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1734-IB8S Input LED turns red.... Causes

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A point guard I/O safety module sometimes shows the RED LED's on the input after the device has switched.  What could be the cause of this?  Set up is dual channel, equivalent with 1 second            discrepancy.  Two solenoid valves operating making 2 independent limit switches when valves closed which are wired back to the module.  Module itself has been replaced and so have both limit switches (Festo cylinder reed switches)  This does not always go into fault, only sometimes but when it does show RED LEDs' the software shows module as healthy.  Disconnecting 24v supply and reconnecting solves the problem (inputs show as amber LED).  Any help appreciated.

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From the manual 1734-um013_-en-p.pdf,

1734-IB8S Safety Input Status Indicator

Off - Safety input is off, or module is being configured. Recommended Action - Turn on the safety input or reconfigure the channel, if desired.
Yellow - Safety input is on. Recommended Action - None.
Red - A fault in the external wiring or input circuit has been detected. Recommended Action - Check configuration, field wiring, and devices. If no problem found,
replace module.
Flashing red - A fault in the partner input circuit of a dual-input configuration has been detected.  Recommended Action - Check the field wiring and verify your configuration for the partner
circuit. If no problem found, replace module.

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Thanks for the reply, I had seen the manual PDF,  The machine is 7 - 10 years old so configuration must be o.k, the devices have been replaced as has the module.  Apart from replacing all the cables what other "fault in the external wiring or input circuit has been detected" could there be?  This fault condition does not occur every time the switches operate. 

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maybe there is some issue using a reed switch for this application. is it PNP/NPN type proximity switch mounted on the side of the Piston? I know this does not help you but using this type of switch with a Safety unit would not be classed as a safety switch. 

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Only thing that i can think of, (except if the cable is damaged) is the speed of the cylinders or one of them binding on something.

Sometimes there are counter and adjustable throttle valves on theese.

I know you have 1 second as discrepancy time which should allow for most binding in either one of the cylinders.

Uneven cylinder movements might be the cause of this only happing "once in a while"

But again... Same thing could a damaged cable :)

 

I am not sure that a diagnostic code is available, when you are using the dual channel conf on the input card... like it would when using the DCS block. 

 

Finding periodic faults can be a hassle, but i am hoping you will figure it our!

Happy troubleshooting :)

 

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