NI 9237 & NI 9234 synchronization different rate cDAQ-9178

[mdelsol]

Hi,

I want to create 2 synchronized tasks using different rates in acDAQ-9178, one using the NI 9237 module at low sampling rate of 2000 / 2048 Hzand another using the NI 9234 at 50000 / 51200 Hz depending on the Sample clocktime base used. I tried sharing sample clock time base but I always receive sameerror:

(201088, Task contains physical channels on one or more devices thatrequire a different Sample Clock Timebase Source than the one specified. Do notspecify the Sample Clock Timebase Source. DAQmx will set the Sample Clock Timebase Source appropriately).

So it’s possible to due such thing?

Can some of this modules use the timebaseclock from the other without being in the same task?

There is another way to synchronize themin separate tasks?

Can a timebase clock generated from acounter be used for this purpose?

I wouldn’t like to do any down sampling.

Using LV 8.6 & NI-DAQmx 9.0.2

Thanks in advance,

Marc

[mdelsol]

 

Hi, it's me again and I'm little bit surprised that 10 days after my first post no one answered any thing. I really expected more from the forum.

  

As I think that this is an important issue I would like to insist, so if the first post is not clear please ask me. If you think that post is not in the best place we can try to solve this also.

  

I really think that the problem is on the DAQmx driver, as the chassis has 3 timing engines and works fine creating only one task. The chassis is also able to handle 2 DSA tasks simultaneously, but the driver is not able to share Sample clock time base between the 2 tasks.

  

If it’s a DAQmx problem it could be fixed for the following releases. I may be wrong with my assumptions so please if we work around it to clarify the issue will be great for every body.

Regards,

Marc.

[JesusG]

Hi,

I understand that you would like to synchronize a 9234 with a 9237, and run them both at 50 kHz.  It is my understanding that if you include both of these modules in the same task, the 9237 will run at the 9234 rates by default (see the following KB).  However, you can use a DAQmx Timing property node to specify the 9234 to use the master timebase of the 9237.

Regarding the task configuration, this change was brought about in order to make DSA synchronization easier for users.  You can still configure the devices manually using separate tasks if you want to, but it is more of a manual process and there is more chance for error.  If you configure them manually, you need to make sure to use the appropriate property nodes to share the timebase, trigger and sync pulse.  Channel expansion in DAQmx takes care of this for us.  NI decided to add this functionality to cDAQ, S-series, X-series (although sync pulse is not used with these devices).  See the following link for more information.

Synchronizing DSA, S Series, and X Series Devices With a Single NI-DAQmx Task

My understanding is that we can pick up any rates for an externally imported master timebase, as long as a value between 0.391 to 52.734Hz to NI-9234. As explained on page 17, "When using an external timebase with a frequency other than 13.1072 MHz, the NI 9234 has a different set of data rates."

OPERATING INSTRUCTIONS AND SPECIFICATIONS NI 9234, page 17
http://www.ni.com/pdf/manuals/374238c.pdf

On this specifications, I could not find any part stating about a restriction of frequency of externally imported timebase f_M in the equation on page 16. So, based on the statement on page 17, I am guessing we can pick up any rates for f_M of external clock, and the set of data rates based on the f_M differs as the value of f_M itself.

Also, I wanted to comment on the timebase frequency.  The manual of the 9234 specify a minimum/maximum data rates when using an external timebase.  You need to make sure that the timebase frequency is at least 256*minimum data rate.  The reason I said to specify 12.8 MHz is because you can obtain a 50 kHz data rate by dividing down according to the formula in the manual.

f_S = (f_M / 256)/n, where is any integer from 1 to 31.

I hope this helps!

[mdelsol]

Hi Jesus,

Thanks for your try and effort but I think that you didn’t understand at all the problem. I know how to synchronize DSA devices, I did it many times on PXI systems. Problem is the error that appears in this specific case, explained on firs post. I can’t send you an example because I’m on holidays and I don’t have LabView on this PC.

On the topic says synchronization different rate, so the problem is synchronizing 2 DSA (NI9237 & NI9234) on cDAQ-9178 using 2 tasks, different rate and trying to share the sample clock time base of any of the devices. According to all the manuals and specifications should be possible to do such thing, but I tried all the different possible ways to do it but always appears the error that I mentioned on my first post.

If you want to reproduce the problem, I don’t recommend using simulated devices, as triggering and timings do not work.

When I came back from holidays I’ll post an example, but trying to share the sample clock time base between the tasks always appears the error, so it’s very easy to reproduce. Any way I recommend you to read my first post again to see if you understand better the situation.

Regards,

Marc.

[mdelsol]

Hi,

Related examples and commentaries can be found on topic:

CAR ID 208056 (SampleClockTimebase property incorrectly supported by cDAQ)

Regards,

Marc.