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PCIe-6259 anallog input clipping (possibly overvolting) effect on other anlaog in channels?
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CRF450_ Kev
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01-27-2011 09:41 AM
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Curious if clipping/possible ovevolting on one of the analog in channels would negatively affect performance of other analog in channels. I have two systems, one where signals don't clip and the other channels are still useable. The other has some clipping issues (which will be cleared eventually btw) on some of the anlog ins. The one with clipping on other channels are seemingly unuseable while the ones that have no input clipping seem fine.
I seem to be experiencing a situation in which clipping on one analog in channel makes it so other analog in channels aren't working.
Curious to know if I'm seeing what is expected?
anybody have any insight here?
Is this how it is supposed to be working?
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Accepted by topic author CRF450_ Kev
rbohacek
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01-27-2011 12:24 PM
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We do not guarantee that all channels will work normally when one is in a fault/over-voltage condition.
Since this is a MUX'ed architecture the channels are scanned sequentially into the shared instrumentation amp and ADC. If the instrumentation amp is railed for channel 0 (for example) it will take some time to recover from that fault after the next channel is switched in. This may cause a number of the following channels to be incorrect (possibly shown as being railed).
Obviously we do not recommend operating this device in a fault condition. When you says "analog channels aren't working" what do you mean? Is the data railed?
Some things that might help:
- Sample slower allowing the instrumentation amp more time to settle
- Skip the offending channel in the scan list
- Make sure the offending channel is set to the largest voltage range (+/-10V)
01-28-2011 12:07 PM
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Sorry for the delayed reply.
We do not guarantee that all channels will work normally when one is in a fault/over-voltage condition.
Since this is a MUX'ed architecture the channels are scanned sequentially into the shared instrumentation amp and ADC. If the instrumentation amp is railed for channel 0 (for example) it will take some time to recover from that fault after the next channel is switched in. This may cause a number of the following channels to be incorrect (possibly shown as being railed).
Actually this makes alot of sense to me and what I suspect must be happenning. Thanks for the insight.
Obviously we do not recommend operating this device in a fault condition.
The conditions when this has been observed are during a pre installation test stage where all but the channel under test are fairly long lead length unterminated, unshielded, and left flapping in the breeze. In other words a worst case situation which gets much better when the system gets installed to the customers facility.
When you says "analog channels aren't working" what do you mean? Is the data railed?
Yep. It is popping in and out of the rail synchronous to the noise on the other channels.
Some things that might help:
- Sample slower allowing the instrumentation amp more time to settle
- Skip the offending channel in the scan list
- Make sure the offending channel is set to the largest voltage range (+/-10V)
I have a solution for the problem. I was just trying to gather as much info as possible to make sure to make the best choice as to what the solution should be.
I very much appreciate the valuable reply.
Good Day.
Kevin.
