Control Logix Digital Input Card Problem

Hi Experts,

I would like to share one prb with you experts, on one of my site i have Control Logix Redundant System with 2 I/Os Chassis. I have 3 Digital Input Cards(24V DC) in both my chassis , but during last evening i have experience very unusal activity. One each DIs Module in both the chassis experience loss of input signal from different switches which causes ESD. This system is running for around 10 years and this is the first time we have experience this problem. On investigating i founded out that the solar panels which are providing the Power source to PLC Panel doesnt have the ground at its end. Is this can be the actual problem for the only 2 DIs Input Cards to behave abnormally.

Regards,
Sam Khan

It may be that you have a batch of faulty cards, recently I had a baffling problem with an analog one.
Occasionally after powering down the panel one analog card would fail to give any output, at first I put this down to spikes when powering up, however I tried filters constant voltage psu's etc, none made any difference, although powering down & back up a few times would kick it back into life I replaced the card and not had any problems since I remember having a similar problem on a S5 Siemens system (new)inputs would randomly switch on/off Siemens rejected the idea that the cards were to blame, however we had some spare old ones removed from an old system, replaced them & no more problems, we sent the cards back to siemens & they confirmed a batch of chips were "out of spec" & estimated over 400 units they had sold may have timing problems, they scrapped the cards & sent replacements.