Liquid level transmitter is an extension and development of pressure transmitter technology. According to the principle that the pressure generated by liquids of different specific gravity at different heights is linear, the volume, liquid height and weight of water, oil and paste can be accurately measured and transmitted.
The liquid level transmitter working principle is that when the two kinds of pressures of the measured medium are passed into the high- and low-pressure chambers, they act on the isolation diaphragms on both sides of the δ element (that is, the sensitive element), and then it is transmitted to both sides of the measuring diaphragm through the spacer and the filling liquid in the element.
(Floating ball) The liquid level transmitter is composed of a measuring diaphragm and the electrodes on the insulating plates on both sides respectively forming a capacitor. When the pressures on both sides are inconsistent, the measurement diaphragm will be displaced. The displacement is proportional to the pressure difference, so the capacitance on both sides is not equal. Through the oscillation and demodulation link, it is converted into a signal proportional to the pressure. The working principle of pressure transmitter and absolute pressure transmitter is the same as that of differential pressure transmitter. The difference is that the pressure in the low-pressure chamber is atmospheric pressure or vacuum.
The A/D converter converts the current of the demodulator into a digital signal, whose 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 measurement range, engineering unit conversion, damping, square extraction, sensor fine-tuning and other operations, as well as diagnosis and digital communication.
This microprocessor has 16-byte program RAM and three 16-bit counters, one of which performs A/D conversion.
The D/A converter fine-tunes the data from the calibrated digital signal from the microprocessor. These data can be modified by the transmitter software. The data is stored in the EEPROM, which is kept intact, even if the power is off.
The digital communication line provides a connection interface for the transmitter with an external device (such as a 205 intelligent communicator or a control system using HART protocol). This circuit detects the digital signal superimposed on the 4-20mA signal and transmits the required information through the loop. The type of communication is frequency shift keying FSK technology and is based on the BeII202 standard.