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output of FieldPoint 401 module does not go low

I had a chance to check out most of the signals with a scope and never saw any kind significant spike.  Rarely I saw a 5 to 10 volt spike.  It has been a bit of  a mystery as we have never seen the the spike that is causing the problem.  I did a little more research and believe the problem may be coming through the AC Side and going through the Power supply.  We have MOV's on all AC relays in our system but as it turns out there are some large pumps on the the same AC as us that have no suppression.  My plan of attack is to use one of the suggested suppressors on the V1 to common, and one on the V+ to common on each of the CB-1 modules.  Any other suggestions?  We have lost 10 401 modules to this issue, so a little overkill is a good investment.
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Message 11 of 21
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Gene,

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.



Message Edited by centerbolt on 12-14-2007 05:02 PM
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Message 12 of 21
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Jason,

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?

 

Thank You!

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Message 13 of 21
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Gene,

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.

Jason W.

National Instruments
Applications Engineer
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Message 14 of 21
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We have had a similar problem, and have lost 6 boards so far on 3 installations.  After reading this board, we just ordered some of the TVSS that were linked above.  Did UPS next day delivery and got them right away.  We ordered Mouser stock # 511-P6KE27A at $0.20 each (minimum order qty was 1, but we got 10).  I am going to hook them up right now.

Jason, when hooking these up, are they being hooked up to the V and C terminals on my CB-1 connector block (for the DO-401 board)?
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Message 15 of 21
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Hi Anaerobesys,
 
The products that were listed are for use with 24V power supplies, hopefully that is applicable to your situation. 
 
You are correct in the location of the TVSS.  To prevent against this type of failure you will need to attach a properly selected transient voltage surge suppressor between V and C.  To hook this up to the DO-401, connect the side of the transient voltage suppressor with the line/bar to the V terminal on the terminal block, and then other end to the C terminal on the terminal block.
 
Let me know if there is any further clarification I can provide.  Have a great day!
 
Jason W.
National Instruments
Applications Engineer
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Message 16 of 21
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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.

Message 17 of 21
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After attaching the TVSS, I too stopped blowing the boards.  This was an easy and inexpensive fix.  Thanks!
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Message 18 of 21
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Jason,

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)?

Thanks

Damien

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Message 19 of 21
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Hi Damien,

Using TVSSs with your other FieldPoint modules will certainly not hurt them, but they should not be necessary.  The [c]FP-DO-401 modules are particularly susceptible to transient damage, as can be seen from the caution on page 11 of the manual.  I have not noticed a similar caution for other FieldPoint modules, but to be safe, you should always consult the manual before operation.
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Message 20 of 21
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