Measuring of impulse voltage

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santander
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Measuring of impulse voltage

Post by santander »

Hello,

I am using Picoscope to investigate rise time and half time of voltage pulses in the microsecond range.

I played around with it for the first time yesterday and I love it! Thank you for a great product.

I would like to set up a measurement that could display the time from the pulse reaches 50 % of the peak level until it decays to the 50 % level again.

I can measure this manually with rulers, it would be great to have an automatic measurement for this

Is this something that I can set up easily?

Gerry
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Re: Measuring of impulse voltage

Post by Gerry »

Hi santander,

What you're describing is "High Pulse Width", which you can find if you go to 'Measurements->Add Measurement', and then select 'High Pulse Width', in the drop down list for 'select the type of measurement'. However, the "standard" automatic measurements can only display one value. So, if your captured data includes only one high half of a pulse, then the automatic measurement "High Pulse Width" will give you exactly what you need. If you have more than one high-half of the pulse captured, then the automatic measurement "High Pulse Width" will give you the average of that value for the displayed pulses. If you want each individual "High Pulse Width" measurements for multiple captured pulses, then you can use our "Deep Measure" feature to give you a Table of various measurement values for each pulse, including "High Pulse Width".

Regards,

Gerry
Gerry
Technical Specialist

santander
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Re: Measuring of impulse voltage

Post by santander »

Hello, thank you for your suggestion. I checked the High Pulse Width measurement, but apparently it only shows the time the pulse is above the average. How can it be adjusted to show time above a certain fraction of the peak value? For example time above 50% of the peak value?

Gerry
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Re: Measuring of impulse voltage

Post by Gerry »

Hi santander,

Sorry, I just assumed that you had a 50% duty cycle pulse. There may not be a straightforward answer to your question, but in any case, in order to answer your question correctly, I'd need to know exactly what the pulse looks like. So can you post a data file of it.

Regards,

Gerry
Gerry
Technical Specialist

santander
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Re: Measuring of impulse voltage

Post by santander »

Attached is a typical pulse.

This is an IEC lightning impulse pulse with rise time of less than 1,2 us and half time of about 50 us.

The objective of my measuring is to verify that the rise time and half time is according to the standard.
Attachments
Screenshot 2020-10-07 173315.png

Gerry
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Re: Measuring of impulse voltage

Post by Gerry »

Hi santander,

Unfortunately, there is no way to change the parameters used in the Pulse Width High measurement from average signal level to 50%, so the only other option for automation would be a Math Channel.

From your image, it appears that the top half of your Pulse approximates a Triangular waveform, which means that the Total duration can be calculated using the integral of the waveform (area under the waveform shape divided by 2 times the height (which can be found from the channel values divided by the normalized channel values). So, to get your pulse width high duration, we would need to remove the lower 50% of the waveform, which can be done using a level filter. So I created Math Channels for:
1/ Pulse duration measurement
2/ 50% Level filter (based upon the waveform height remaining constant)
3/ Pulse duration of the top 50% of the waveform (by combining the 2)
These are shown in the Image and data file below:
Pulse Duration calculation.png
Pulse duration calculation.psdata
(69.63 KiB) Downloaded 1 time

The Pulse duration math channels give the pulse duration as the maximum of the value over the period of the waveform (which you can get automatically by applying measurement of 'Maximum' to the math channel). However, the values are zero outside of pulse duration waveform (which prevents the measurement from being done) so, in order to have the Measurement of the maximum value displayed it has to be done 'between rulers', which you place at the start and end of the Math channel waveform.
The Math channel for the duration of the top 50% of the waveform requires that the waveform height doesn't change, because you need to enter the height divided by 2 and divided by 4 into the following places of the calculation:
(2*integral(((A+abs(A-h))/2)-q))/((((A+abs(A-h))/2)-q)/norm(((A+abs(A-h))/2)-q))
where h is half the pulse height, and q is a quarter of the pulse height

So far so good, (assuming your pulse height is fixed) however, for the Math channel that calculates the duration of the top 50% of the waveform, there seems to be some issue with displaying the values unless, after a single capture, one of the Timebase measurement rulers is moved slightly. I could have gone further to come up with a workaround (of not having to move the ruler), but I don't know if this is something that you can use (with the restrictions on how it works). So I have stopped at this point to establish if this actually benefits you at all, and if it would be applied to captures of a pulse waveform with a constant maximum level.

Regards,

Gerry
Gerry
Technical Specialist

Gerry
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Re: Measuring of impulse voltage

Post by Gerry »

Hi Santander,

Sorry, I didn't make it clear in my last post that I can get rid of the need to measure between rulers (which would otherwise defeat the purpose) and I may be able to get rid of the need to fix the half height value, but to work on this further I would need to know if the approximation to a triangle wave is useable (showstopper) and if the fixed height half value is useable (possible workaround, as mentioned). Also once you have a measurement value you can automate the process of generating a CSV file containing the measurement, by using Alarms and an Automation command in a batch file.

Regards,

Gerry
Gerry
Technical Specialist

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