Issues with the power supply for the instruments
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Newbie seeking help: Why do some instruments indicate a 24V DC power supply, while others require a 4-20mA current supply? I’m confused
They are all powered by 24VDC, except that some are powered separately via signal dry contacts. Some have wet contacts for 4-20ma signal distribution
Please understand the \"2-wire\" and \"4-wire\" signal types!
Dry and wet refer to active and passive systems; passive devices require separate power supply. As mentioned above, systems like the \"two-wire\" and \"four-wire\" types are used, and pressure transmitters generally generate active signals, such as 24VDC + 4~20MA. There is also an AO current output, which is commonly used in control valves.
Given the variety of answers to your question, it’s you who’s confused us all:D.
“What does ‘4-20ma current supply’ mean? I don’t understand. 4–20mA is the signal current used for transmission, while the power supply provides the electricity.
Two-wire instruments, transmitting a 4–20mA current signal, powered by 24VDC. The signal and power share a pair of wires.
Two-wire instruments transmit signals of 4-20mA via just two wires. For four-wire instruments, the 4-20mA signal line requires two wires; in addition, a power line is needed for supply, with the supply voltage can be either 24V or 220V
It is determined by the principle of the instrument.
Hehe, I didn’t explain it clearly before… For two-wire instruments, such as transmitters, it’s the DCS card that provides 24V power. As you mentioned, for control valves, does the DCS card supply 24V voltage or 4-20mA current as the power source? Because I used a multimeter to check the terminals of the control valve earlier and found no voltage there; without voltage, how can power be supplied? That left me a bit confused
Dry, wet. Your answer is really weird.