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I have a pressure sensor with 24 V, GND and 4-20 mA signal output pins. It will communicate with a PLC. I will only use 3m of wire max. for each pin. The installation will be on the rooftop maybe a few meters away from a VFD, but 3-5% noise in the signal is totally acceptable.

Should I twist the signal and the GND wires? If yes, isn't it a problem that the current flowing in the GND wire won't be equal to the current flowing in the signal wire?

Datasheet: https://www.belimo.com/mam/general-documents/datasheets/en-gb/belimo_22ADP-184.._datasheet_en-gb.pdf

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  • \$\begingroup\$ Is it a 2-wire sensor (loop powered, with shielded cable) or 3-wire (with shield as 0 V / ground connection and require to power the sensor)? \$\endgroup\$
    – Transistor
    Commented Jan 8 at 23:07
  • \$\begingroup\$ It has 3 wires. 24V supply, GND, 4-20mA output. \$\endgroup\$
    – Gurul_01
    Commented Jan 8 at 23:14
  • \$\begingroup\$ you also should have lightning protection \$\endgroup\$
    – jsotola
    Commented Jan 8 at 23:14
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    \$\begingroup\$ Please edit your question to include a datasheet link. You already stated that it has a ground connection but we're not sure that it's actually used by the sensor or just grounds the case. \$\endgroup\$
    – Transistor
    Commented Jan 8 at 23:17
  • \$\begingroup\$ I have added the datasheet. \$\endgroup\$
    – Gurul_01
    Commented Jan 9 at 10:42

2 Answers 2

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By twisting the wire you will reduce the area of the wire and make it less susceptible to magnetic noise. It is usually a good idea for most sensors and power systems especially any that need have increased magnetic noise immunity. If you want to reduce electric field susceptibility then shield the wire.

The GND wire will carry the return currents from the signal and the 24V power and the ground of the sensor will be referenced from this ground. If the power changes you could get common mode noise. It's unlikely that this is an issue because it's a 3-wire device.

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It's a pressure sensor assuming that you are not using it as an ultrasonic microphone it will be producing a slowly changing signal.

It's a controlled current source induced voltage will not show in current measurements.

Twisting or not twisting will have little effect on performance.

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  • \$\begingroup\$ Magnetically induced current would show in current measurements. OP should minimise loop area. \$\endgroup\$
    – Simon Fitch
    Commented Jan 9 at 16:39
  • \$\begingroup\$ yeah but that would take several volts of induced EMF \$\endgroup\$
    – Jasen Слава Україні
    Commented Jan 9 at 20:43

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