KathyPatrick

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  1. Question from a PLC newbie....  We had a "blip" during a thunderstorm where we saw multiple signals on a 1734-IB8S point I/O transition from true to false for ~ 4 seconds (based on our DCS history from a serial connection).  There are several other modules on the backplane, and we only saw state change on this one card.  The 24VDC power is sourced from T-0 for points 0-3, and T-2 for points 4-7, so we don't suspect a short.  It's been suggested that we either had an I/O card "blip", or temporary loss of power to our field contacts (limit switches) caused by dust/vibration of the removeable terminal block.  Our controller is a 1756-L73S GuardLogix 5570.  My question is should I expect to see an I/O fault in the Minor Fault history (we did not)?  Would an I/O fault necessarily show up in this history, or does it need to be configured somewhere? Our points on this card are set up as single points with test pulse from T-0 and T-2.  We are reading status of limit switches in the field. Thank you in advance for any response. Kathy