Cannot choose ENABLE FILTER on PicoScope 6

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hellochipboi
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Cannot choose ENABLE FILTER on PicoScope 6

Post by hellochipboi »

Hi all,

I am trying to measure any voltage from my embedded card. I need to activate the option Enable Filter to adjust the Cutoff Frequency in Advanced Setting for Measurement but all the advanced options are deactivated. I attached the screen capture below.
May I know how to fix this problem ? Thank you so much in advance.
I am using the version 6.10.18.1052.

Regards,
Attachments
Screenshot 2021-02-16 161013.png

Gerry
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Re: Cannot choose ENABLE FILTER on PicoScope 6

Post by Gerry »

Hi hellochipboi,

In some of the older versions of PicoScope 6 there were some options greyed out in the Measurements that were planned but not implemented. So if it's greyed out, unfortunately, you can't use it.

That aside, the measurements applied to Channel A are of the raw data, so any software modifications such as software filtering would not affect the measurement. So, for instance, if the filter used for the Input Channel Options is a hardware filter, then you can use it (e.g. the Bandwidth Limiter in the 5000 series) as it will change the raw data.

However, you can also create a separate Channel to measure, by creating a Math Channel filter of Channel A, and then measure the DC offset of that. I've created an example below which filters Channel A (but also offsets it, so that you can clearly see that the Measurement is actually working on the Math Channel instead of the captured data).
Measurement of filtered Channel A.psdata
(537.53 KiB) Downloaded 20 times
Measurement of filtered Channel A.png

I would be curious though as to what changes you're expecting to see to the DC offset, by applying a filter.

Regards,

Gerry
Gerry
Technical Specialist

hellochipboi
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Re: Cannot choose ENABLE FILTER on PicoScope 6

Post by hellochipboi »

Hi Gerry,

Thanks for your reply. Actually, I would like to measure a constant voltage from a PWM channel. The problem is that the noise of the measure is too high compare to the setting of the probe that is 12 bits precision (the collected data had about 8-9 bits precision, calculated by stdev/average). My tutor advised that I could adjust the cut-off frequency to a higher value (e.g. 10 MHz) to reduce the ripple of the signal.
May I know if your LowpassFilter is similar to that cut-off frequency option ? And is there others ways to try to reduce the noise of measurement ?

Thank you in advance.

Regards,
Attachments
constant voltage.psdata
(858.51 KiB) Downloaded 18 times
Screenshot 2021-02-18 105913.png
Screenshot 2021-02-18 105913.png (18.45 KiB) Viewed 724 times

bennog
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Re: Cannot choose ENABLE FILTER on PicoScope 6

Post by bennog »

You can add a math channel with a low pass filter.
2021-02-18_14-11-57.png
Depending on the filter value you will get a straight line or a line with a slight wobble.
Benno

Gerry
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Re: Cannot choose ENABLE FILTER on PicoScope 6

Post by Gerry »

Hi hellochipboi,

If you're measuring a constant (steady state) PWM signal, then you can also capture many waveforms (using a Repeat Trigger) and then use Waveform Averaging to reduce the noise (see here: https://www.picotech.com/library/oscill ... -averaging). This, again, would be a Math Channel, so you can then select it in the Measurement Window.

Because noise is a wide bandwidth problem, you will also have components of noise in the bandwidth of the signal itself, which you can't filter without filtering the signal. Waveform averaging (if you have a large enough buffer to create enough waveforms) would be better for your PWM signal as it will reduce the variance in the signal itself without corrupt it, by rounding off the pulse edges (due to the reduction of its harmonics, if you set the filter cut-off too low).

Regards,

Gerry
Gerry
Technical Specialist

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