Unable to set maximum sample rate when using SAR NI 9223 module and Slow Sampled NI 9219 module in cDAQ-9174 chassis

[glstill]

Hi,

I have a cDAQ-9174 4-slot chassis with a NI 9219 and NI 9223 connected.  The NI 9223 is a simultaneous SAR device capable of sampling at 1 MS/s.  The NI 9219 is a Slow Sampled device capable of 100 S/s.  The C-Series device listings are here:

http://zone.ni.com/reference/en-XX/help/370466AE-01/mxdevconsid/cseriesnames/

I am using a single task with a channel for a temperature measurement from the NI 9219 and a channel for a voltage measurement from the NI 9223.  The slow-sampled device is supposed to replicate data when configured at a higher sample rate if it is in a multi-slot chassis as described here:

http://digital.ni.com/public.nsf/allkb/A8257C9D58DA55E486257DD6005ECDC6

The data replication works fine when i specify a sample rate over 100 S/s up to 100 kS/s, but when i set the sample rate higher, a DAQmx error is generated:

error -200019

ADC conversion attempted before the prior conversion was complete.

Increase the period between ADC conversions. If you are using an external clock, check your signal for the presence of noise or glitches.

I have read a lot of information including this link below :

http://www.ni.com/tutorial/5376/en/

which states....

Two SAR/Slow Sampled Modules - When two SAR modules, SAR and Slow Sampled modules, or two Slow Sampled Modules are placed in the same hardware timed task, the DAQmx driver shares the same chassis or controller’s sample clock and start trigger between both modules. For the SAR and Slow Sampled Module configuration, the maximum rate that data is returned is not determined by the Slow Sampled Module. The driver will return duplicate samples for the Slow Sampled module to allow you to run the SAR module at the fastest allowable rate.

Thus I am trying to understand why the error is being generated.  I would like to measure my voltage input at 1 MS/s and also perform a temperature measure with the NI 9219 and simply have extra samples that are replicated for the temperature measurement.

Do i need to tell the NI 9219 to operate in high-speed mode?  Is there anything I can do to fix this issue?  Or is there a limitation that I am not understanding?

Thanks,

Gary

[CFER_STS]

The specifications on the NI 9223 datasheet indicate a maximum sampling rate of 350 kS/s using FPGA IO nodes, which corresponds to a period of 2.857 us.

You can speed this up to 1 us acquisition by separating acquisition and data transfer using User-controlled I/O sampling:

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z0000019Km2SAE

[glstill]

Hey,

Thanks for that feedback.  The specifications also say 1 MS/s for CompactDAQ and I can run at 1 MS/s when I am not including the NI 9219 in the task.

Any thoughts?

Thanks,

Gary

[GerdW]

Hi Gary,

Any thoughts?

What about using two tasks?

[glstill]

Thanks for the suggestion on trying two tasks.  I gave that a try and got the same error.  But going down that path, I did learn that the same error occurs when I simplify to only have one task with a single channel for the NI 9219 thermocouple measurement.  It will repeat the data for sample rates up to 100 kS/S, but the error is generated at higher rates (e.g. 150 kS/S or higher).  So the question is why does the repeating of data work up to a specific sample rate.  It seems that repeating should be allowed for any sample rate higher than the devices 100 S/s specification.

Gary