Voltage interference on WPS signal?

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Amechs
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Joined: Fri Jul 06, 2007 10:12 am
Location: Meath,Ireland

Voltage interference on WPS signal?

Post by Amechs » Mon Oct 18, 2010 5:32 pm

Good evening,
I am a bit confused about what's going on here and hope someone can help.

Pico 3000,software 6.4.90.0,Windows XP

The scope is set up,CHA on the battery terminals,crank the engine and the CHA signal is somehow having an influence on the CHC signal which is the WPS,until the engine starts.
Battery volts v pump pressure.gif
Disconnect the clips from the battery and the WPS reports correctly.

Use a current clamp instead of battery volts and the WPS reports correctly.
Cranking amps,pump pressure.gif
I tried routing the CHA and WPS leads as far away from each other as possible,no change.

I tried moving the channel connections around,no change.

Can anyone throw some light on what's happening here.

Thanks for looking.
amechs

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Carl Grotti
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Location: Missouri, USA

Re: Voltage interference on WPS signal?

Post by Carl Grotti » Wed Oct 20, 2010 2:54 am

I'm a bit confused too, Amech.

Why do you think fuel pressure is wrong at where you indicated? If anything, what stands out is how the pressure goes negative. Also, it appears to me that the pump quit running about half way during the duration of your cranking.

Whatever fuel system you have there is obviously not holding pressure. Of course we have no idea what you are working on. It might be normal for that vehicle, I don't know.

Why did you use engine cranking current in the second capture instead of using a low current probe on the fuel pump circuit?

Regards,

Carl

Amechs
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Location: Meath,Ireland

Re: Voltage interference on WPS signal?

Post by Amechs » Thu Oct 21, 2010 8:37 pm

Thanks Carl for your reply,
Carl Grotti wrote:
Why did you use engine cranking current in the second capture instead of using a low current probe on the fuel pump circuit?

Regards,

Carl
This is not a fuel pump but an engine driven oil pump.

What's odd about the first capture is the pressure appears to go to about 100psi at the very instant the engine starts to crank :?:

In this one,I inverted channel A and adjusted the scaling and both siganls are almost identical.Hope this makes my question a bit clearer.
Battery volts inverted v pump pressure.gif
This is really annoying me because I have other saved captures from only a few months ago,using battery volts and the WPS and they are fine.So what has changed?

Cheers.
amechs

ziko
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Location: St Neots

Re: Voltage interference on WPS signal?

Post by ziko » Fri Oct 22, 2010 2:28 pm

Hi I am not the automotive expert, however this looks like interference somehow. How are you physically connecting the sensors? How long are the cables? Could you take some pictures?
Ziko

Technical Specialist

Amechs
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Joined: Fri Jul 06, 2007 10:12 am
Location: Meath,Ireland

Re: Voltage interference on WPS signal?

Post by Amechs » Sun Oct 24, 2010 6:37 pm

Hi Ziko and thanks for the reply.

The scope is connected using TA000 BNC to 4mm banana plug on CHA and the BNC to BNC lead supplied with the WPS.

Thanks.
amechs

Richard Boyd
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Location: Garden City, KS USA
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Re: Voltage interference on WPS signal?

Post by Richard Boyd » Thu Oct 28, 2010 5:06 pm

Amechs,

Have you tried swapping out the BNC-4mm and BNC-BNC cables with other cables? Your getting a ground loop situation - hence the reason the problem goes away when using the current clamp.

Regards,

Richard Boyd
Crag Technologies, Inc
http://www.pc-oscilloscopes.com

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