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How can I quickly sample data from 200 channels using DAQmx?

Hello,

 

I am trying to sample thermocouple data using a SCXI 1000 chassis with two SCXI 1100 modules and one SCXI 1102B, all of which have a 1300 isothermal terminal block. The computer I am using has a PCI-6052E DAQ card and 1 GB of RAM. I will eventually need to upgrade to a SCXI 1001 chassis with enough modules to collect about 175-200 different signals. The problem is I am testing with just the 96 channels I have available and the program runs super slow, with the maximum sample rate only .026 Hz. Currently I have all the channels being read by one DAQmx VI. I've looked through the example programs and tutorials, but nothing there deals with large numbers of channels. Is there a way to improve the sample rate to around 1 Hz with so many channels?

 

Thanks in advance

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Check the filter configuration for your SCXI-1100.  The product page says that if you set the filter for 4Hz, you'll only get 3 Samples/second.  The slowest module in the chassis determines the sample rate.  If one of your modules is configured that way, you'll get a maximum rate of approximately 3 hz / 96 channels = 0.031 hz/channel, which is pretty close to what you've reported.  The filter is set by a jumper on the module, see the manual under "filter selection."

 

You might want to look at "Determining Maximum Scan Rate for Multiple SCXI Modules" as well.

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I checked the configuration and the SCXI-1100 were both set to filter at 10kHz. I tried changing the physical locations of the SCXI modules in the chassis, and I found out one of the SCXI-1100s in MAX had a filter setting set to 4Hz. Apparently the software setting overrides the jumpers, because once I switch it to 10kHz, the program ran much faster. Thanks for the help!

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Hi BBalmforth,

 

The software setting doesn't quite override the jumpers: they both matter. The jumpers on the SCXI-1100 control the filter cutoff frequency, regardless of what filter setting you specify in MAX. However, the SCXI-1100 hardware doesn't support detecting the jumper settings in software. DAQmx requires you to use the filter settings in MAX to tell it what the jumpers are set to, so it can calculate the correct maximum sample rate and filter-based delays.

 

Brad

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Brad Keryan
NI R&D
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