ConfigureSampleClock using Daq-9178 and Daq-9239

[joelb]

Using a compactDaq 9178 chassis with 9139 AI module.  How do you configure the sample clock in .NET (VB - ConfigureSampleClock)(or C)? 

I can not find any documentation to tell me how to use the 9178 chassis PFI0 as an external clock source for trigger Analog inputs on NI9239 module in the rack.

Looking for the "signalSource" string to use in the task.Timing.ConfigureSampleClock.

Joel

[MCOTO]

Hi,

Have you ever tried with the NI DAQmx C Reference Help?

You can find this useful tool in Start Botton >> All Programs >> National Instruments >>  NI-DAQ >> Text-Based code support. I would recommend you to take a look at:

• DotNET #.# Examples
• ANSI C Examples
• NI-DAQmx C Reference Help

Regards,

MCOTO

[joelb]

Thank for the reply.  I have gone thru all of the examples and reference manuals that I could find.  It appears that the CompactDAC 9178 chassis and Analog Module 9239 do not work with the PFI's on the chassis as advertised.  I used MAX to create an Analog Task then set the Trigger to "External" then selected from the combobox "/cDAQ1/PFI0".  I gave this a few seconds timeout so that the task would configure but never get any triggers (eventually timeout). 

When I click "Run" the task returns an "Error -200414 - Requested sample clock source is invalid"

The same task configuration works for PCI and USB multifunction devices... Just not for the CompactDAQ.  I have a call into support now... no response yet.

Thanks

Joel

[JaredRo]

Hi joelb,

The NI 9239 uses a delta-sigma analog to digital converter to achieve 24 bits of resolution.  Because of this, it operates off of an oversample clock of 12.8 MHz.  To have the NI 9239 operate from an external clock, you would need to import a 12.8 MHz clock.  The PFI lines on the cDAQ chassis have a specified bandwidth of 1 MHz.  Because of this, you will not be able to provide the module an external sample clock through the PFI line.

In the NI 9239 manual, it does state that "the module also can accept an external master timebase or export its own master timebase."  It is possible to import and export the internal 12.8 MHz timebase of the NI 9239, but this can only be done between modules within the chassis by routing timebases directly through the backplane of the chassis.

We do offer a cDAQ synchronization module which allows for the sharing of timebases across multiple cDAQ chassis.  The product page is below for your reference:

NI 9469 - Chassis Synchronization Module
http://sine.ni.com/nips/cds/view/p/lang/en/nid/210832

Note that this module is only intended for sharing timebases between chassis, not for routing an external timebase to a single chassis.

[zhm0204]

Do you have a USB DAQ card to work with a external sampling clock.   Like a USB 4431 but may work with a external sampling clock.

[Kevin_Price]

I don't know the cDAQ catalog particularly well, but there are plenty of cDAQ modules that *would* support a direct external sample clock.  Check spec sheets for a converter type of SAR (successive approximation register).

In my limited experience, 16-bit analog modules are likely to be SAR type while 24-bit modules are likely to be Sigma-Delta (or Delta-Sigma, both terms seem to get used interchangeably.)

-Kevin P