Newbie seeking help: How to use a multimeter to check the condition of a two-wire instrument
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I’m a beginner asking for advice: the humidity sensor on one of the air ducts shows a reading of zero. It’s connected using a two-wire system, and I want to use a multimeter to check it, but I don’t know how to do it. . . When using a multimeter to measure the signal of a two-wire instrument, can one simply use the 4-20mA current range to make measurements at the terminal connections? The four-wire system is easy to understand: there are two power wires and two signal wires, allowing for the measurement of voltage as well as 4-20mA DC signals. However, in the two-wire system, there are only two wires in total – one for power and one for the signal – and I’m not sure if measurements are carried out in the same way First, thank you all.
Using the same testing method, the two-wire meter circuit requires a power supply.
It’s not clear whether the driving voltage of the multimeter is sufficient; it’s best to use a loop signal tester
A reading of zero indicates no output current; use a multimeter to check whether there is voltage at the terminals. If the voltage is 24V or higher, it means there is an open circuit inside the humidity sensor. If the voltage is 0, check the power supply and verify whether there are any open circuits in the current output circuit that prevent the 4-20 MA current from forming a complete circuit.
I don’t know either whether your probe is a thermocouple, a thermal resistor, or something else; it’s impossible to tell
Using a multimeter to check whether an instrument is good or not isn’t reliable in the first place!
If there’s voltage but no current, it’s broken; buy a new one, hahaha