Adding Thermocouples

Hello, I'm need to add four tc to a steam dryer that had an existing tc in it. I'm using j type tc and I'm putting them through a ab-nt4 tc module that is in a slc 5/04. All I want to do is read the actual temp for now, but i am going to use it for full automation later. I'm using a panel view 600(touchscreen only) to read the temp. The problem I have is I can't get them to read correct temp. I should be in the 300 degree F, but I am reading around -800 degrees. I'm using an existing program to read the temps that has SCP (scale w/parameters) math instruction for the first rung and the second rung has a equal comparison as the input and move for my output. Has anybody seen this before?

Darren

Sound like a polarity problem. I would also check card configuration,
"C" or "F" and data format ( engineering units will give you
temperature, directly)




http://www.omega.com/techref/thermcolorcodes.html

Thanks For the tips. I tried reversing polarity and checked config of the channels and also I did a auto calibrate without any success. Any other help with this problem would be greatly appreciated.

Darren

Lost of things to watch for with thermocouple installation.
Cold junction installed, ungrounded thermocouple? grounded thermocouples? See this doc for install.
http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1746-in010_-en-p.pdf


Post your code (.rss file, just zip it and post ) if you can.

Darren,

You didn't say how much experience you have with these, so I'll share some of the things I've learned playing with thermocouples-

1. Red is always negative, and thermocouple wire connections must be extended with more thermocouple wire.

2. Check your module hardware and configuration by shorting the input terminals. It should read the local temperature.

3. I couldn't tell if the NT4 input commons are isolated from each other. If they're not, you need to use ungrounded thermocouples. I've had trouble with grounded thermocouples picking up noise on the machine (especially if VFD's are involved) and throwing your temperature way off. Remember that thermocouples are millivolt generators and a tiny ground imbalance can wreak havoc.

4. It's been a while since I've played with an NT4, but doesn't it return the actual temperature?

Joe T.

Yes, the NT4 returns the actual temperature - you shouldn't need to scale it if the module is set up correctly unless its set up to format for a PID. Depending on how you set up the module it will return the actual temperature in .1 degee units, that is 300 would be 30.0 degrees, or whole degree units.

Thanks for the info. everybody. The tc were wired in backwards. And just to answer the question about the nt4 module having isolated commons, they do.

Thanks again,
Darren Johnson