How does a two-wire 4-20mA pressure transmitter both supply power and transmit signals?

Structurally, a two-wire 4-20mA pressure transmitter consists of three main components: the sensor, the conditioning circuit, and the two-wire V/I converter. The sensor converts physical quantities like temperature and pressure into electrical parameters. The conditioning circuit amplifies, adjusts, and converts the weak or nonlinear electrical signal from the sensor into a linear voltage output. The two-wire V/I conversion circuit controls the overall power consumption current based on the output from the signal conditioning circuit. Simultaneously, it obtains and stabilizes voltage from the loop to power both the conditioning circuit and the sensor.

The principle of a two-wire pressure transmitter relies on utilizing the 4-20mA signal to supply its own power. If the transmitter's self-consumption exceeds 4mA, it cannot output the lower limit of 4mA. Therefore, two-wire transmitters are typically designed to ensure their total circuit power consumption (including the sensor) does not exceed 3.5mA. This is one of the fundamental design principles for two-wire pressure transmitters and two-wire temperature transmitters.

Working Principle of Two-Wire 4-20mA Pressure Transmitters: The internal conditioning circuit and V/I converter within the sensor transform physical quantities (such as pressure or temperature) into a 4-20mA current signal. This signal serves as the power source to drive the sensor's operation while simultaneously converting to a voltage signal via a load resistor for external device readout. For example, when outputting 4mA, part of the current powers the sensor, with the remainder transmitting the signal.

This design simplifies wiring, reduces costs, and is particularly suitable for long-distance transmission and explosion-proof environments. For instance, a pressure transmitter mounted on a gas storage tank requires only two wires connected to a PLC to accomplish both power supply and data transmission.

For details, please contact Qi Huang: qihuang@utopsensor.com