Can I synchronise compactDAQ and M-series DAQ card for continuous non-regenerating waveform generation in RT

[AnthonV]

Hi, 

I'm using a M-series DAQ card (6229) to do multichannel and multipoint reading and writing of waveforms, all synchronised to a clock generated on the 6229.  Now I need to extend this to a 'remote' (10m away) location and I was considering using the Ethernet CompactDAQ (9188 or 9184) or maybe the 9144 Ethercat slave chassis.  Before I buy and learn the hard way I thought I'd ask for some advice:

My questions are: 

1) By using DAQmx can I access the I/Os on the 9184 or 9144 transparently using a multi-channel multipoint DAQmx task as I do for the 6299 PCI card?

2) Are all these chassis supported if I use RT on the host?

3) Is the best way to synchronise and trigger the remote system to the host by running a digital line from the plug-in 6229 to the remote chassis, and if so, how do I connect it to the chassis and define it as a sample clock?

Any help would be appreciated.

[Blake-C]

I wanted to let you know we've got someone working on answering your questions. I've posted answers to the first two below, but since that changes 3) a bit, I'm talking to some colleagues about the best way to go about implementing your application.

1) No, you won't be able to access I/Os like you do with the 6299. The 9184 and 9144 are chassis that support modules and the 6229 is a card seated in the computer and they interface differently.

2) These chassis are not supported in RT.

I hope that helps, I'll get back to you soon with an answer to 3).

[AnthonV]

Thanks for the feedback Blake,

\What do you mean that these chassis are NOT supported in RT.  Do you mean that if I have a Desktop running RT then I cannot connect these chassis via an ethernet cable and read and write to the I/Os on the cseries modules on the chassis?  

[Branch_Support-NIC]

Hi AnthonV,

There is no CompactDAQ chassis (USB, Ethernet, Wifi versions) support with LabVIEW RT systems, as per this DevZone article. The 9144 is a different platform which requires a supported EtherCAT controller. A PC running LabVIEW RT with NI-Industrial Communications for EtherCAT 2.0 or higher qualifies, according to this KB. The readme for the EtherCAT software also lists the folloing requirement:

• Real-Time Desktop target with any of the following Ethernet interfaces

– NI PCIe-8231

– NI PCI-8232

– NI PCIe-8235

Please note that as long as you follow the requirements for the PC running LV RT (2nd link) then you should not need the NI Ethernet interfaces listed above, but these are the only configurations that have been officially tested. Hope this helps!

[Tom_W_[DE]]

Hi AnthonV-

I'd like to correct a couple of comments on the CompactDAQ chassis questions.  I am not an expert on EtherCAT or the 9144, so I'll hope and assume that the previous post is sufficient.

First, as of NI-DAQmx 9.6 (and later), USB CompactDAQ chassis *are* supported under PharLap RT, except for the first generation cDAQ-9172.  This means that you can use the cDAQ-9171, -9174, or -9178 chassis with a LabVIEW RT desktop, RT PXI(e), or RT Industrial Controller that is running PharLap LabVIEW RT.  Also, the cDAQ-9138 and cDAQ-9139 are stand-alone CompactDAQ chassis that are capable of running LabVIEW RT.  Unfortunately there is no ethernet or wireless CompactDAQ support (for cDAQ-918x or cDAQ-9191 chassis) available on PharLap RT.  So, your question about whether or not you can connect an ethernet cDAQ chassis to your RT Desktop and access the I/O is unfortunately a 'no.'  I will request an update to the linked DevZone article to correct the information on USB CompactDAQ support under PharLap LabVIEW RT.

I think your question on reading I/O points in a single task might have been misunderstood (by me or others 😉 ).  Are you asking whether you can insert the module configuration that you need in the chassis and then combine I/O into single tasks for Analog Input, Analog Output, etc, across different C Series modules?  If that is what you're asking, the answer is 'yes,' as long as the I/O type is the same for all channels in the task, much like what you'ure used to with your M Series card.  If you are asking whether a single task can contain channels from both the M Series device and modules in the cDAQ chassis, the answer is unfortunately 'no.'

Hopefully this helps-

[AnthonV]

Thank you for the information. The last time (some years ago) I checked it was best to turn *off* the USB support in the BIOS on an RT desktop to improve latency and real time performance, but that seems to not be an issue anymore if the compactDAQ can be connected via USB to the RT system.

I am glad to hear one can have multi-channel tasks (as on a plug-in 6229). I am only planning on using channels on the same c-series module in a tasks.

Now what I *really* want to know is - can I do n-point writes to such a task? So in the same way that I can set up a task on the m-series 6229 card to start on a trigger, and then to clock out samples on a clock (say a 1ms counter event), and then I write to the task e.g. 100 ms worth of data and it happily clocks out this data every 1ms and I just ensure that I do a multi-point write before the data is all written out.

Can I do this on the compactDAQ, or, if I need samples to update every 1ms, do I need to have a 1ms loop on the RT system writing single point data every loop iteration?

Am I rambling on or is this question making sense?

[Tom_W_[DE] · Accepted solution]

Hi AnthonV-

You're making perfect sense.  And, I'm glad to report that you can program your CompactDAQ-based analog output task to use a hardware-timed clock just like your M Series device.  In fact, it's possible (and maybe even likely) that the same NI-DAQmx code you use for M Series could be used directly on CompactDAQ as long as the AO channels, trigger and timing sources, and the like can be updated to point to your CompactDAQ chassis.

As I mentioned before, please be aware that only USB CompactDAQ chassis (excluding the cDAQ-9172) are compatible with PharLap LabVIEW RT targets.  I'm not sure if this will meet your needs for a >10m extension from the host system.

[AnthonV]

If I want to synchronise the compactDAQ and the 6229 (i.e run both of the same clock signal), I suppose I could route the 1ms signal (counter event) on the 6229 to one of its digital output lines, and then connect this to a digital input on the compactDAQ and make this digital input a clock source for the compactDAQ's task?

Your comment is correct, 10m is out of USB's recommended range so I probably wouldn't be able to make use of the compactDAQ (unless Ethernet support is imminent - any insights?).

So it seems I need to look at the ethernet/ethercat Expansion Chassis. Is it corrent that none of the DAQmx constructs then apply? With the expansion chassis is access to the I/O on the chassis similar to the way it is done on a cRIO controller - either through a scan engine or through a FPGA reference?

Thanks for the advice.

[Tom_W_[DE]]

Hi AnthonV-

Yes, you could use the scheme you described to route timing signals from your M Series card to a CompactDAQ chassis, either through a digital I/O C Series module or through the BNC PFI lines on the chassis (only applies to 8-slot CompactDAQ chassis).  Ethernet support is definitely not imminent; in fact, we do not have scheduled plans to support it as of today.  If you need that support in the future I would encourage you to lodge a request with your local NI sales engineer.

As for the expansion chassis route, yes, you would have to use LabVIEW FPGA or similar because the NI-DAQmx API calls wouldn't be relevant to that hardware.  Unfortunately my expertise is fairly thin with non-cDAQ chassis, so I'll have to defer to another poster on any specific questions you might have.

Hopefully this helps-

[AnthonV]

Thanks for the help on CompactDAQ.  I'll do more digging on the Expansion chassis too.