I hadn't really thought to ask about possible external sources. The really bad thing about intermittent problems is that it is often very hard to 'capture' them.
You could use a line filter on the AC input to the 24VDC supply to help things.
P.S. Gene, is there ever a time when you are simultaneously (sp?) swithing several of the DO? This might represent a worst case situation for noise generated by the output loads.
So we lost a module again after adding flyback diodes to the the outputs of the 401. I am trying ot find a source for the parts you TVSS you listed and and they is a 2 month lead time and a 12 part minimum order. Can you recomend an alternative or a source that you use?
In going through the process of setting up an order with the Littlefuse product that I linked you to previously, it looks to me that you can order as little as one, and the ship time is immediate. On our end it looks like each of these products can ship right away. Also, I would just like to reiterate that these were designed for 24V power supplies.
I attached the TVSS to the 401 module a couple weeks ago and so far so good. I really wanted to see proof that the spikes were cleaned up so I ran a couple put a couple of short wires on the + and com on the CB-1 module. Before adding the component I was seeing 20 to 30 V pk-pk decaying oscillation any time the 401 switched any of our heavy loads(480VAC pumps and AC to DC converters). These signals were about 300 nSec long. After adding the TVSS I saw little change in the signal. After a couple of hours of rerouting wires to give more isolation between the 24VDC and 480VAC, several right on top of each other, I was able to reduce the Amplitude of the spikes slightly and reduce the occurrence by ~%60.
My plan is to add the TVSS into all new and existing systems as it is cheap protection. Next when the problem system can be shutdown we will remove the 480Vac from the proximity of the Control System by moving it to it's own enclosure. At this point I expect to see almost all of the noise spikes go away.
We started seeing this same problem in the field too. The TVSS seemed to fix the problem for the 401s. Are the TVSS only necessary for the 401 or should they be placed between the V and C terminals of all Fieldpoint cards (analog ins/outs, digital inputs, and ethernet controllers FP-1601)?