PicoScope 7 Automotive
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WPS500x
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Technician
- TwoWaves
- Posts: 708
- Joined: Thu Apr 24, 2014 8:32 pm
WPS500x
Hello, I have been collecting some waveforms using the WPS500x. I have limited information regarding the analysis of the waveform results, however having studied the waveforms a little, one thing seems to stand out at me at the moment that does not appear correct!
Referring to the capture I have included, the WPS500x is labelled on the right hand side vertical axis in PSI.
Referring to the waveform the 720 degrees of crankshaft rotation shows a cycle. If we now refer to the expansion and intake pockets I can use the rulers to measure the depths of each pocket for comparison purposes, however, each time I look at the vertical axis labelled PSI on the right hand side I can see the scale reading 0.0 PSI, but again referring to my capture the ruler is positioned at 0.0 PSI which shows horizontally across the top of the exhaust expansion pocket now where the exhaust valves are actually open.
At this position where the exhaust valves are open is not actually 0.0 PSI, but should be reflecting the actual back-pressure through the exhaust system!
I think the point I trying to bring across here is that the scaling of the vertical axis appears incorrect, the 0.0 PSI I'd of thought should be below where the exhaust valves open, showing at the lower side of the ripples rather than the top side.
Is there a way of scaling the vertical axis?
The other concern that seems to stand out at me is that 0.0 PSI is reflecting no pressure, however this is not so as the atmosphere is at 14.7 PSI, so the WPS500x I think is reading in gauge pressure rather than absolute pressure, if then indeed the WPS500x is calibrated in gauge readings does that mean that the user should subtract atmospheric pressure from the ruler legend when measuring results of the waveform?
Sorry just forgot to ask, is the WPS500x measuring differential pressure!
Thanks
Referring to the capture I have included, the WPS500x is labelled on the right hand side vertical axis in PSI.
Referring to the waveform the 720 degrees of crankshaft rotation shows a cycle. If we now refer to the expansion and intake pockets I can use the rulers to measure the depths of each pocket for comparison purposes, however, each time I look at the vertical axis labelled PSI on the right hand side I can see the scale reading 0.0 PSI, but again referring to my capture the ruler is positioned at 0.0 PSI which shows horizontally across the top of the exhaust expansion pocket now where the exhaust valves are actually open.
At this position where the exhaust valves are open is not actually 0.0 PSI, but should be reflecting the actual back-pressure through the exhaust system!
I think the point I trying to bring across here is that the scaling of the vertical axis appears incorrect, the 0.0 PSI I'd of thought should be below where the exhaust valves open, showing at the lower side of the ripples rather than the top side.
Is there a way of scaling the vertical axis?
The other concern that seems to stand out at me is that 0.0 PSI is reflecting no pressure, however this is not so as the atmosphere is at 14.7 PSI, so the WPS500x I think is reading in gauge pressure rather than absolute pressure, if then indeed the WPS500x is calibrated in gauge readings does that mean that the user should subtract atmospheric pressure from the ruler legend when measuring results of the waveform?
Sorry just forgot to ask, is the WPS500x measuring differential pressure!
Thanks
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Re: WPS500x
Hello,
WPS500x will output 0V at the atmospheric pressure,this is the reason for 0 Bar/Pa/PSI reading.
Why do you need to see 101 KPa when you make some measurements at the sea level and I read 96KPa at 550m?My mesurements will be usefull for you or other users without some small conversions?Why to substract some unknown value?(you don't know the exact location of user what uploaded the file(for altitude,atmospheric pressure in the day of capture...)) so use the gauge sensor .Also most of the automotive sensors will show 0 Bar/PSI at the atmospheric pressure(rail pressure sensor,brake pressure sensor for example),this is only a convention.
Best regards
WPS500x will output 0V at the atmospheric pressure,this is the reason for 0 Bar/Pa/PSI reading.
Why do you need to see 101 KPa when you make some measurements at the sea level and I read 96KPa at 550m?My mesurements will be usefull for you or other users without some small conversions?Why to substract some unknown value?(you don't know the exact location of user what uploaded the file(for altitude,atmospheric pressure in the day of capture...)) so use the gauge sensor .Also most of the automotive sensors will show 0 Bar/PSI at the atmospheric pressure(rail pressure sensor,brake pressure sensor for example),this is only a convention.
Best regards
Last edited by victor2k on Sun Jan 06, 2019 8:39 am, edited 1 time in total.
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Technician
- TwoWaves
- Posts: 708
- Joined: Thu Apr 24, 2014 8:32 pm
Re: WPS500x
Thanks Victor, I think I could do with some research material for the WPS500x. Referring back to my example waveform above, which I produced myself using a 3 cylinder twin OHC engine, the exhaust stroke I am paying attention to. The pressure in the exhaust system is atmospheric (static) when the engine is not running. When the engine is running, the pressure is then differential pressure, what I've not quite got my head round at the moment is what the two rulers results in the legend are telling me! What I think the results in the legend are telling me is, ruler 1 is the lower negative pressure, and ruler 2 is the upper positive pressure, and adding both together shows the difference, the difference then being between the negative intake manifold pressure and the positive pressure acting through the exhaust system (differential pressure).