Why is it strictly prohibited to connect a digital display directly to the input terminal?
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Terminals 3 and 11 are used to connect 4-20mA two-wire instruments, and terminal 11 indicates that it is strictly prohibited to connect it directly to the input terminal; I don’t understand this… I want to connect a two-wire level gauge – how should I do that? Help! ! (The digital display is from Donghui)
This post was last edited by 1111111 on 2018-11-1 12:19. Donghui can be called a dog. The excuses given, the wiring diagrams drawn – ugh, it’s disgusting. On the terminal diagram, the reference terminal of the 24VDC power supply cannot be seen. I guess terminal 8 is the common reference ground. . . Use a multimeter to measure it. . . To prevent Donghui from acting recklessly, physical protection was put in place. :Lol, if terminal 8 is the common reference ground, then you need to short-circuit terminal 4 and terminal 8 in order to create a current loop, so that the meter can display the readings properly.
I connected the instruments directly to terminals 3 and 11, and everything shows normal... The manual doesn’t mention any consequences of connecting to the input terminals directly either...
"The meters are connected directly to terminals 3 and 11, and both show normal readings. If the readings are normal, use the white color; ignore everything else! . . If you’re curious, you can use a multimeter to check terminals 4 and 8 to see if they are connected; once that’s done, other things will become clear as well. :lol
On this display unit, terminals 4 and 8 are internally shorted; otherwise, normal display is not possible. After the internal shorting occurs, it is necessary to use the 24VDC power supply provided by the display unit to power the transmitter, and an external 24V power supply cannot be used. If the transmitter is connected to two power supplies by mistake, it will damage the meter. . .
The so-called rigorous direct connection is intended to prevent short circuits, which is why a label was attached. It means telling you that you can add a resistor to increase the matching impedance, prevent short circuits, and enable communication.