Voltage spikes

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xj12c
Newbie
Posts: 2
Joined: Wed Oct 03, 2012 8:55 am

Voltage spikes

Post by xj12c » Wed Oct 03, 2012 9:20 am

Hello. I have just started using my Picoscope and have made some messurements on lamda and AFM. I know that my voltage on the lamda is wrong since i used battery ground, bur my question is why all the Voltage spikes appear. Is it the car or the way is do the test?
Se picture[img]C:\Documents%20and%20Settings\nn\My%20Documents\My%20Pictures\lambda-afm.JPG[/img]

Martyn
Pico Staff Member
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Posts: 259
Joined: Thu Aug 11, 2011 7:43 am
Location: Cambridgeshire

Re: Voltage spikes

Post by Martyn » Wed Oct 03, 2012 10:08 am

Unfortunately we can't see your picture as your link is your local one.

When you type in the post a reply box there is a section below that will allow you to upload an attachment. So please upload the jpg or even better the psdata file for the capture "File->SaveCurrentWaveformAs"
Martyn
Technical Support Manager

Alan
Pico Staff Member
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Joined: Thu May 25, 2006 8:02 am

Re: Voltage spikes

Post by Alan » Wed Oct 03, 2012 10:25 am

Without seeing the images, my guess is that the noise is normal. The engine bay is an electrically noisy environment, within wiring looms there are wires with small signals (such as lambda) running next to other wires with high voltage spikes (injectors / ignition etc). To keep costs down there is no electrical screening in a wiring loom so crosstalk occurs (ie one wire picks up some signal from another).

As our test leads are properly screened from end to end it is unlikely that the leads are picking up noise so its probable that what you are seeing on the screen is actually whats happening in the wire.

Inside the ECU each input signal is filtered to remove such noise, fortunately PicoScope allows you to add filters so you can also remove such noise - the drop down arrow symbols next to each channel brings up the controls for this. For the lambda try a filter of about 100Hz to start.

Many people like to see both the filtered and unfiltered versions of a signal. So dont be afraid to add / remove the filter or change its value. The unfiltered version allows you to see whats really happening and check for drop outs & intermittent shorts etc. The filtered view is closer to what the ECU will see.

xj12c
Newbie
Posts: 2
Joined: Wed Oct 03, 2012 8:55 am

Re: Voltage spikes

Post by xj12c » Wed Oct 03, 2012 12:35 pm

Thanks Alan! I will try that next time.

Martyn: I saw the tab you mentioned now. I will use that next time I post.

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