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Frequency measurement precision

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Frequency measurement precision

Postby maxwatt » Thu Mar 08, 2018 8:32 am

Hi to all,

I'm a new happy picoscope 2204A owner, I'm just trying it on my new project to measure the frequency of my generated square waveform, but I see some difference from my generated frequency and picoscope measured frequency, so I need to know what is the precision of my picoscope frequency measurement, so to can finally understand what is the problem (a measurement error or a generation error, and in the second case trying to fix it).

I'm generating waveforms from about 200Hz to 1000Hz and the measured error is from 0.3Hz to 1Hz.

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Re: Frequency measurement precision

Postby Gerry » Fri Mar 09, 2018 11:02 am

Hi maxwatt,

The Time-Base accuracy is 100ppm which is 1 10,000th. So, if you are measuring a frequency of 200Hz the error due to the input channel measurement should be be 0.02Hz.

If you are generating your own square waveform at 200Hz, the 0.02Hz error due to the hardware PicoScope capture of the squarewave is outside the precision of the frequency value statistics display in PicoScope 6 (it would just show 200Hz) but you would see a deviation of up to 30mHz. So the 0.3Hz (30mHz) error you are seeing is due to your Square wave generator. The same is true for the 1kHz square wave, the error would be due to your generator.

If are you using the Signal Generator then you shouldn't be seeing an error or 300mHz. For the Signal Generator we state in our specifications that the accuracy (error) is the TimeBase accuracy (error) + the function generator resolution (which for the function Generator is <0.02Hz, typically 0.01Hz). So, for 200Hz, the error would typically be 0.02Hz + 0.01Hz = 30mHz or less, and for 1kHz the error would be 0.1Hz + 0.01Hz = 110mHz or less.


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Re: Frequency measurement precision

Postby bennog » Fri Mar 09, 2018 9:18 pm

There is also a dependency with the sample frequency you are using to measure the frequency.
if your sample rate is say 2.5ks/s then you will see an error of 0.4 Hz on a 1kHz signal.

If you set the sample rate to at least 1MS/s your accuracy will be higher.

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