external force, the length decreases and the cross section increases, and the resistance decreases. 
As long as the change added to the resistance (usually measuring two true voltages of the resistance) is measured, the strain condition of the strain wire can be obtained. 
The resistance of a metal conductor can be expressed by the following formula: 
R = ρ * Lhand S. 
In the formula: ρ-the resistivity of metal conductors (Ω? cm2/m). 
SMI-the cross-sectional area of the conductor (cm2). 
Lmure-length of the conductor (m). 
The two kinds of pressure of the measured medium of the pressure transmitter pass into the high and low pressure chambers, act on the isolation diaphragm on both sides of the δ element (that is, the sensitive element), and transmit to both sides of the measuring diaphragm through the isolation diaphragm and the filling liquid in the element. 
The measuring diaphragm and the electrodes on both sides of the insulating film each form a capacitor. 
When the pressure on both sides is inconsistent, it causes the displacement of the measuring diaphragm, and its displacement is proportional to the pressure difference, so the capacitance on both sides is different, and it is converted into a signal proportional to the pressure through oscillation and demodulation. 
The working principle of pressure transmitter and absolute pressure transmitter is the same as that of differential pressure transmitter, except that the pressure of low pressure chamber is atmospheric pressure or vacuum. 
The Ahand D converter converts the current of the demodulator into a digital signal, which is used by the microprocessor to determine the input pressure value. 
The microprocessor controls the work of the transmitter. 
In addition, it linearizes the transmitter. 
Reset the measurement range. 
Engineering unit conversion, damping, square, transmitter fine-tuning and other operations, as well as diagnosis and digital communication. 
This microprocessor has a RAM of 16-byte programs and three 16-bit counters, one of which performs A / D conversion. 
The Dhand A converter fine-tunes the corrected digital signals from the microprocessor, which can be modified by the transmitter software. 
The data is stored in EEPROM and remains intact even if the power is off. 
The digital communication line provides a connection interface for the transmitter with external devices, such as the 275 intelligent communicator or the control system using HART protocol. 
This line detects the digital signal superimposed on the 4-20mA signal and transmits the required information through the loop.