Picoscope 4444 reference waveform

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simos
Newbie
Posts: 1
Joined: Sat Jul 10, 2021 9:49 pm

Picoscope 4444 reference waveform

Post by simos »

Hi,
I just received a new 4444 from a reseller and I am trying to test it.

a) With the 441 probe zeroed (130 μV rms at 10mV scale), measuring the square wave reference waveform shows a DC offset of 95mV at 5V scale. Should this be < 50mV (1% of full scale)?

b) Is there a procedure to test whether/when the instrument needs professional calibration?

Thank you in advance,

Gerry
PICO STAFF
PICO STAFF
Posts: 988
Joined: Mon Aug 11, 2014 11:14 am

Re: Picoscope 4444 reference waveform

Post by Gerry »

Hi simos,

We apologise for the delay in answering your post (there has been a lot of other work that needed attention).

So, in the event that you are still looking for an answer to your questions:

(a) The scale you're referring to is ±50mV, so Full-scale is 50mV - (-50mV) = 100mV, and therefore the DC accuracy is ±1% of 100mV ±500 µV, which means the Scope is within the spec (just!).

(b) Unfortunately, the only way to be sure would be to send it in for calibration. But for future reference, there may be something that you can do, once you have some calibration results.

You can wait for a long enough period of time over which your usage remains fairly constant and then send in the Scope for calibration and ask for the inclusion of the values "as found". That way you will know what the accuracy is immediately before calibration, as well as since it was previously calibrated, so you will have an idea of how far the Scope has drifted out of spec during that time period. If your usage is fairly similar over long periods of time then you can use the amount by which the accuracy has drifted, since the last calibration, to extrapolate how long it will take, approximately, for the Scope to drift out of spec. This will give you a reasonably accurate period for when you should be sending the Scope back in for re-calibration (we normally recommend a ball park figure of a year, but that is highly dependent upon how close the operation/storage of the Scope is to its specified limits, the frequency of operation, etc).

Regards,

Gerry
Gerry
Technical Specialist

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