rev counting

[Rainer Krafft]

dear NI users,
I am fairly new to the world of Lab View and currently try to tackle a probably fairly simple task:
Hardware:
Laptop with 6036E PCMCIA daq card
NI-SCC carrier with an Analog Input module and a strain gauge module

Software:
Lab View 7 Express

Task:
On a turnaround pulley I need to measure the radial force as a function of its rotational speed. The force measuring part is done, now I struggle with the rev counting. The Speed sensor supplies 6 pulses per revolution at 24V signal amplitude. Maximum speed is about 8000rpm. How do I get from there to a rotational speed?
Two ways I can imagine; 1)use the analog input module to scale the signal level down below 10V and the get a feedthroug module to feed this signal into a counter (I haven't got a clue which one of those many described) and finally do some functions in LabView.
2) take the 24V signal, build a simple voltage divider or Zener diode to reduce the signal level to below 10V and the carry on like above. Since the counters only count, how do I get from Time counting between signal edges to revs/minute?
Can you offer any Help ?

thanks in advance

[Setu]

Hi Rainer:

I am assuming the pulses are supplied as a nice square wave. Then, yes depending on your hardware module you will have to scale the signal down to a certain threashold of either 5 or 10 volts, perhaps using a voltage divider. I am not sure how this will affect the signal.

The analogue counter will count the number of pulses i believe, not time. So for the quickest solution you can check the counter value every 5 or 10 secs and convert it to RPM. Then clear the counter and repeat. You have to be careful of the time here. firstly it has to be constant, secondly the counter can overflow (this depends on your hardware resolution and max speed). So be aware of that.

I am not sure if this answers your question, but hope it helps.

Regards,
--
Setu.