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Old June 30th, 2020, 12:57 PM   #1
phuz
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Scaling changes with 1794-IT8 over Ethernet to L81

Just commissioned two new skids for a customer. Each has a 1794 chassis over Ethernet back to an L81. The second module of each chassis is a 1794-IT8 and each has 3 Type J thermocouples. The temperatures we are measuring are around 30C, so the raw input from the module normally shows 300. What has happened now is that these readings will increase by a factor of 10 to ~3000. This occurs on all three thermocouples on both 1794-IT6 modules. The TCs are Type J and the module is set for Type J. Not much configuration in these, so what could possibly cause the resolution to increase that much? CJCs are installed. TB3T bases are used.
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Old June 30th, 2020, 01:27 PM   #2
id10t_error
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What do you have selected for the data format?
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Old June 30th, 2020, 01:33 PM   #3
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Quote:
Originally Posted by id10t_error View Post
What do you have selected for the data format?
set to C
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Old June 30th, 2020, 01:38 PM   #4
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I just noticed that each module does have a CJC fault, but they appear to be connected per the manual.
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Old July 1st, 2020, 05:36 PM   #5
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Update:
When using grounded TCs, terminal #16 needs to be tied to ground.
Our issue has been resolved.
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Old July 1st, 2020, 07:31 PM   #6
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Quote:
Originally Posted by phuz View Post
Update:
When using grounded TCs, terminal #16 needs to be tied to ground.
Our issue has been resolved.

What terminal base are you using?

Isn't #16 the 24v dc common to power the base and module power.

Can you point to this tidbit of info.

Don't like grounded TC's. Ground loops and noise problems. see pdf

https://blog.wika.us/products/temper...vs-ungrounded/
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Last edited by Mickey; July 1st, 2020 at 07:34 PM.
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Old July 1st, 2020, 10:02 PM   #7
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TB3T base.
I think it is, but apparently this was a Rockwell secret for grounded TCs.
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Old July 2nd, 2020, 12:29 AM   #8
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Quote:
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TB3T base.
I think it is, but apparently this was a Rockwell secret for grounded TCs.

HMMM? Whatever works.
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Old July 2nd, 2020, 06:25 AM   #9
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HMMM? Whatever works.
Exactly! I saw no reference to this in the manual, but this came from a second call to Rockwell and apparently is one of their undocumented notes.
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