Not constant sampling rate

[User002]

HI,

I'm trying to acquire data from 4 DI channels with cdaq 9172 and NI9425 with 100Hz sampling rate and write it with a time stamp into a text file. It sounds easy, but unfortunately I can't achieve the desired sampling rate; the time between two measurements is not equal and bigger then 10ms. I tried continuous 1 sample adjustment defining the task. Is there any other method for conversion of the binar data to string? Could that be the reason for bigger time consumption? Please help.

zolee

[AndreasStark]

Hi Zolee,

please export your MAX configuration and port here because I can't see your task properties, specifically timing.

Regards,

[User002]

Hi Andreas,

I made the measurement with both of this two configurations. The sampling rate was without change.

Thanks,

zolee

[AndreasStark]

Hi Zolee,

I need the following from you:

Go to MAX and 

- create a MAX Protocol under Datei >  Protokoll erstellen > technischer Support

- Export MAX settings from Datei > Export

Regards,

[User002]

Hi Andreas,

as attachment you will find the MAX configuration. The task which I use is Hopfenpruefstand.

Thanks,

zolee

[AndreasStark]

Hi zolee,

I tried your program with a simulated cDAQ and your task and it works ok (only 1 ms jitter).

Unfortunately the 9425 only supports software timing, so you will always have a large jitter. If you need hardware timing take a look at the NI 9423.

Regards,

[User002]

Hi Andreas,

thanks for your effort. I tried the same VI as an exe on another PC and the results are even worse. Jitter about 30-40ms. There must be a reason why I have such a long time between two samplings. In the specification of the NI 9425 they speak about 7us! Is there any special adjustment in the windows to change the priority of the LabView tasks?

Thanks.

zolee

[AndreasStark]

Hi zolee,

unfortunately you simply do have the wrong hardware for this job. You can only use software timing which means you are totally dependable on Windows. For precise timing you need hardware timing which is not supported by this module. This module is not only intended for cDAQ platform but for compact RIO platform as well where the module are read by a FPGA. The sampling time of this module is 7us, but you can only take advante of it using the FPGA.

You can set the priority of any task in Windows task manager by right-clicking the task.

Please contact our sales department for other hardware options: +49 89 7413130

Regards,