Triggering Data Acquisition using CompactDAQ

[D Reck]

I am using an 8 slot CompactDAQ with a NI-9411 Digital TTL Input and a NI-9233 Analog Input. I want to measure vibration in rotating machinery. To measure vibration, I am using using a hall sensor connected to the 9411 and displacement sensors connected to the 9233.  There is a magnet in the shaft that pulses the hall sensor every revolution.

What I am interested in doing is triggering the data acquisition of the 9233 off of the digital input of the 9411.  That way, I can poll a set amount of displacement data every time the shaft makes a revolution and map the shaft's path during one revolution.  The problem that I am having is that I can not trigger the 9233 off of a digital singal. When I use DAQ Assistant, in the triggering menu, I can select digital edge for trigger type, but for trigger source it does not allow me to select any modules/channels.  I tried converting this to DAQMX code and changing it there, but it would only allow me to select other analog input devices instead of digital.  Anyone have any ideas?   Thanks

[NI-Bongo]

Hi D Reck,

To select your digital I/O module for triggering, you need to put the 9411 in slot 5 or 6 to share the trigger.  See this KnowledgeBase article on how to do this:

How Can I Trigger a NI 9233?
http://digital.ni.com/public.nsf/allkb/4859504F14AF68DB8625721100640F26?OpenDocument

You may then want to share the the 9233 sample clock to correlate your DI with your AI sample clock.

NI-DAQmx: Correlated Digital I/O with NI CompactDAQ and LabVIEW
http://zone.ni.com/devzone/cda/epd/p/id/5256

Here's a document that discusses cDAQ technology in detail.

CompactDAQ Under the Hood - Three Technologies That Drive USB Performance
http://zone.ni.com/devzone/cda/tut/p/id/3705

I hope this helps!

[D Reck]

That solved the problem,  Thank you very much.

Dan

[Gurdas]

Hello John,

I have a similar application need but with a different set of hardware.

My hardware is : NI-9233 mounted into NI-9162 + NI-6009 for analog and digital signals.

I am measuring RPM of a shaft off pulses from a magnetic probe connected to PFI0 counter on the 6009. My RPM measurement is good.

I am also able to configure and capture vibration data using my 9233.

Now, I need to capture vibration data for exactly one revolution and triggered by the pulse coming from the RPM probe. I know how to extract data for one revolution but am challenged by how to capture such that my first vibration data point is sync with RPM probe pulse. I need this because I will then have to find the phase of each data point from the RPM probe passby point.

A not very good idea I am considering: Write code which will wait for the counter on 6009 to reach a certain value and when that happens acquire one revolution data from the 9233 buffer. But this is bound to introduce code and OS lags.

1) Any ideas? Don't suggest any new NI hardware as I am short on funds and time!

2) If I somehow acquire a 9172 chassis, can I use my 6009 in slot 5 or 6 to achieve triggering?

[Neal M]

Hello Gurdas,

The chassis will not do you much good in this case because you are wanting to route your trigger off of your USB-6009, not from a cDAQ Digital I/O module.  The problem arises because of 3 facts:  The USB-6009 is not a cDAQ device and will not work with a cDAQ chassis, USB is a non-deterministic bus (meaning you cannot pass signals across it) and the 9233 does not have an external trig line.

As it appears you already know, we do have hardware that would allow you to do this easily (for example the solution presented in the previous posts), but because you do not have this option, we will have to try to rig a different method to do what you want.

The only way I can think of to trigger your input is to use the analog inputs on your USB-6009.  You can then configure the AI to be triggered off of the digital line you are already counting.  If you need the capabilities of the 9233, you could wire your signals to both the USB-6009 and the 9233 and then compare the first sample off of the triggered AI (from the USB-6009) to the signal you are measuring from the 9233.  You can then determine when the trigger happened in reference to your signal and take care of the rest programmatically.

One more option you have would be to use one of your AI channels on the 9233 to input your digital pulse and acquire continuously.  Because the 9233 samples synchronously, you could tell within one sample where the trigger happened (because you can look at your trigger signal) and throw out all of the data for all channels before that point.

These are the only options I could come up with, I hope it helps.

[preston_johnson]

The best tools we have for this application is the Sound and Vibration Measurement Suite.  The tools provide LabVIEW will the rotating machinery analysis and displays such as orbit plots, bode plots, revolution based plots, and so forth.  With these tools, you would sample the speed pulse signal on an analog input, and use the tachometer function to calculate speed, the resampling function to organize the data on a per revolution basis, and the track magnitude and phase to monitor specific vibration sources such as out of balance, gear mesh, and so on. 

Take a look at

http://www.ni.com/soundandvibration/

http://zone.ni.com/devzone/cda/tut/p/id/6511

http://zone.ni.com/devzone/cda/tut/p/id/6107

Let us know what questions you have

[Gurdas]

Dear Neal,

Thanks for the input. Of your ideas, the last is most appealing - that is, I send the RPM signal to my 9233. I am going to give this a shot and revert with results in a few days.

Dear Preston,

I will give the S&V toolkit a look. I had access to a old version (2.0) but on a cursory glance could not locate the tacho and resampling functions you mentioned. We have been putting LV to task on some of our flagship products, most of which deal with Noise and Vibration. Our tyre noise simulation software, SilentRoll, GUI is fully LV.

Regards,

[preston_johnson]

The functions I am referring to are part of the order analysis tools.  Prior to our creation of the Sound and Vibration Measurement Suite, we sold these as the order analysis toolkit. 

There is an upgrade from your older toolkit to the Sound and Vibration Measurement Suite.  You will see this in the upgrade advisor, http://ohm.ni.com/advisors/ua