11-02-2006 01:20 PM
11-02-2006 01:31 PM
11-02-2006 01:46 PM
11-02-2006 03:54 PM
A few comments Re: most recent screenshot:
1. Re: Start Triggers for counter tasks.
The regular Start Trigger can only be used for counter output (pulse generation) tasks. For input (measurement) tasks, you would need to use an "Arm Start" trigger. Trouble is, you can only configure it using the DAQmx Trigger property node, like the ones where you set retriggerable = True. However, as far as I know, the "Arm Start" trigger (used for counter input tasks) can't be set as retriggerable. I don't think retriggering a finite acq could easily get you what you want anyway though. It doesn't leave you enough read time between finishing one acq and getting the next trigger. In sum, use the DAQmx Trigger property node to configure an "Arm Start" trigger with the appropriate inputs (signal source, active edge, etc.)
2. Since you have a unidirectional motion and you're only performing X1 quadrature decode anyway, I REALLY think you should get rid of the position measurement task entirely. Use your Freq task alone. The cumulative index of your freq samples IS the position. See earlier postings for more details...
3. I always do Period measurement rather than Freq. They seem conceptually equivalent, but I'm not certain that all the config calls are truly similar. In any event, you may need to change your DAQmx Timing call to use the "Implicit (Counter)" version rather than the "Sample Clock" version. I know that's what I'd need to do for a period measurement.
4. Not sure why you'd prefer a finite acq to a continuous acq. Early in the thread you talked about a graph looking "dumpy." Was that the main reason? If so, there are probably other ways to improve it.
-Kevin P.
11-02-2006 04:28 PM
11-09-2006 01:06 PM
06-24-2009 04:33 AM
Hi Milqman
I read some of your post regarding your project. I know it has been a while since 2006. However, I would like to get some ideas from it.
I would like to acquire a data of pressure and also angle from engine. Pressure sensor and angle encoder are used.
However, how to decide or how to design the VI so that the DAQmx will only require the data of pressure during the first trigger of angle encoder. Instead of that, how to know that the the angle encoder already 720 degree so that I would say it is already one cycle of pressure that I would like to acquire.
I would be appreciated if you or others could assist me.
Thanks.
-Fird-
06-25-2009 06:00 PM
Hi Fird,
I'm not sure that I completely understand your application- but from what it sounds like, I think you may be able to create separate DAQmx tasks for your angle and pressure and configure your triggers separately. It sounds like you just need a start trigger for your pressure measurement. Could you please explain in more detail what you mean when you say, "
Instead of that, how to know that the the angle encoder already 720 degree so that I would say it is already one cycle of pressure that I would like to acquire." ? Are you just wanting to trigger your acquisition when your encoder reaches 720?
Thanks in advance for the additional info!
06-25-2009 07:55 PM
Hi Anita.
Thanks for your response. Basically, I would like to acquire data of pressure using pressure sensor. At first, I would like to use angle encoder to determine the angle of the crank. However, as I'm using USB 6009, I wont be able to do Angular Encoder.
(Just to let you know, I'm having two USB 6009).
By taking some ideas from the attachment VI, I then design a similar VI to acquire the pressure signal while the angle encoder use as External Clock also as Trigger. Please refer to the picture below.
From an encoder, we will be having 3 main signal from A,B, and Z. For this VI, I'm using A as source of clock while Z as source of a trigger.
I'm not sure whether this way is correct or not.
I will test it tomorrow (as now at France is late night - 3am).
If you have any enquiries that could help me to try out this VI, please let me know.
Thanks.
-Fird-
06-26-2009 03:59 AM - edited 06-26-2009 03:59 AM