External Scan Clock - acquire at fraction of external clock rate

[Phil_J]

"scan clock external - log scan at less than the external clock rate"

"I am using the Clock config vi to set the scan clock to external and connected to PFI0

PFI 0 is connected to a TTL level encoder, which is attached to the rotating shaft of a brake test dynamometer. The encoder provides 60 pulses per full rotation of the shaft. Thus I acquire 60 scans of the channels to the buffer for every turn of the shaft. So far, so good, this works fine.


However, I wish to use the same software on another dynamometer which is fitted with a different encoder. This encoder gives 1024 pulses per turn of the shaft. I do NOT want to acquire a scan for every pulse ( I don't want 1024 scans per turn of
thae shaft), I would prefer a 16th of this, say 64 scans per rotation. Can I use Clock config vi to set acquisition at some fraction of the external clock rate ?


I notice an example on your site describes setting the external channel clock to a fraction of the external clock, but I can't see anything similar for the scan clock."

[Russell]

Hello Phil,

The solution is to use one of the on-board counters to act as a frequency divider for your external clock. You set it up for "pulse train generation" and wire your clock to the source of the counter. I have attached an example program that will do this part. Then combine this with one of the external clock analog input examples and you're in business!

I hope this helps!

Russell
Applications Engineer
National Instruments
http://www.ni.com/support

[Phil_J]

Hi Russell,
Thanks for this suggestion, I will try it out at the first opportunity (within the next 48 hours).

I'll let you know how succesful it is. Max dynamometer speed is 2500rpm (i.e. (2500/60)x1024 pulses per sec from the encoder). So I guess the only issue will be whether the counter cope with 43KHz.

Many thanks

best regards

Phil

[Russell]

Actually, the source of the STC counter can take up to 20 MHz!

--Russell