NI 9188 Configuration

[fra009]

Hi everyone, I'm a new user of VeriStand and I'm having a little problem with the acquisition with my NI 9188 chassis. I've tried to measure a TTL with a 9403 module, defining in VeriStand 1 kHz as target rate, but I encountered some issues acquiring a bad signal when TTL frequency exceeds 180 Hz: I noticed that the System Time is updating of 1ms every acquisition (and it should be right), instead the Absolute Time is updating of 4/6ms; have I missed something in the configuration of my DAQ? I've just inserted the DAQ in the System Explorer tree and also the digital module; I thought it should be configured as controller but when I do that VeriStand sends me an error during the deploy (I've attached the error file), so I'm only able to set my LocalHost as Controller. Does anyone have an idea of what am I missing?

Thank you very much.

Francesca

[Cavarval]

Hello Francesca,

The NI cDAQ-9188 cannot be the VeriStand controller because it is not an Embedded System, so it cannot run the VeriStand engine. The controller will remain the computer.

I am not really sure about the behavior you are seeing but I believe it may be related to Windows being the controller. Can you post the system definition so we can take a look at how the hardware is configured? Please notice that if Windows is the controller, we really have no way to ensure it will deterministically execute 1 ms loops (the default setting is 10 ms).

What I believe is happening is that Windows in your system is just unable to run faster than 4 to 6 ms, which is close to 180Hz. Essentially, every time the loop takes more than 5 ms, you will probably end up missing an edge. Is this what you are seeing? Can you tell us what your ultimate goal is? (count edges, calculate frequency, simply display the signal in a graph..)

Regards,

[fra009]

Hi Camillo,

Thank you for your answer. For now I'm only testing the hardware and learning how to configure VeriStand in order to create a software acquisition for motoring testing with NI 9188 chassis, and in particular I'm searching a method to acquire rpm signal with 9403 module. You're right, It seems that my computer can not achieve higher rates, so I had a text without the HW configured in the System Explorer, I acquired the Absolute Time and the System Time again and they both upgrade of 1 ms every acquisition, and so I thought that I was configuring something wrong in my System explorer (I attached the file, it has very simple settings).

Francesca

[Cavarval · Accepted solution]

Hello Francesca,

The code looks good so this is probably just the computer not being able to keep up. I see three options for you. From simplest to most complex method, you can:

1. Replace the NI 9403 with a module able to access the on-board counters from the cDAQ-9188 like the 9401 or 9402. This would allow you to perform a frequency measurement in VeriStand and sing a calculated channel to go from there to RPM would be quite easy.

2. Using LabVIEW instead of VeriStand: while the NI 9403 can only be used to perform single point acquisition in VeriStand, in LabVIEW, you can create a Hardware-Timed Digital Input Task, which will be able to keep up. In fact, you can configure each channel to acquire at up to 140 kS/s.

Refer to the Digital - Continuous Input.vi example in LabVIEW by going to Help » Find Examples... » Browse (according to Task) »Hardware Input and Output » DAQmx » Digital Input to find it. The example will acquire a digital waveform, but you can use the Waveform palette VIs to convert it to an Analog Waveform and perform a frequency measurement.

Is there a specific reason you want to use VeriStand for this project? Is it possible for you to use LabVIEW?

3. This would require some additional work, but if you pull 2., you can develop a Custom Device to integrate that functionality in VeriStand.

https://www.ni.com/docs/en-US/bundle/veristand/page/custom-device-build.html

That process is not trivial, but if there is a specific reason you want / need to use VeriStand, this would help you avoid getting an additional C Series module (if you don't have a suitable module for the first method already).

I hope the information is helpful for you. Please let me know if you have further questions and I will be glad to help!

Regards,