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Some transducers have both voltage and current output options. I currently use voltage outputs with around 15m BNC cables single-ended. So they are open to interference as well. Sometimes during data logging I observe noise.

Would using current output/loop in this case reduce the interference picked up along the way from the transducer to the receiver/adc?

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  • \$\begingroup\$ Why kind of noise? amplitude, impedance, duration? \$\endgroup\$ – Tony Stewart EE75 Jan 17 '18 at 3:15
  • \$\begingroup\$ Why not try it? \$\endgroup\$ – vofa Jan 17 '18 at 3:18
  • \$\begingroup\$ Since it was my design, I often used 600 ohm differential line drivers like a SSM2142. It is good for DC to 50 KHZ, but not RF. I used a TL072 op-amp as a driver for it to add gain and offset. If your only sending RF, consider Ethernet transformers as isolation. Use a 10 base-T setup. \$\endgroup\$ – user105652 Jan 17 '18 at 4:18
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A current signal as opposed to a voltage signal isn't so much to reduce environmental noise pickup, but to eliminate errors caused by ground offsets and the series resistance of the cable. Current loop can be lower noise, depending on your noise sources, but there are also scenarios where a voltage signal can be lower noise.

There are other ways to transmit signals with little noise pickup, like balanced differential voltage in a shielded cable.

However, for the best noise immunity, send the information digitally. Put a micro as close to the source of the signal as possible. Have that sample it digitally, then send the information on.

With digital, you can guarantee correct reception as long as some minimum signal to noise ratio is met. You can also include a checksum, so that if data is corrupted, the receiver can know it is corrupted and deal with it accordingly. You can also send multiple signals over the same channel quite easily.

Unless you have very high bandwidth requirements, it is usually best to convert to digital as early in the process as possible, then do everything digitally from there on.

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I currently use voltage outputs with around 15m BNC cables single-ended.

The basic problem sounds like this (at the top): -

enter image description here

Using a balanced system can provide very decent benefits.

Would using current output/loop in this case reduce the interference picked up along the way from the transducer to the receiver/adc?

If you are still using an unbalanced system then you might not see benefits.

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  • \$\begingroup\$ But can current from current source effected from EMI? I thought the onoly way to change a current signal to inject current. \$\endgroup\$ – floppy380 Jan 17 '18 at 11:45
  • \$\begingroup\$ A current signal is affected differently to a voltage signal but both are equally affected when differential signalling is not used. \$\endgroup\$ – Andy aka Jan 17 '18 at 11:48
  • \$\begingroup\$ Thanks a lot. If I use balanced system as you mentioned and use twisted shielded pair what type do you recommend for 0 to 10V DC signals? For example at the moment I have this cable: alphawire.com/en/Products/Cable/Alpha-Essentials/… It says 8.0 Twists/foot (min). Would that be enough to mitigate EMI especially 50/60Hz magnetic coupling? I havent used twisted pair before and a balanced system \$\endgroup\$ – floppy380 Jan 17 '18 at 11:48
  • \$\begingroup\$ I can't get to the data sheet for alpha wire - it requires a login. 8 twists per foot is OK. The problem is that you know there is noise but you don't know or understand the source of the noise. Balanced signalling generally improves things by 10 to 20 dB but if the noise source produces common mode voltages on the cable that is beyond the capability of the balanced receiver then nothing will work. How much does it cost to try it out by buying some cable. Maybe you can borrow some cable? \$\endgroup\$ – Andy aka Jan 17 '18 at 11:54
  • \$\begingroup\$ I can buy cable, but I dont know the one I have is adequate. You wrote "8 twists per foot is OK." So I can live with this then? \$\endgroup\$ – floppy380 Jan 17 '18 at 13:12

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