Thermocouple 1746-NT8

[cornbread]

Trying to understand how the range error bits work on a 1746-NT8. I have the TC simulator hooked to I:4.0. When I take the reading negative the open circuit error bit opens. Note the input read the TC temperatire just fine. Probably doing something real stupid...but it has been one of those days. Any help would be greatly appreciated.

 

[Ken Moore]

The snapshot you posted does not show an open circuit error (bit 12). You show bits 0, 5, 7, & 15 as true, per the manual this means:
Bit 0: Channel enabled
Bit 5: Engineering units x 10
Bit 7: Max on open circuit
Bit 15: Channel error

 

[cornbread]

Bit 12 does not go open until I drive the temp below zero.

 

[Ken Moore]

Can you post your .rss file? Might be something in your module configuration. What type of thermocouple are you using? Your status word shows all zero's which is the default for Type J. I thought Type J's were good for 0-750C, so of course you will get an error below zero, since J's aren't supposed to go that low.

 

[cornbread]

According to the Rockwell user manual type J thermocouples range from -210 deg C to 760 degree C. I'm able to read down to -210, but as stated the open error bit is toggle at zero and below.

I'll try to get the .rss file later today.

 

[cornbread]

I think I got it. Did not realize that you have to tell the module you want the status word (bit 15). Since my program only configured the module for an Data word, I have never looked at the "status". I'll put together some code and make sure it works and post the results here.