Using the rotational rulers

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Technician
TwoWaves
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Using the rotational rulers

Post by Technician »

I would like to use the scope and let the scope calculate the number of degrees of crankshaft rotation mathematically without me manually counting the scope wave forms teeth. I have used the rotation rulers and can adjust them from one to four to measure up to 720 degrees, however if possible I'd like to use the software to calculate any given number of degrees of rotation, is this possible with the scope software as I have not found any written material on it to date!

Thanks

speck
TwoWaves
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Re: Using the rotational rulers

Post by speck »

Hi Technician, once you have placed the rotational rulers you only need to move one of the rulers in the left
hand corner and the degrees will show up in the top box. hope that's what you wanted to know.

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Autonerdz
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Re: Using the rotational rulers

Post by Autonerdz »

What Speck said.

Keep min mind though that, these measurements will be ball park figures and not as precise as you may need at times. When using these rulers, all the degrees are evenly spaced. Of course, that is not what is happening in reality as the speed of the engine is always varying.

speck
TwoWaves
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Re: Using the rotational rulers

Post by speck »

Of course these measurements are not 100% since your 720* are measured in a straight line, which is wrong to start off with. Has more or less nothing to do with the speed of the engine. Degrees a spaced out in a circle and not in a straight line. Hope that sounds logical.

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Autonerdz
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Re: Using the rotational rulers

Post by Autonerdz »

Lost me there, Speck.

It has everything to do with the speed of the engine. The degrees get closer together and farther apart as the engine speed varies. Each cylinder firing is an acceleration.

speck
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Re: Using the rotational rulers

Post by speck »

Hi Tom
The degrees are always the same, they do not get closer or farther apart. They appear slower or faster but
the are always at the same spot. The scope shows us a straight line(with no curves or radius) and that is why
you can't plot 360* accurate on a straight line. Although it is pretty close.
,

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TwoWaves
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Re: Using the rotational rulers

Post by Technician »

Thanks guys for your valuable feedback, which is very much appreciated. I have completed some engine testing using the WPS500x, and measured the crankshaft, camshaft and fuel injection event. As this is a brand new area of thinking to me I was wondering what the relationship between the WPS500x pressure wave would show in relation to the manufacturers valve timing diagrams. Using the engine example I created with the WPS500x, I have used the rotation rulers and used a ruler from the left margin to measure the number of degrees as Speck advised. What I have learned to date using the zoom facility on the scope is that it is near impossible if not impossible to accurately determine where the exhaust valve(s) and inlet valve(s) actually start to open and close in the valve timing cycle. The exhaust expansion chamber looks to have the same depth as the intake chamber, and I understand the variations in pressure acting through the valve(s) during the exhaust gas being expelled, and the intake charge being drawn in through the intake valves, thus the ripples effects there being caused by the variations in pressure as the valves are opening and gas flow is occurring. The valve overlap is also very difficult to establish even when the trace is expanded, and I feel there is a fine line when expanding the pressure wave form as the detail can be soon lost and then the closing and opening of the valves during the overlap period is lost! I can see and understand this WPS500x is excellent for visually comparing each cylinder to find faults in valve timing and engine valve mechanisms, but I have a lot more learning to do to date.

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Autonerdz
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Re: Using the rotational rulers

Post by Autonerdz »

Speck,

I think you are missing the point. Maybe I was not clear enough. Imagine a crank sensor. Each rotation is 360 degrees. Graph the frequency of a high resolution CKP and see what you get. Frequency changes and you can see each individual cylinder firing acceleration in the frequency graph. As frequency (speed) increases, there is more movement and therefore more degrees of movement in a given time. The degrees are closer together as the speed increases and farther apart as the speed decreases across the waveform capture. There are still 360 degrees but they are not evenly spaced. In the same given time measurement, you will have more degrees of movement in one section than you will measuring in in another.

The rotational rulers do not take any of this into account so there will be measurement errors. The rotational rulers would only be precisely accurate if the crankshaft was turning at a steady speed and that never happens in the real world.

This is an important concept to grasp is you intend to make accurate measurements.

speck
TwoWaves
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Re: Using the rotational rulers

Post by speck »

Tom,
Sorry mistake on my part. Forgot for a moment that the scope measures voltage over time.

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TwoWaves
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Re: Using the rotational rulers

Post by Technician »

Autonerdz wrote:
Sat Nov 24, 2018 5:05 am
Speck,

I think you are missing the point. Maybe I was not clear enough. Imagine a crank sensor. Each rotation is 360 degrees. Graph the frequency of a high resolution CKP and see what you get. Frequency changes and you can see each individual cylinder firing acceleration in the frequency graph. As frequency (speed) increases, there is more movement and therefore more degrees of movement in a given time. The degrees are closer together as the speed increases and farther apart as the speed decreases across the waveform capture. There are still 360 degrees but they are not evenly spaced. In the same given time measurement, you will have more degrees of movement in one section than you will measuring in in another.

The rotational rulers do not take any of this into account so there will be measurement errors. The rotational rulers would only be precisely accurate if the crankshaft was turning at a steady speed and that never happens in the real world.

This is an important concept to grasp is you intend to make accurate measurements.
Any chance of an example of the above to help understanding!

What interests me here is the part where you advise;

The degrees are closer together as the speed increases and farther apart as the speed decreases across the waveform capture

I accept this above, I see that because time changes, thus a crankshaft rotating at 8 times a second will appear to have teeth closer together than a crankshaft rotating at 4 times a second. But what I don't understand is this part;

There are still 360 degrees but they are not evenly spaced

I could accept that the teeth can appear to be spaced unevenly when viewing on a scope at some measured crankshaft rotational speed, however, the flywheels physical teeth are fixed at approximately 6 degrees and are not physically variable! The dynamic operation of the crankshaft through the 720 degrees has a big influence I think on what the scope will present, as pointed out above through a time period!

Is this a case of a persons individual perception of what one thinks they are seeing?

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