How to measure two frequency simultaniously in a PCI 6014

[balajikasthuri]

Hi I am measuring RPM of two gear drives by measuring the pulse/second(Measure frequency.vi). I have interlinked the gate of counter1 to the output of counter2. Similarly I have connected the gate of counter2 to output of counter1. to measure frequency.
This way in a cycle one counter acts as gate counter while the other counter counts and later the counters changes their role.But my problem is that I have to measure the two counters frequencies simultaniously.

I cannot do period measurement becasue I have several irregular pulse widths generated in each cycle.

I am currrently experimenting with mesure period(DAQ-STC).vi. I have the following doubts in this VI.

1)Can I replaced source configuration fr
om internal timebase to external PFI source signal.

2)If I replace my source signal from internal timebase to the pulse generated from my gear drive then would at the end of 1 sec (when the counter is disarmed due to change of trigger signal state and hence end of while loop) will the count attribute contain the count of my ttl edges?

3) Would this be a accurate method for measuring frequency simultanuiously without using two counters?

Thanks.

[rgharrison]

Hi balajkasthuri,

The best way to perform this is to use the frequency generator (freqout) of your 601x board. Your board only has 2 counters but it also has a frequency generator that doesn't use the counters. It is an output found on the freqout pin. You can choose to have a frequency of 10 MHz or 100 kHz divided by any integer between 1 and 16. This means you can create a pulse train of known frequency and known period and use that into the source or gate of your two counters depending on the frequency measurement method you are using.

For example, assuming your two signals are much faster than the freqout signal, you can apply the freqout signal to the gate of a counter and have your signal feed the source. The number of counts you get in 1 pulse
width of the gate (which is known since it is the frequency you generated) will determine the frequency of your signal.

Otherwise, if your signal is much slower than 20 MHz, you can simply use the 20 MHz as the source of the counters and perform a simple period measurement on your signal. You would then take the inverse of your period measurement.

Anyway, using the onboard frequency generator will give you the flexibility you need. I have linked below a useful tutorial describing the 3 typical frequency measurements. Hope that helps. Have a good day.

Making Accurate Frequency Measurements
http://zone.ni.com/devzone/conceptd.nsf/webmain/CD2C8AAED8FA59A486256C230078FE75?opendocument

Ron

[balajikasthuri]

Hi Ron,

Thankyou for your tips.I initially tried to use this method. But my source frequency is very small 8KHz. Sorry I forgot to mention this. However I solved this problem by generating a signal from my AO channel.

Thankyou very much.