Currently am using a GRV-EPIC-PR1 with a GRV-IV-24 for some analog sensors for temperature and humidity. The sensors are hooked up to the same power supply. When I touch the sensor to increase the temperature, the values for all of the other sensors similarly increase, even without touching them. Is this because the GRV-IV-24 is not isolated channel-to-channel? And if so, is there a workaround to this?
Hi Forest. Welcome to the Opto22 forums.
It sounds like you have some earth currents floating around for sure.
The solution would be to use the GRV-IVI-12. Its the closest isolated version of the module you are using.
EDIT. Fixed the original ‘24’ channel module post for the actual 12 channel module post (Thanks @philip )
Thanks for the response. Is there no option to use the IV-24? Seems like getting the IVI-24 will have a long lead time. How does the module have 24 channels to use, but they aren’t able to be used in conjunction with one another?
Its not that they cant be used in conjunction with each other (of course they can), its just that with your current wiring, there is a ground current circulating somewhere and so just like a rising tide lifts all boats in the harbor, a common ground current raises all voltages on the module.
Lets take a look at the wiring diagram for each module…
Starting with the GRV-IV-24
Notice how all the first bank of 12 inputs share the same ground.
Same with the second bank of 12 inputs.
Also notice how the two banks are isolated from each other… we will get back to that in a sec…
Now lets look at the GRV-IVI-24
Notice how each input has nothing at all in common with any other input.
This module is fully isolated.
No matter what one input ground reference is, it can in no way impact any other input.
This is not a bad summery of the situation.
So a few tips.
If you are dealing with mv inputs, things are going to be more sensitive.
The power supply should be tested / inspected.
The temperature sensors used should be understood, if they are metal tipped, are the tips grounded, can they be safely grounded?
Is there more than one ground point in the setup?
If the sensors are different types and only one type is metal, then move it to the second bank on the module so it does not impact the other sensors.
Hope that helps you get up and running.
There is no GRV-IVI-24 module that I know of - there is a GRV-IVI-12 which is only 12 channels, so you would need to use two of them to replace a full GRV-IV-24
Pay attention to this, as I suspect this is where your issue is.
DOH! Thanks Philip… Apparently do I not only have no clue about our products, but I also cant read on top of not being able to type!
12 channel isolation takes up a lot more space in the module, so there is no room for a full 24 channels of isolated inputs in the same space.
A shield wire grounded on both ends ( the instrument and in the cabinet) can cause issues depending on how the instrument is ground referenced. For me, I found grounding shield wires in the cabinet is the cleanest. I have had ground loop issues in the past with grounded Type K thermocouples. They are vary difficult to isolate.
If you can disconnect all but two channels (through a fuse disconnect) it may help to simplify the problem.
Since it is an IV module, I would suspect there is a temperature transmitter involved, so checking things on the transmitters signal and power supply side is where I would look first.
