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Guest chuckm

Allen Bradley 1746-BTM

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Has anyone had any experience with the Allen Bradley 1746-BTM barrel temperature module. We started using them approximately 3 years ago with no problems. Lately however strange things have been happening that we can't put a finger on. On occaision, we had the temperatures on all four loops indicate negative temperatures on machine startup. If the operator notices this, and shuts the power back off and turns it on again, it goes away. If they don't notice, the barrel temperatures try to heat to setpoint and because the temperature stays negative it overheats. This negative reading is the same reading I get if I simply disconnect the thermocouple from one of the loops. However the temperature will return to normal when I hook the TC back up. When they go negative on their own though, they stay there until power is cycled again. I don't believe it is code related as the BTM code is the Allen Bradley code downloaded from their site and has been unchanged by us. Also I don't think it is code related because I can't get the problem to go away by cycling the keyswitch on the 5/03 to program then back to run. Where I am leading to is perhaps noise issues or shielding problems. I also have a 1746-FIO4V, a 1746-NI8 and a 1746-NT4. If I disable the NI8, I have yet to get this to occur again. But of course I can't run the machine without the NI8. Also, I am now beginning to hear reports that this is starting to happen to the machines when they are running, not just when turned on. And it is not isolated to just our facility. While it was at one time, it is now starting to happen at four seperate locations separated by many states. I was hoping that perhaps someone else has had this problem and has found a solution. Thanks in advance.

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Well if you're sure it's not software...check your wiring..seems awfully simple but my experience is it's always the simple things....especially when the probelm is getting worse...loose, corroded, connections etc. broken wire inside the insulation jackets....

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Had similar problem happen with a modicon and thermocouple inputs...The T/C inputs didn't like to see grounded thermocouples... As it turned out we found out this problem occurred when an electrician changed a "BAD" (questionable) thermocouple and made the problem worse by installing a grounded thermocouple insted of a non grounded thermocouple. It turns out the grounded T/C picked up noise from ground and injected it into the T/C module causing funky things to happen. We changed the T/C's back to non grounded types and "Wala" the problem went away! Good Luck!

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Thanks Jimmy! That sounds like an excellent avenue to explore. http://www.omega.com/techref/themointro.html I am not sure, but I would almost bet that our thermocouples are grounded. I will indeed check with our supplier tomorrow and get all the specs on the TCs we use.

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