RPM with usb 6000 and digital Input

[chili023]

Hello I want to measure the Frequency of a signal (0-5V) in a USB 6000.

Since it does not do frequenzy readings I have to write the code by myselfe.

I want to use the digital input and measure the time between two edges.

So far so good. but my calculated frequenzy jitters around the correct mean. I have differences of 33 Herz up and down.

Frequenzy to read 200 Hz. So 5 ms between two phases. Signal TTL (0-5)

Here a codeexample of my while loop.

[Dennis_Knutson]

You are probably having normal jitter when using software timed acquisition. A five msec variation is actually quite good with just using the Windows timer. Why don't you use an analog acquisition with multiple samples and use the built-in analysis routine for frequency measurement?

[chili023]

That's what I figured.
There is no way to use the internal clock of the usb 6000?

I did that and was not happy with the measurement time.

Thanks for the reply

[Dennis_Knutson]

You only have an internal clock for analog input. Upgrade your hardware to something that has an actual frequency counter if you are unhappy with the 6000. It's a poor choice for what you want to do.

[chili023]

Thanks. I will do that.
Recommendations? 2 counters would be preferable.