Measuring RPM using edge-count with USB6008

[bob the blade]

Dear all

I would like some guidance regarding what is probably a very simple problem with someone who is familar with Labview and I'm sure given the time, I could solve it but time is not on my side as is often the case!

I wish to measure the RPM of a rotating flywheel using Labview 8.6, using an opto-reflective switch sensor together with a USB6008 interface card. As I understand it, the opto-sensor produces a square wave output which is then measured by the USB6008 interface using AI0. I should then use the edge counter to measure this square wave right? It is AI0 port that I use since that has counter capabilities right?

I've had a good search on the website and the examples but I'm not sure how I'd set up the VI to do this? Reading the help files, I think I need to reference that signal to some sample clock - how do I do that? Can anyone point me in the right direction? I apologise profusely for the lack of knowledge and understanding I have, I just realised that I have to use Labview so am not familiar with it and I'd really appreciate some help!

[Dennis_Knutson]

No, you do not connect the signal to AI0. That is analog input number 0 and is very different than the counter input. The counter input is PFI0 which is pin 29. And no, you do not need to have any sort of reference. It is a simple event counter that is triggered by a falling edge. Did you look at the manual?

[bob the blade]

Thanks for your reply and useful info! I've had a look at the manual just now and I didn't realise that it was PFI0! Had a technician at Uni help set up the system and he said nothing about it! Input high voltage of 2V means I will have to reduce the signal voltage from 15V... thanks again!