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Old January 14th, 2022, 11:37 AM   #1
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lofiwizard is offline
Join Date: Dec 2019
Location: Ferndale
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Micrologix RTD 1762-IR4 Reads as 0 Ohms before correcting

I have a Micrologix 1400 with an 1762-IR4 RTD. I use it to read airbag resistance on seats on an assembly line. I am often getting into a situation where it is reading as a short circuit, when there is not a short. Then it kind of just goes away after minutes. I can't find a rhyme or reason to it. Any ideas would be appreciated. When in this state, any resistance applied across the RTD inputs doesn't read correctly.
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Old January 14th, 2022, 06:54 PM   #2
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danw is offline
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Join Date: Oct 2004
Location: midwest, USA
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I am assuming that this used to work properly (no false zero Ohms readings). It sounds like you have tested the resistance module with a known resistance when 'the readings' are acting uip and that the module does not read the correct value of the test resistance.

The highest probablility is that the resistance input module is bad. Then there are far less likely things like intermittent backplane connections, or an intermittent power supply. It is highly unlikely that the PLC program is executing code that reports some other variable unless someone has been working on the program recently,

Replace the resistance input module.
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Old January 14th, 2022, 07:31 PM   #3
James Mcquade
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James Mcquade is offline
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Location: Nashville, Tennessee area
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Welcome to the forum.

be sure to check the rtd requirements as far as the in series resistance required for testing purposes. you also MUST have multiple resistance masters to check the rtd circuitry for quality assurance. Have you done a gage r & r study?
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