4-20 ma cable choice

Hi guys,

Can I have a last wee bit of help with choosing cable for a 4-20ma sensor?

I am going for a Flexible twisted shielded (foil or braid haven't decided yet) but what I am not sure about is the impedance. Have some cable that looks great but it has a nominal impedance of 110 ohms. Do you think this would be ok. It is typically used in a lighting data application but it is flexible and shielded. My other choice is a cable used for the audio industry. Again, it's flexible twisted and sheilded...

Many thanks in advance

Is that 110 ohms for both to and from the sensor ?
Anyway, 110 ohm or 220 ohm is probably both OK.
The sensor spec sheet should tell you max cable resistance. Typical is something in the region of 500 ohms @ 24V.

If you're referring to the characteristic impedance of the cable, it's completely irrelevant to 4-20mA applications, unless you have some signals with astonishingly high frequency.

This year we used over 7000 mts of LIYCY 2x0,5 cable for 4-20mA analog signals with NO problem

Confirming AutomaticLeigh's response:

4-20mA is normally considered DC, hence characteristic impendance has no practical meaning.

Impedance rating becomes an issue with

1) some transducers that are excited with pulses or AC, but not on the 4-20mA conditioned signal end.

2) digital data communications

nonuke said:

This year we used over 7000 mts of LIYCY 2x0,5 cable for 4-20mA analog signals with NO problem

Click to expand...

That seems very sound to me. I would add not to use cable with too small a section, because of the possible voltage drop, which can result in inability to drive up to 20mA. But if the cable isn't too long, anything from 0.1mm² up would do, at least it always did it for me. For short distances (up to 30m) I used to use ribbon cable for 4-20mA signals. Of course, there's absolutely no need to use anything over 1mm² "just to stay on the safe side".

Kind regards,

If you want to see quick changes like > 10Hz use good shielded cable.
If signal is high freq then use other system with diff signals and feedback