Channel Overloads on 446x and 4498 Modules

[DudeWayne]

I would like to understand better what the DAQmx driver call for Channel Overloads does.  I understand that one must first call the ChannelOverloadExist(), and only if this returns True should you query the actual Channel overload list.  But here are my questions...

1) When does the overload flag for each channel get reset?  Is it based upon the starting/stopping of a task?  Is it based on performing the function call ChannelOverloads?

2) If you are acquiring data continuously, what does the channel overload data mean?  And, when do the overload flags get reset?

3) What amount of head room exists above the voltage range settings before a signal hard clips?

I ask these questions because the list of Overloaded channels I'm getting do not appear to have signal levels that should trip the overload condition.

[Mr.F]

Hi Dude,

If you look in the help for the ChannelOverloadExist() call, reading this will clear the overload status for all channels in the task. Page 2-6 of the DSA User manual

http://www.ni.com/pdf/manuals/371235g.pdf

 has very good description of how both analog and digital  overload conditions can occur and this is most likely the reason you may detect and overload condition but don’t observe clipping. Take a look at that section of the manual and let me know if something is still unclear.

[SKowl]

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1) When does the overload flag for each channel get reset?  Is it based upon the starting/stopping of a task?  Is it based on performing the function call ChannelOverloads?

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Any time you read the OverloadedChannelsExist property, the overload state of channels is read and immediately cleared.

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2) If you are acquiring data continuously, what does the channel overload data mean?  And, when do the overload flags get reset?

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Channel overload data should be discarded, as you could be reading a clipped signal.

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3) What amount of head room exists above the voltage range settings before a signal hard clips?

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From the DSA manual that Matt linked to in his reply, it appears the overload point is 10.7Vpk for 446x and 449x devices.