Liquid level transmitter wiring method
A pressure transmitter is a device that converts the pressure of a gas or liquid into a usable electrical signal. Pressure transmitters can be divided into two-wire system, three-wire system and four-wire system according to the wiring method. What you see should be a four-wire pressure transmitter. Two power lines, two signal lines. The power supply is connected to 24v DC. The simple detection method is to use an ammeter or voltmeter to connect both ends of the signal line. After the power supply is connected, the ammeter will have 4ma current or the voltmeter will have 0v or 1V voltage. The current transmitter generally has 4 terminals, two of which are wired, and the other two do not need to be wired. The DC24V power line of the transmitter is also a 4-20mA signal feedback line, that is to say, your secondary The AI point of the meter or DAS (Data Acquisition System) should have a DC24V output.
Liquid level transmitter, the general output signal is current 4-20MA, 0-20MA, or voltage 0-5V, 1-5V, 0-10V, etc., usually the current type is two-wire or four-wire system, and the voltage is three-wire system output. At present, many of them do not have a 24VDC power supply, most of them are 10V, and some transmitters with high power consumption cannot be driven by a 10VDC power supply, so they can only be connected to an external power supply of 24VDC. In this way, there are four terminals on the liquid level: power supply +, power supply -, feedback + and feedback -.
The four-wire wiring method of liquid level transmitter wiring: power supply +==power supply +; power supply -==power supply-; signal +==feedback+, signal -==feedback. The current-type two-wire connection method of the liquid level sensor wiring: power supply +== power supply +; signal +==feedback +, power supply -==feedback-, if not remote transmission, only need to connect 24V voltage +, -, if you need remote It is necessary to form a circuit, for example, 24V+ is connected to the pressure gauge+, the pressure gauge- is connected to 4~20mA+, and 4~20mA- is connected to 24V-. There may be terminals in the middle, so please refer to the circuit diagram.
The voltage type three-wire wiring method of liquid level sensor wiring: power supply +== power supply +; power supply – (signal -) == power supply -; signal + == feedback +, power supply – (signal -).
How liquid level transmitters work
The working principle of the liquid level transmitter is that when the two 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 delta element (that is, the sensitive element), and pass through the isolation diaphragm and the filling in the element. The liquid is sent to both sides of the measuring diaphragm.
The (float) liquid level transmitter is a capacitor composed of a measuring diaphragm and electrodes on both sides of the insulating sheet. When the pressure on both sides is inconsistent, the measuring diaphragm will be displaced, and the displacement is proportional to the pressure difference, so the capacitance on both sides is unequal. 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 of the low pressure chamber 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. A microprocessor controls the operation of the transmitter. Additionally, it performs sensor linearization. Reset the measuring range. Engineering unit conversion, damping, square root, sensor fine-tuning and other operations, as well as diagnosis and digital communication.
There is 16-byte 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 data from the microprocessor and the corrected digital signal, which can be modified by the transmitter software. The data is stored in EEPROM, even if the power is cut off, it will be kept intact.
The digital communication line provides an interface for the transmitter to connect with external devices (such as the 205 intelligent communicator or the control system using the HART protocol). This circuit detects the digital signal superimposed on the 4-20mA signal and sends the required information through the loop. The type of communication is frequency shift keying FSK technology and according to BeII202 standard.
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