Test and Measurement Forum


Post any questions you may have about our current range of oscilloscopes


Postby Gena572 » Thu Nov 09, 2017 12:31 pm

I bought a 2202A Picoscope from you. How true is it measuring THD for example at a frequency of 1 kHz?
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Re: 2204A

Postby Gerry » Mon Nov 13, 2017 10:47 am

Hi Gena572,

The short answer to your question is not very true.

If the THD that you're measuring is also present in your measurement system, then you want to minimize the contribution that the measurement system adds to the total THD measurement. Our PicoScope 2204A has a Harmonic Distortion specification of '< –50 dB at 100 kHz, full-scale input, typical', or 0.3%. A general rule of thumb is that the measurement system should be at least 3 times as accurate as the system you are measuring. What this means in practice is that if you use the PicoScope 2204A you will only be able to measure, with any accuracy, THD at ≥ 0.9%, or -40dBc (i.e. 40dB less than the carrier reference, which will be your 1kHz sinewave).

The best PicoScope for measuring THD is the PicoScope 4262 which has a THD of -95dB relative to a -1 dB full scale input, which is -94dBc (i.e. relative to the signal), or 0.002%, and means that you can measure THD, accurately enough, down to 0.006%, or -84dBc.


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