Grounding issue with FP-TC-K on FP-TB-10

[Gerry S]

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

[Wayne.C]

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. 

[Gerry S]

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. 

[DirkW]

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

[Wayne.C]

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?

[Gerry S]

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. 

[Wayne.C]

Gerry,

Have you tried just one thermocouple with one FP-TC-K installed on the FP-TB-10? 

[Gerry S]

DirkW, I could try the module from my good system, but the good system is running and I'm also afraid of screwing it up somehow.  I've been trying to figure out a good way to test the new system components to see if they work without screwing up my good working system.  I can add each component one at a time to the good system and test each module one at a time right on the end of the good system.  That's a good idea.  I will try connecting the poorly working FP-TB-10 to my good system and see if it works better there.   Maybe the laptop has something to do with the problem.  I'm trying to hook up the laptop to the good system and see if everything reads correctly, but I don't want to have to reset the IP addresses of the good system modules.  Oh, I can reset the IP address of the laptop to match the good system and the subnet mask to match the good system.  Then the laptop will work I think. 

[Gerry S]

Yes, Centerbolt.  I have tried just one thermocouple plugged into the lone FP-TC-K that was on the FP-TB-10.  I have several digital output (LED modules that can plug into the TB-10) modules and the LED's go on and off as desired in MAX. 

[GenU1Chevy]

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.