I am currently troubleshooting a Micrologix 1400 model 1766-L32BXB PLC. Even with no input wires connected to "in12" through "in19", the unit is reading 24 volts when powered on. Could this indicate a malfunctioning PLC? Thank you for your help.
When testing voltage potential on PLC input terminals (such as COM 3 for IN12 to IN19), ensure a wire is landed on the COM terminals for proper reference. Without a proper reference point, it is difficult to accurately measure voltage on the PLC inputs. Make sure to check for the presence of voltage only after the wiring is securely connected to both the input and its associated COM terminal to avoid any discrepancies in readings.
Each input group of the ML1400 can be wired as sinking or sourcing. When wired as sourcing, you should expect to measure a voltage on the input even when nothing is connected to it. In other words, this is essentially checking COM 3. If wired as sourcing, a 24V wire should be present.
I apologize for the confusion, com 0-3 are interconnected. The input banks only receive voltage when connected to a sensor, and this particular bank is the only one where voltage is present at the input terminals.
Last year, there was an issue with a 1400 unit where the inputs in a group were displaying voltage even when field devices were disconnected. Upon investigation, it was determined to be an internal electronic failure within the unit. The unit was promptly replaced thanks to the warranty coverage.
This sounds like it could be a problem but it's also important to consider other factors. Have you tried testing it with different multimeters to ensure there isn't an issue with your measuring equipment? It could also be a sign of a ground loop or possibly an induced voltage given that you're reading 24 volts even without any input wires connected. In case these situations aren't applicable, then yes, your PLC might be malfunctioning. Maybe try resetting it or check for any additional symptoms that could provide more clues. Remember, diagnosing PLC issues can sometimes be a process of elimination.
It certainly could be a sign of faulty PLC, but before coming to any conclusion, I would suggest re-checking your wiring. Sometimes, a short or an accidental connection elsewhere in the system can cause a "false positive" voltage reading. Also, try to isolate spots where there might be potential electrical interference. If you've exhausted all these possibilities and still seeing the error, it might be a failing PLC. In that case, contact your manufacturer or your vendor for a comprehensive diagnostic or possible replacement.
It does indeed sound like an issue with your PLC. Typically, these inputs should be reading as 0 volts when not connected. However, before concluding that the PLC is malfunctioning, I'd suggest checking the wiring and terminal block for any possible shorts or faults in the I/O module. In case you still observe the 24 volts reading, you may need to consider replacing the PLC or sending to an authorized repair center. Remember, always stay safe while troubleshooting!
It sounds like you might be dealing with a problem related to either a grounding issue or a stray voltage on the inputs. Sometimes, if the inputs aren't properly grounded, they can pick up voltage from nearby sources, which could explain the 24 volts you're seeing even without connections. Iād suggest checking the wiring and grounding first, and if those look good, considering the possibility of a malfunction in the PLC itself or any internal circuitry issues that could be causing false readings. Good luck with your troubleshooting!
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Answer: 1. Q: Why is my Micrologix 1400 model 1766-L32BXB PLC reading 24 volts on inputs "in12" through "in19" with no wires connected? Reading 24 volts on the inputs without any wires connected could indicate a potential issue with the PLC or the input module. 2. Q: How can I troubleshoot the input voltage issue on my Micrologix 1400 PLC? To troubleshoot the input voltage issue, you can start by checking the wiring connections, ensuring proper grounding, and testing the PLC with known working input modules.
Answer: It is not common for a PLC to register a voltage reading on input channels with no wires connected, which suggests a potential problem with the unit.
Answer: If the PLC persists in displaying 24 volts on the inputs without any connections, it may be necessary to further investigate the issue by consulting the PLC manual or contacting technical support for assistance.
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