PCI-6143 - Tying inputs together

[walter-donovan]

Hi all. I am trying to build a system to measure analog position vs quad encoder angle plus RPM to chop the results into one rev plots. The analog part is no problem but for the digital I have no experience. What I have / propose is:

Analog meas uses quad encoder z pulse to start data capture then reads a fixed number of points.

At same time, digital meas must determine the RPM for a certain revolution. A pulse is wired to PFI0, Z pulse is wired to PFI1. I plan to trigger one freq reading each revolution using the Z pulse. So I think I need to also wire the A pulse or Z pulse (I think) to a counter input to be able to measure frequency. Is there any reason not to jump PFI0 or PFI1 to ctr0 or ctr1?

[Eric-E]

I am a bit unclear on the measurement. A bit of further clarification would be nice. I believe you're basically asking how to  find RPM from a counter. 

http://digital.ni.com/public.nsf/allkb/9844C0526ECF4152862576660079ADBB?OpenDocument

https://decibel.ni.com/content/docs/DOC-21562

http://forums.ni.com/t5/Counter-Timer/RPM-Measurement-using-Quadrature-Encoder-and-PXI-6602-counter/...

[walter-donovan]

Thanks. The 1st 2 links you reference are not applicable as the measurement must be synchronized with a very high speed analog measurement. The third is where I am right now - freq measurement with 1 counter.

The z pulse triggers the frequency readings, one each revolution. When this happens I want to to poll the A pulse (360 / revolution) and get the frequency from the distance between 2 edges. I am also using the A pulse to reference trigger the analog measurement so it is wired to PFI0. The only thing I am asking is, since I need to use this A pulse for 2 different tasks, can I jump between PFI0 and counter 0 so I can get frequency data as well as have a reference trigger?

Also do I wire to the ctr0 source or wire to the ctr0 gate? I think the gate is what to use and the source would be the onboard clock but I am not clear on this.

[Eric-E · Accepted solution]

I think I understand. So not only are we using the quadriture encoder to measure angular position, but we would also like to know angular speed. We would like the angular speed to be calculated just once each complete rotation by measuring the time between two rising edges of the A lead of the encoder (please correct me if this is not right).

For the frequency task, I think jumping the A line over to another PFI line and monitoring this line as a frequency input using a separate counter from the first task would be the way to go. 

[walter-donovan]

Thank you Eric. This would be a good solution except I am coding this in Labview and have gotten no help in that board on how to make it work. I ressurrected the thread once but now it is 9 pages back and no help. Not sure what is so eluding about the task that no one seems to have an answer. I am forced to abandon this type of measurement, build a frequency to voltage converter and measure analog voltage. This I can code wihout relying on help. Seems like my only option.

Thanks again.

[Eric-E]

I'm sorry that you're not getting much help online. You might try to start with some basic examples online which do similar things such as:

https://decibel.ni.com/content/docs/DOC-11954

[walter-donovan]

Thanks for the guidance Eric. I wasn't really aware of these other resources and will use them in the future. I thought my only options were these boards and the canned examples (which usually add insult to injury by showing a working method that is just far enough away from my application that I can never modify it and get it to work :). In any event I have had to order extra hardware, erase all the digital acq code and rewrite for analog (which is a place where I am more comfortable).