adccommunitymod (AutomationDirect) asked a question.
thermo card jigders
Created Date: September 23,2014
Created By: a agnone
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What would cause erratic numeric readings on a F2-04THM card? J type thermo wire is connected. We changed out the card, removed all the wires and checked for shorts and opens. Grounded the common of the 24v power supply to neutral. I seen this before, but this time can not solve the problem. There are two cards on the rack and the other one is working fine!
Created Date: September 23,2014
Created by: Bob S BN
I have seen haphazard wiring done at annual TC replacement that would let one of the wires touch the junction housing causing erratic readings.
We also had one zone of one of our furnaces where the combination of heating elements and proximity to the TC would induce current on the TC wire proportional to the element power draw. Had to put a SS tube in that would fit the ceramic protection tube in an effort to shield the TC.
We also ground the - of all TCs at the card as well as the 24- to reduce fluctuations.
Hope this helps,
Created Date: September 23,2014
Created by: ControlsGuy
I was just having a very similar issue with a six-year old DL06 that had two F0-04THMs. My problem seemed able to strike anywhere, it wasn't consistently with one card.
We looked at the cabling, swapped the cards (since at that point it did appear confined to one card), swapped the wiring arms (since that contains the CJC IC), and nothing seemed to help much.
ADC said that the PLC power supply might be aging, and likely to show the first symptoms if that were the case would be analog cards. We changed the PLC and that seemed to cure it.
Created Date: September 23,2014
Created by: ControlsGuy
I was just having a very similar issue with a six-year old DL06 that had two F0-04THMs. My problem seemed able to strike anywhere, it wasn't consistently with one card.
We looked at the cabling since it had been redone fairly recently, swapped the cards (since at that point it did appear confined to one card), swapped the wiring arms (since that contains the CJC IC), and nothing seemed to help much.
ADC said that the PLC power supply might be aging, and likely to show the first symptoms if that were the case would be analog cards. We changed the PLC and that seemed to cure it.
Created Date: September 23,2014
Created by: a agnone
Thank you for the comments. I will try the connecting of the (-) of the TC to ground and also check the PLC Power Supply. That PLC is like 10 years old.
Created Date: September 24,2014
Created by: Bob S BN
I will try the connecting of the (-) of the TC to ground
Don't do this if you are using TCs with a grounded junction.
Created Date: September 24,2014
Created by: steveola
Ungrounded thermocouples are the way to go. The grounding may give a faster temperature response but it never seems to go well for me when the junction is grounded.
Created Date: October 01,2014
Created by: GlennLee
Solution I have used to quiet a T/C input.
Hi All. I sometimes have Thermocouples that cannot be made quieter by the usual methods. what I HAVE done to make them quieter is to add a 10 microfarad Tantalum capacitor across the terminals at the thermocouple card. I put the positive leg of the cap to the "+ " input and the negative leg to DC common. It does not seem to affect the readings and dampens the noise nicely.
ONLY USE TANTALUM CAPS! NOT ELECTROLYTICS!
Created Date: October 01,2014
Created by: bfitz
Glenn,
Does that affect the burnout detection circuit?
Created Date: October 01,2014
Created by: GlennLee
T/C filtering and burn-out detection
Hi. I 've never tested the burn-out feature. The Tantalum caps present an open-circuit to the input and do not generate a voltage like the thermocouple does so it should not affect anything but noise-related issues.
Created Date: December 26,2014
Created by: primus
F2-04THMs
Hello
a agnone - in your post you did not say what type of process you are attempting to control.
I had the same problem several years ago, in my case I was controlling the temperature of an oven. In my application the K-type thermocouples were mounted directly on the heating element (calrod heater) I called AD, Facts ... used software filter, averaging filter, changed from grounded to ungrounded thermocouples, wiring for thermocouples were all separated from any high voltage lines, pretty much done everything I could and that was suggested. Although I did not try GLennLee suggestion of using a 10 microfarad Tantalum capacitor now I did try a capacitor but not sure if it was Tantalum.
Hmmm maybe when I have some time I may try that.
Anyways I finally reached someone at AD or Facts that seemed to have more of a handle on my problem it seems that at the temperatures we run our ovens the heater gain stress fractures and emit a lot electrical interference too much. So I used different temperature controllers and used the plc (260 processor) to communicate using Modbus rtu.
Hope This Helps
Tom