PicoScope: horizontal (x-axis) scaling scaling of a Reference signal relative to another waveform file's signal

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PeterScope
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PicoScope: horizontal (x-axis) scaling scaling of a Reference signal relative to another waveform file's signal

Post by PeterScope »

I am using "Reference" feature of PicoScope to import a crank signal from a file, to use it as a synch signal for another waveform that has crank signal. But the problem is that in one waveform, the RPM is 600 RPM, and in another waveform file the RPM is 650 RPM and signal is "shrunk" or "stretched" horizontally relative to "Reference" signal. I want to align two crank signals horizontally: stretch or shrink one of the signals. I found "delay" function that only shifts the signal horizontally, but I need to "stretch" or "shrink" one signal relative to another signal from another file.

Gerry
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Re: PicoScope: horizontal (x-axis) scaling scaling of a Reference signal relative to another waveform file's signal

Post by Gerry »

Hi PeterScope,

Unfortunately, shrinking or stretching a waveform along the Time Axis is more complicated than it sounds.

Basically, you can't just apply a simple function, you would have to re-sample the data.
This means that you would need to create new data values representing intermediate vertical points on the waveform you would get when relocating the old data values to either before the original Time positions (for shrinking) or after the original Time positions (for stretching). The new data values would have to be interpolated using the available functions in the application method, for constructing the interpolation algorithm (e.g. linear, sinx/x, etc) that is most suitable for the Waveform type. This is something that you could do using our Software Development Kit (SDK).

BTW, I'm not going to say it can't be done, in PicoScope (or PicoLog) Software, but I would say that it's highly unlikely as there doesn't appear to be anyway to relate specific sample values.

Regards,

Gerry
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Ben Martins
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Re: PicoScope: horizontal (x-axis) scaling scaling of a Reference signal relative to another waveform file's signal

Post by Ben Martins »

Hi PeterScope,

We often come up with this issue when looking at cam crank correlation because as you say, when comparing signals the engine speeds can be different between captures.

Rather than shrinking or stretching the waveform we use 2 viewports and then the phase rulers to map out the 0-720 degrees on the crankshaft of both the reference and the live capture. Providing the phase rulers are lined up on the same points of the two waveforms it's irrelevant of engine speed as you can now use the time rulers to measure in degrees.

In the image below I have the before capture from a vehicle where the timing is out which is in scope view 1. In scope 2 is the same capture but after the repair. I've added in the phase rulers to mark out the boundary for 0-720 and used a time ruler at 0 and 360 degrees to show the engine speed where you can see the difference.
Reference waveforms with phase rulers.png
Using the same principle we can see the difference in correlation between the camshaft and the crankshaft by using the time ruler on the same edge for the camshaft.
Reference waveforms with phase rulers timing.png
If you need more automotive help please take a look at the automotive forum - https://www.picoauto.com/support/.

Not quite the answer you were looking for but I hope this helps.

Ben

Gerry
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Re: PicoScope: horizontal (x-axis) scaling scaling of a Reference signal relative to another waveform file's signal

Post by Gerry »

Hi Ben,

Thanks for the alternative (I forgot to direct Peter to the Automotive site and you guys).

Regards,

Gerry
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Gerry
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Re: PicoScope: horizontal (x-axis) scaling scaling of a Reference signal relative to another waveform file's signal

Post by Gerry »

For users of non-Automotive PicoScopes...there IS a way to shrink or stretch a waveform along the time axis (while sacrificing a little waveform definition).

If there is enough interest then, when I find some more time, I will post the method here.

Regards,

Gerry
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bennog
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Re: PicoScope: horizontal (x-axis) scaling scaling of a Reference signal relative to another waveform file's signal

Post by bennog »

I need a reference waveform with a horizontal scale factor.
So we can align it with a AB encoder ramp up and ramp down.

Benno

Willem43
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Re: PicoScope: horizontal (x-axis) scaling scaling of a Reference signal relative to another waveform file's signal

Post by Willem43 »

Gerry wrote:
Wed Nov 08, 2023 8:46 pm
If there is enough interest then, when I find some more time, I will post the method here.
Yes, please do.

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