0/4-20 mA signal running long distance.

Hi,

We are making proposal for centralized monitoring & logging device for our biggest client. The purpose of this system is to monitor temperature/ RH reading (via analog signal of 0/4-20 mA) & log it to a database being retrievable anytime.

The manufacturer of the "remote AI module" specifies that it should be located no more than 50m from the temperature/ RH controller. I would like to countercheck their claim on this, because I've read many threads on the forum that current loop runs long way without signal problem. So, I called them up & ask for the max. impedance of the "remote AI module" but they said it was not specified.

The wire they recommend is AWG16 (1.25mm2), shielded.

Is there any other way to countercheck the maximum length the "remote AI module" should be located? Anyway, the AI module is 220 Vac rated.

Thanks

It may be that the module will work at much greater distances but, if the manufacturer states that the max. distance is 50 m then they will most like not guarantee the module if you decide to install it further away. If you decide to install the unit 100m away and it fails after a few weeks what do you do ?

Dua Anjing said:

If you decide to install the unit 100m away and it fails after a few weeks what do you do ?

Click to expand...

But is it even believable that a current loop is limited only to 50m? I've read on this forum many current loop running a mile without problem (as they claim)..I'm thinking maybe the manufacturer was being way too safe or maybe they wanted us to buy many modules marketing strategy?

As i said it may well be that the 20 mA signal is good for a lot further than 50m but if that is all that the manufacturer says it is good for then you can't complain if you install it further apart and it doesn't work or isn't accurate. I think that the manufacturer may be being "way to safe" but if you need greater distances then I suggest you find a manufacturer that has a product they will guarantee at those distances.

You quote several bits of info

theripley said:

Hi,

monitor temperature/ RH reading (via analog signal of 0/4-20 mA)

"remote AI module" specifies, no more than 50m from the temperature/ RH controller.

wire they recommend is AWG16 (1.25mm2), shielded.

the AI module is 220 Vac rated.

Click to expand...

Without component catalog number I am left wondering if its possible that you could have misread the specs

As 50 m might be from the temperature probe to the RTD to the 0/4-20 mA controller which might be powered by 220 volts.

If you could supply those part number we can easily guide you with your selection

Please see attached page for your reference. If I still lack information, please don't hesitate to ask.

The problem with 4-20 mA signal distance isn't impedence, it's EMI/RFI. If you have good shielding, good grounding, and aren't running past a lot of big motors, flourescent ballasts, etc. you should be fine. I've run 4-20 mA much further than that without problems. The manufacturer is pulling a CYA (Cover Your A..), which they have every right to do. They can't be expected to write a blank check to every system designer, many of whom aren't as qualified as they should be.

If you are willing to assume responsibility then go ahead - watch your wiring, use separate conduit, make connections in terminal junction boxes, tie shield ground at one end only to a good ground, and you should be just fine.

Sounds good to me. I guess it will be my risk. I'll post updates in the future. Thanks!

aha it is yamatake(honeywell)
your line is indeed 4/20 mA
but it is digital communication and as the line gets longer the speed is dropped. a normal analog signal is steady and will be oke for miles but digital is another story.

I work a lot on reeferships with same type of instruments.
are the temp and humidity already in place or new?
if new i would suggest to have long cables on your Pt100 sensors and make humidity old fashioned with a small water sock on a Pt100 sensor.
all cables to central point or points and then use a metering device.
you will not need any MCS as they are expensive and not needed in your case.
you may send me an email for details.

greetings paul,