Pressure Sensor Correct Wiring

The connection method of the pressure sensor generally include two-wire system, three-wire system, four-wire system, and some sensors have a five-wire system.

The two-wire pressure sensor is relatively simple, and customers generally know how to wire. Connect a line is to the positive pole of the power supply, and the other line that is the signal line connected to the negative pole of the power supply through the instrument. This is the simplest. The three-wire pressure sensor add a wire to the two-wire system. This wire directly connect the negative pole of the power supply, which is more troublesome than the two-wire system. The four-wire pressure sensor has two power inputs and the other two are signal outputs. Most of the four-wire system is voltage output instead of 4-20mA output. The 4-20mA machine called pressure transmitter, and most of them are two-wire system. Some of the signal output of the pressure sensor without amplification. The full-range output is only a few tens of millivolts, and some pressure sensors have an internal amplification circuit, whose full-range output is 0-2V. As for how to connect to the display meter, it depends on how large the meter's range is. If there is a gear position that matches the output signal, we can use it to measure directly. Otherwise, we should add a signal adjustment circuit. The difference between the five-wire pressure sensor and the four-wire system is small, and there are fewer sensors on the market with five-wire systems.

• Two-wire wiring

We generally use two-wire wiring. The two-wire system that is, the power supply and the load are connected in series. There is a common point, and the signal connection and power supply between the on-site pressure sensor and the instrument in the control room only use two wires, which are both the power line and the signal. The two-wire pressure sensor provides a static working current for the transmitter because the current at the starting point of the signal is 4mA.DC. At the same time, the electrical zero of the instrument is 4mA.DC, which does not coincide with the mechanical zero. This live zero is useful for identifying the fault such as power outage and disconnection. Moreover, the two-wire system also facilitates the use of safety barriers, which is conducive to safety and explosion protection.

• Three-wire wiring

In order to reduce the volume and weight of the pressure sensor, improve the anti-jamming performance and reduce the wiring, some instrument manufacturers changed the power supply of the pressure sensor from 220V.AC to low-voltage DC. If the power supply is taken from the 24V.DC power box, the low-voltage power supply creates conditions for the negative line sharing, so there is a three-wire sensor product. The so-called three-wire system uses a line at the positive end of the power supply, and a line at the positive end of the signal output. The negative end of the power supply and the negative end of the signal share a single line. The power supply is mostly 24V.DC, the output signal is 4-20mA.DC, the load resistance is 250Ω or 0-10mA.DC, and the input resistance is 0-1.5KΩ. Some of them have mA and mV signals, but the values of their load resistors or input resistors depending on the form of the output circuit.

• Others

Due to the different working principles and structures of various sensors, different products have emerged, which determines the wiring methods of the two-wire, three-wire, and four-wire pressure sensors. A small number of frequency converters on the market don’t have a 24VDC power supply, and a small number of power supplies are 10VDC. For Some high-power pressure sensors, 10VDC power supply can’t drive it, then must connect external power supply 24VDC. In this way, the frequency converter has four terminals:
power supply +, power supply -, feedback + and feedback -. Current type four-wire connection: power +== power supply +; power supply -== power supply -; signal +== feedback +, signal -== feedback -. Current type two-wire connection: power supply +== power supply +; signal +== feedback +, power supply -== feedback -. Voltage type three-wire connection: power +== power supply +; power - (signal -) = = power supply - signal + = = feedback +, power - (signal -) = = feedback -.

The pressure sensor can directly connect with the frequency converter. By connecting the pressure sensor to the signal loop, you can use the 24V power supply on the frequency converter.
The correct wiring method is useful for measuring the pressure of the measure medium accurately. The wiring of the pressure sensor depends mainly on the set measurement method and the range module. In general, pressure sensors often use shielded twisted pair cables to connect analog signal cables, which not only reduces the interference in the noisy environment of the construction site, but also reduces the error caused by the measure medium. In order to prevent the potential difference between the two ends of the analog quantity from producing interference analog signal, one end of the analog quantity must be grounded to avoid this situation.