11-22-2008 04:12 PM
HI. I use FieldPoint with Labview to run diesel engine exhaust simulation reactors for the purpose of developing catalytic converters. I am putting together a new system but have encountered a problem with a grounding issue on a FP-TC-K thermocouple input module. I have the FP-TC-K on a FP-TB-10 module. It reads temperatures perfectly fine as long as nothing touches the thermocouple. As soon as I touch the thermocouple with my hand (or a wire connected to ground) the readings jump around. Over 5 seconds it may read: 26.7, 29.5, 22.4, 30.8, 26.1, 33.9, 27.2, 29.2, 30.1, 25.8, 33.6....etc. But when I'm not touching the thermocouple it is easily steady to only two tenths of a degree: 26.14, 26.19, 26.33, 26.23, 26.09, 26.12...etc. OK, so it appears there is a grounding issue somewhere. I tried using both a FP-I601 network module and a FP-2001 network module. Neither solved the problem. I have many of each module: FP-TC-K's and FP-TB-10's. I tried to use many combinations of them, but they all give me the same problem. I connected a FP-TC-120 module and I don't have the problem with that module. It reads the temperature steadily whether or not I am touched the thermocouple. I removed all other modules from the network module, the problem was still there. I am running on a Dell laptop computer using a crossover ethernet cable. The laptop is plugged in. I tried unplugging the laptop from the 120V power and running on battery power, it didn't help. I have an almost identical system running on a Dell duoprocessor desktop about 10 feet away and it runs awesome. Any ideas .....PLEASE...pulling hair out...will be bald soon....
Thanks,
Gerry
11-24-2008 08:00 AM
Gerry,
This sounds like a noise/ground loop issue. The FP-TC-120 module has differential inputs. The FP-TC-K module can either be used as 2 single ended inputs or 1 differential input. Make sure you are using the differential configuration.
11-24-2008 09:50 AM
Thank you, centerbolt. I am using omega type K thermocouples. I have looked and looked but can't find any way to switch between single-ended and differential configurations on the FP-TC-K. How do I switch to differential configuration for the FP-TC-K? I thought it was just a matter of plugging in a normal minithermocouple connector.
11-24-2008 11:14 AM
It is. There is no differential/single ended configuration difference.
Could you try the TC-K module from your system that works fine to male sure it isn't the module that is demaged somehow?
DirkW
11-24-2008 12:24 PM
Gerry,
It's a bit confusing. The data sheet for the FP-TC-K indicates that it can be used single ended or differential. The manual for the FP-TB-10 says nothing about the actual internal circuitry. Have you tried a single thermocouple per module and leaving the second input unused?
11-24-2008 02:48 PM
centerbolt, I have tried several times using only one thermocouple per channel. I think it's a grounding issue of some sort because if I connect a wire from the thermocouple to the metal water pipe at the sink the erratic behavior begins again. Jeepers, I would say for sure it was the thermocouple is shorted or something but I've tried many different thermocouples.
11-24-2008 02:55 PM
Gerry,
Have you tried just one thermocouple with one FP-TC-K installed on the FP-TB-10?
11-24-2008 02:55 PM
11-24-2008 03:01 PM
01-10-2011 10:03 AM
Hello all,
What was the final outcome on this problem? I am currently have the same problem with my machine and have found that grounding the system seems to work better but not totally. As soon as I touch one thermocouple on the same breadslice (FP-TC-K) the other thermocouple will go crazy. The temperature moves up and down ±6 °C. If someone could please let me know the cure for this problem I'd appreciate it. Thanks, Jeff K.