The two pressures of the measured medium of the pressure transmitter pass into the high and low pressure chambers, acting on the isolation diaphragms on both sides of the delta element (ie the sensitive element), and transmitted to the measurement membrane through the isolation diaphragm and the filling liquid in the element Pieces on both sides. The electrodes on the measuring diaphragm and the insulating sheets on both sides form a capacitor.
When the pressure on both sides is inconsistent, the displacement of the measuring diaphragm is caused, and the displacement is proportional to the pressure difference, so the capacitance on both sides is unequal, and it is converted into a signal proportional to the pressure through oscillation and demodulation. The working principle of the pressure transmitter and the absolute pressure transmitter is the same as the differential pressure transmitter, the difference is that the low pressure chamber pressure is atmospheric pressure or vacuum.
The A / D converter converts the current of the demodulator into a digital signal, and its value is used by the microprocessor to determine the input pressure value. The microprocessor controls the work of the transmitter. In addition, it performs sensor linearization. Reset the measurement range. Engineering unit conversion, damping, prescribing, sensor fine-tuning and other operations, as well as diagnosis and digital communication.
There are 16 bytes of program RAM in this microprocessor, and there are three 16-bit counters, one of which performs A / D conversion.
The D / A converter fine-tunes the corrected digital signal from the microprocessor, which can be modified by the transmitter software. The data is stored in EEPROM, even if the power is turned off, it will be kept intact.
The digital communication line provides the transmitter with a connection interface with external devices (such as a 275 intelligent communicator or a 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.