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Old November 25th, 2021, 06:09 AM   #1
Mas01
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Mitsubishi Q series... thermocouple disconnect detection

This question is about a Q68TD-G-H01.
When I disconnect the thermocouple connected to channel 8 of the module, I am expecting D111.F to go TRUE (i.e. a blue box should appear over the register D111.F), but this doesn't happen. When disconnected, the temperature value goes to a negative value but the disconnect is not detected.
I think I have enabled thermocouple disconnect detection (G0) by setting it to zero.

Can anyone understand why this isn't working for D111.F? It does work for D111.8 to D111.E.
Thanks
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Last edited by Mas01; November 25th, 2021 at 06:16 AM.
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Old November 25th, 2021, 09:59 AM   #2
PLCDontUQuitOnMe
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Are you sure that you are actually setting the conversion disable/enable word to 0? I'm just wondering why you have multiple bits all referenced as R0S3?



Have you tried directly addressing the operating condition setting request bit? The manual shows it is addressed to Y9, of course the actual address will be Y9 + head IO start value.



I am wondering if G0.7 is actually set to 1 and your instruction to move 0 into G0 is not working correctly.



If you go to device memory monitor, under buffer memory, you can input the head address of the card and directly read it's memory to check the status of the bit you are looking for.


The other thing I'm wondering if that checks out ok, is D111.E being overwritten somewhere else?



Also is the thermocouple in channel 8 giving the same values when moved to a different channel?


I would check the device memory monitor first and go from there.
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Old November 25th, 2021, 10:16 AM   #3
Mas01
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Thanks but I'm lost.
Where can I find "Device Memory Monitor" from the menu?
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Old November 25th, 2021, 10:20 AM   #4
PLCDontUQuitOnMe
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Select "Buffer memory batch" then put in the head address of the thermocouple card and start viewing its memory contents. Look for the enable/disable bit you are curious about for channel 8.
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Old November 25th, 2021, 10:25 AM   #5
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Thanks again....I will try that.
Just for info , I disconnected ch8 and I get -697. But when I disconnected ch7 I get zero.
Does this point to a particular problem?
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Old November 25th, 2021, 10:28 AM   #6
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Quote:
Originally Posted by Mas01 View Post
Thanks again....I will try that.
Just for info , I disconnected ch8 and I get -697. But when I disconnected ch7 I get zero.
Does this point to a particular problem?

When you disconnect other channels do they all go to zero as well?


I am wondering if it needs a value of 0 to trigger the "disconnected" flag. Do you have to tell the card what type of thermocouple is connected to every channel for it to calibrate the channel so that it is 0 when disconnected?



Someone with more knowledge of thermocouples might be able to answer this question.
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Old November 25th, 2021, 10:37 AM   #7
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Quote:
Originally Posted by PLCDontUQuitOnMe View Post
When you disconnect other channels do they all go to zero as well?


I am wondering if it needs a value of 0 to trigger the "disconnected" flag. Do you have to tell the card what type of thermocouple is connected to every channel for it to calibrate the channel so that it is 0 when disconnected?



Someone with more knowledge of thermocouples might be able to answer this question.
On the Switch Settings page, all channels are set to K-type thermocouples, which is what they are.
When I disconnect the other thermocouples, they all give zero. For some reason, ch8 gives me a big negative number when disconnected.
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Old November 25th, 2021, 10:47 AM   #8
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Quote:
Originally Posted by Mas01 View Post
On the Switch Settings page, all channels are set to K-type thermocouples, which is what they are.
When I disconnect the other thermocouples, they all give zero. For some reason, ch8 gives me a big negative number when disconnected.

Double check in the buffer memory that channel 8 is actually set for K type.



Do you have a spare card you can try to see if it is a problem with the card itself?
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Old November 25th, 2021, 10:49 AM   #9
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Quote:
Originally Posted by PLCDontUQuitOnMe View Post
Select "Buffer memory batch" then put in the head address of the thermocouple card and start viewing its memory contents. Look for the enable/disable bit you are curious about for channel 8.
Cheers PLCDUQOM, I did that and buffer 0 (g0) is set to all zeros as I expected...
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Old November 25th, 2021, 11:03 AM   #10
PLCDontUQuitOnMe
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Now if you scroll down to register 49, try disconnecting a few channels and see if you see the bits coming on for disconnect detection. Specifically channel 8
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Old November 25th, 2021, 12:31 PM   #11
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Quote:
Originally Posted by PLCDontUQuitOnMe View Post
Now if you scroll down to register 49, try disconnecting a few channels and see if you see the bits coming on for disconnect detection. Specifically channel 8
Cheers again.
I disconnected the TC connected to ch8...the disconnect bit for channel 8 is NOT being set (see the picture with 0000 0000 0000 0000). When I disconnect a couple of the other TCs, the appropriate bit is set.
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Last edited by Mas01; November 25th, 2021 at 12:52 PM.
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Old November 25th, 2021, 12:38 PM   #12
PLCDontUQuitOnMe
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Quote:
Originally Posted by Mas01 View Post
Cheers again.
I disconnected the TC connected to ch8...the disconnect bit for channel 8 is NOT being set (see the picturebwith 0000 0000 0000 0000). When I disconnect a couple of the other TCs, the appropriate bit is set.

Two ways I would go about this from here on out:


1. If possible and you have a spare, replace the card and see what happens
2. Download the manual for the card, go to the appendix where it shows all of the buffer memory addresses and their functions. Look through this and look at any channel specific areas of memory, and look to see if there is a setting difference between channel 8 and any of the other channels. I think this should only take like 20 minutes or so.
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Old November 25th, 2021, 12:40 PM   #13
Mas01
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Quote:
Originally Posted by PLCDontUQuitOnMe View Post
Two ways I would go about this from here on out:


1. If possible and you have a spare, replace the card and see what happens
2. Download the manual for the card, go to the appendix where it shows all of the buffer memory addresses and their functions. Look through this and look at any channel specific areas of memory, and look to see if there is a setting difference between channel 8 and any of the other channels. I think this should only take like 20 minutes or so.
Cheers for this. I've got the manual now, so I'll have a read. Thanks
Edit.... pictures now attached to my previous post

Last edited by Mas01; November 25th, 2021 at 12:52 PM.
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