Compact 984 analog output modules


Thread Starter

phil dryburgh


A problem occurs occasionally, where the analogue output modules lock up with dire consequences with the variable speed drives been used. The last known analogue signal will drive the vvvf at the wrong speed which causes problems with the process. There are two sample station employed identical in design and layout.
The PLC and I/O are all mounted inside the one cubicle with the vvvf Toshiba drives as well as microwave detector evaluation boxes and other
equipment mounted in the vicinity. The DOL drives are mounted in a adjacent panel serrated by the stainless wall of the cubicle. The PLC is supplied by a separate UPS supply from a substation @ 100 metres away separate to any other supply used in this MCC. Simple things like a brown out or lighting faults in the area appear to cause the problem of the analogs locking up.
From what I have read, the system bonding and grounding could be the source of the problem. As well as the segration of cabling in the PLC panel is non existent. If anyone may have encountered similar problem or can throw some light on this problem it would be appreciated.


Phil Dryburgh
Hello Phil,

If you are using the DAU-204 Analog output modules then I have encountered the exact same problem.

In my application the lockup problem also seems to happen after a power bump.

I have verified proper grounding and everything seems to be correct.

As far as I have been able to determine the cause of the problem is the D/A converter on the card. After a power bump the D/A converter locks up and
fails to respond correctly. The only easy solution, I have discovered, to correct the problem is to cyle the 24Vdc external power connected to the card on terminal point 1. After cycling power to the card the D/A converter begins working correctly again.

I am planning to install a set of contacts between the External 24Vdc power supply and Terminal 1 on the card. After a power bump I plan to open the contacts for a couple of seconds and then close them again. This should clear the D/A lockup.

The odd thing, is that, I have more than one of these cards. However, this particular card is the only one the exhibits this behavior. Very strange.

Bradley G. Hite
Intertech Incorporated
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Teaching Practical Skills for a Technological World