Current analog module

Hi

Im really confused. I have a 4-ch analog OUT module (Mitsubishi FX2N-4DA), i have used the three (3) channels. Just this evening, I did connect to the 4th channel a 4-20mA controlled air regulator..and my problem has started.

Connected on my 1st channel was a VFD (0-10Vdc), 2nd channel was a temperature controller (4-20mA) and 3rd channel was a VFD (0-10Vdc). If I connect my air regulator analog signal on my FX2N-4DA module, I get an error on my temperature controller (OMRON, E5En-H) which reads E333 (referred to the manual, it is A/D converter error which is probably cause by noise).

I disconnect my air regulator and the error was OUT. I connect my air regulator and the error is IN.

I disconnect the temperature controller & connected the air regulator still on 4th channel. I am controlling fairly well. Connecting temperature controller on 2nd channel, then the error is IN AGAIN.

I exchange my channel 3 & 4, but still conflict between two 4-20mA signals are still observed.]

What would be the possible error?
Pls. help me

Without seeing the wiring, it could just be a ground-loop problem with the current outputs. Can you stuff an isolator between the second current loop output and the air regulator as a test?

rdrast said:

Without seeing the wiring, it could just be a ground-loop problem with the current outputs. Can you stuff an isolator between the second current loop output and the air regulator as a test?

Click to expand...

Hmmm, this may sound naive but how can I do the isolation on my 2 current OUT?

There are many different vendors, I don't know what is commonly available by you, but I'm referring to something like one of these.

They simply take an input, isolate it completely from any other connections, and re-transmit it (again, on a completely isolated output). If there are any grounding problems (which can occur easily in current loop circuits), isolators will eliminate them.

rdrast said:

There are many different vendors, I don't know what is commonly available by you, but I'm referring to something like one of these.

They simply take an input, isolate it completely from any other connections, and re-transmit it (again, on a completely isolated output). If there are any grounding problems (which can occur easily in current loop circuits), isolators will eliminate them.

Click to expand...

Is there any other repair option for this other than buying an isolator? buying isolator would take days, I could not wait, we need to test asap.

Could it be possibly because of improper grounding? I have a leak of about 2V..

I think I have a problem with my noise filter. But I'm still not sure. I connect L1 to my noise filter, removed L2..read L1-ground 110 V (okay), read L2-ground 110V(???)

How would I check if this filter is not doing what it supposed to do?
Please help..

I concur with RDrast, the problem is classic ground loop common mode, although it is more commonly seen with multiple single ended inputs than it is with AO's.



Notice that
a) each negative side of the AO is also a common ground for all channels. These are single ended analog outputs.

b) note #2 in the manual says, "Apply one point grounding"

The cumulative common mode ground potential difference between points saturates the input of the Omron, driving it full scale in one direction or the other, depending on the polarity of the common mode voltage.

It is unlikely that it is noise, even though Omron error message defines it so.

You need at least one isolator. There's a fair shot that swapping the Omron for a model with an isolated input might get around the issue, too.

Should i isolate too my signal grounding with my power line ground?

Note that the earth ground is a separate ground symbol from the AG (analog) ground symbol. The shields for the wiring attach to the earth ground.

I would not connect any signal ground to the earth ground. But the problem is that internally, any of the instruments you are connecting to might have their signal grounds and earth grounds connected, which is creating a ground loop problem.

Since you can't change the internal wiring of the devices, ground loops are resolved by isolators.