Multifunction DAQ
PCI express alternative to PCI 6602?
Hi thomas03,
NI does not have a dedicated PCIe counter/timer card. However... the X Series Multifunction products include 4 counters (as opposed to 8 on the 6602) which have more functionality than the ones on the 6602. If you just need to measure 4 detectors and don't have any analog requirements, a single PCIe-6320 should be all you need (it's the lowest-cost X Series). The counter features are identical across all X Series cards.
Assuming you are using DAQmx already (as opposed to Traditional NI-DAQ), then the X Series card uses the same driver as the 6602 and caveats should be minimal. Some of the relevant differences:
- The X Series cards do not have an 80 MHz timebase, but instead a 100 MHz timebase. The 20 MHz and 100 kHz timebases are still present.
- The X Series card only has 4 counters instead of 8.
- The first sample is discarded when performing a buffered period measurement (image below is for semi-period measurement, but hopefully it shows the idea. 6602 / M Series behavior on the left, X Series behavior on the right):
The X Series throws away the first sample since it is not truly a measurement between two rising edges since the counter is armed asynchronously to the input signal. If this is an issue, you could instead configure a buffered edge count task to work around the behavior.
Your 3 MHz on 4 channels should be sustainable on the PCIe X Series. In addition to the faster bus, the X Series boards have an on-board FIFO for buffered counter measurements. Sustained rates have been benchmarked up to 10 MHz on all 4 counters. The switch between busses should not introduce any complications to the application other than the differences in hardware that I have mentioned above. If your 6602 application is written in Traditional NI-DAQ then you'll need to re-write the application in DAQmx. You will of course need a computer with a PCIe slot to use the X Series :).
Best Regards,
Hi Thomas,
In your case I'd probably recommend starting with the Counters section (Chapter 7) of the X Series User Manual--it doesn't give any advice about how to program the counters, but it does give an excellent description of what the hardware is capable of. Step 1 is to figure out what mode of counter task you want to use to implement your functionality (I suggest using an Implicitly-Timed Buffered Period Measurement).
From there, it's a matter of turning your desired functionality into workable software. The DAQmx Help (which unfortunately is not searchable online) provides more information about how DAQmx implements various hardware-specific features, but it is not ADE-specific. For example, one of the first things you might notice is that the hardware refers to "Gate" and "Source" inputs, but DAQmx abstracts this from the user. The following table from the DAQmx Help (Counter Parts in NI-DAQmx) gives more insight to how to refer to the terminals in DAQmx (a period measurement is an example of a "One Counter Time Measurement").
Once you are familiar with general DAQmx concepts and features, yet another step is to determine which ADE-specific functions should be used to implement the desired behavior. That's where the C Reference Help and Shipping Examples come in.
In short, you're absolutely correct that the resources are much too spread out and disjointed. There is quite a bit of information available in the various help files, but it can often be difficult to locate. I know that NI does have a team working to publish the DAQmx Help and C Reference Help online in a searchable form, so hopefully that will make things easier in the future. Sometimes it's best to just post to the forums or contact NI Support when in doubt so people who have been through it before can point you in the right direction.
What I'd suggest you do is start out with the "Dig Periods-Buff-Cont-High Freq 2 Ctr", since it almost has everything you need already. You do need to make some modifications to the create channel however:
DAQmxErrChk (DAQmxCreateCIPeriodChan(taskHandle,"Dev1/ctr0","",0.000001,0.100000,DAQmx_Val_Ticks,DAQmx_Val_Rising,DAQmx_Val_LowFreq1Ctr,0,0,""));
You will also probably need to increase the number of samples read per loop since your data is coming in so quickly. You might possily also need to increase the DAQmx buffer size using DAQmxCfgInputBuffer, or by increasing the sampsPerChanToAcquire input of DAQmxCfgImplicitTiming.
By default, the period task will use the default GATE PFI line as the external signal to be measured in terms of ticks of the internal 100 MHz timebase. The default terminals can be found in the DAQmx Help, but I'll post it here as well for convenience for the 6320:
If you want to change the terminal to be used for your gate, you can do so with DAQmxSetCIPeriodTerm. If you want to change the terminal used for the source, you can use DAQmxSetCICtrTimebaseSrc. If you want to continue using the 20 MHz timebase, there is one available on the X Series, but I'd suggest sticking with the 100 MHz default to give more resolution on your timestamps (especially if the input signals are coming in at 3 MHz).
Best Regards,
