Inj and Ign voltages drops

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Inj and Ign voltages drops

Postby acca on Wed Jun 12, 2019 11:59 pm

Hello
I have a question about Inj and ign voltages logging, as one can see in the picture, those voltages are not constant.
Is that normal please ?

image ign inj volt.PNG
image ign inj volt.PNG (53.14 KiB) Viewed 3018 times
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Re: Inj and Ign voltages drops

Postby SDean on Thu Jun 13, 2019 1:38 pm

Hi,

I wouldn't be concerned about the way that the data traces look, as these can be changed a large amount based on the sample rate of the channel.

This is my ignition voltages logged at 100hz when the engine is idling at ~1000rpm. The missing Cyl 4 is because the event happened between sampling points, if I logged the channel at a higher rate I would have most likely have gotten these captured.

Ign Voltages.PNG
Ign Voltages.PNG (17.22 KiB) Viewed 3003 times


This is the same data with differing filters applied.

Ign Voltages Filtered.PNG
Ign Voltages Filtered.PNG (14.35 KiB) Viewed 3003 times


I have filtered Cyl 1 to the equivalent of 1hz logging, Cyl 2 to 2Hz, Cyl 3 to 5Hx and Cyl 4 to 10Hz.
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Re: Inj and Ign voltages drops

Postby acca on Thu Jun 13, 2019 4:10 pm

Ok, so it's hidden by sample rate !
Thanks
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Re: Inj and Ign voltages drops

Postby David Ferguson on Fri Jun 14, 2019 1:39 am

Nyquist to the rescue.

https://whatis.techtarget.com/definitio ... st-Theorem

Basically if you want to make sure you capture the details of a signal that can change at frequency X, you have to sample at 2X the frequency.

The diagnostic voltages for Injectors and Ignitions can really only be used to determine if they seem to be stuck high or stuck low, as you would need to sample at 20khz in order to see signals to resolved to the nearest .1ms
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