10-18-2010 12:30 PM
Hi I have a VI that read and write digital an analogical Signal at the same time triggered by the same signal
the digital signal came from 3 optical sensor this have a 9 ns of delay from when they are activate and when they send the TTL pulse to the DAQ
there is no problem when the speed of the object is less than 2m/s but when is a 4m/s and so the pulses are missed the triger activate properly but the pulse are not recorded
my daq is a PCIe 6351
12-02-2010 11:07 AM
Hi,
I have been checking on your issue and I´ve found some possible causes of this.
The first thing you have to do, is to calculate the amount of pulses you are trying to measure, if your hardware configuration sends to many pulses even your moving object is not going to fast the amount of pusles are excesive.
If this is the case, one possible solution could be to reconfigure your software to reduce the amount of pulses.
I will post the other possible problems on other replys because the amount of text is limited.
Luis Elias
12-02-2010 11:09 AM
There are some thing you have to take care or.
If you are using a digital port to measure pulses (like encoder pulses) there are some considerations you have to take care of. Here is a link in which you can review this: http://zone.ni.com/devzone/cda/tut/p/id/8087
Anyway if you are using the digital port to acquire the pulses you can use Correlated DIO, this gives you the opportunity to use an internal 10 MHz clock to measure your pulses.
It is important to notice that because you are using a to 10 MHz the pulse width resulted is a pulse of 100ns width, which implies that your with must be at least 2 times larger than this; however, it is better if is between 3 to 5 times larger.
Luis Elias
12-02-2010 11:10 AM
I will also add an example of how to measure an encoder train pulse with a digital port.
Here is teh example of how you can use a digital port to measure an encoder: http://zone.ni.com/devzone/cda/epd/p/id/5753
The only problem with this one is that it has only two signals at the time.
Luis Elias
12-02-2010 11:11 AM
However, if you are using a PCI 6351 gives you 4 counters. This might be probably the best way to measure those pulses.
Finally, I do not know if you are having this problem, It might be possible that you data processing is slower than your data acquisition and that is why you are missing some pulses. If this is the case, you might want to use a queue to storage the pulses and then process them at a slower rate.
Here is an example of FIFO on DAQ acquisition using Queues to avoid the data loosing: http://decibel.ni.com/content/docs/DOC-12057
Another thing is to use the internal LabVIEW examples. You can find then on the find examples section of your LabVIEW.
I hope this is helpful.
Luis Elias
12-02-2010 11:25 AM
@lfelilas wrote:
I will post the other possible problems on other replys because the amount of text is limited.
Luis Elias
What do you mean by the "amount of text is limited"?
What is causing your reply to be limited?
12-02-2010 11:39 AM
Sorry, I mean the text box of the forum does not accept more than 10 000 chars.
It has nothing to do with the answer, I just needed to post it in different replys
anyway I just found another example that might be helpful,
http://decibel.ni.com/content/docs/DOC-4170
Good Luck
Luis Elias
12-02-2010 11:47 AM
@lfelilas wrote:
Sorry, I mean the text box of the forum does not accept more than 10 000 chars.
Luis Elias
I'm sure it can handle far more than that. And 10,000 characters is going to average out to about 1500-2000 words which would be a very long reply. Your individual replies would have easily fit into one message.
12-02-2010 12:05 PM
I just relized what just happend, I forgot to use the Word paste that is why it sent me the 10 000 chars problem. My bad, It won't happend again.