differential frequency measurement

[sgergo]

Hi to all,

and greetings to everybody! I would like to know more about differential frequency measurement and I'd be grateful if someone would point me in the right direction (theory, links, circuits, books etc.) Unfortunately I can find pay-per-view articles only on this topic.

Thanks

 

[Hero999]

What do you want to do?

Measure the difference between two frequencies? There are many different ways to do that, it depends on what you're doing.

 

[sgergo]

I want to measure the frequency of an oscillator. The oscillator will change it's frequency over time (it is contacted with chemicals). I would like to measure these changes. As far as I know, there is the frequency counting method and I heard about this differential method. If I'm not mistaken it provides faster sample rates because it doesn't need 'long' counting intervals so I can have more frequency data per second.

I think it is based on mixing the signal with one with a reference frequency and measuring the beat frequency. But I reckon it is not that simple.

 

[Hero999]

What's the frequency?

How about using a much higher frequency oscillator and counting the number of pulses per cycle of the frequency you're measuring?

For example, if it' varies between 1Hz and 2Hz and you use a 10MHz oscillator, you can get a reading once or twice per second, depending on the frequency.

 

[crutschow]

Why do you need fast measurements?

Another fast method is to measure the interval of one cycle and calculate the frequency from that.

 

[Grossel]

Would both frequensis have same amplitude? Would both signals be sinusoidal?