WPS 500X ground

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maniekdaniel
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Joined: Thu Nov 17, 2022 7:38 pm

WPS 500X ground

Post by maniekdaniel »

Hi. If I'm using a 4425A oscilloscope, how is the WPS 500X grounded to the vehicle if the ground cable doesn't go anywhere?

Steve Smith
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Joined: Sun Aug 25, 2013 7:22 am

Re: WPS 500X ground

Post by Steve Smith »

Hello and thank you for the post

The WPS 500X would not be grounded to the vehicle chassis when using a 4425A as we are not measuring pressure with reference to chassis ground.

Could I confirm the WPS500 is connected via a BNC to BNC test lead
https://www.picoauto.com/products/acces ... ed-bnc-5-m
I ask the question because I am not sure about the ground cable you mention.....
“if the ground cable doesn't go anywhere?”

The pressure transducer outputs a voltage in proportion to the applied pressure at the WPS500x Test Port
The internal battery of the WPS500x provides both the power supply and signal reference to the internal pressure transducer to ensure the following output
1
1
The same applies to BNC current clamps with the 4425A, where the internal battery of the clamp provides the power supply and signal reference to sensing circuit within, so as to ensure the correct output voltage in proportion to the detected magnetic field about a conductor when current is flowing (e.g. 100 mV/A)

I hope this helps, take care……Steve

maniekdaniel
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Posts: 8
Joined: Thu Nov 17, 2022 7:38 pm

Re: WPS 500X ground

Post by maniekdaniel »

Thank you for your reply, Steve. Yes, I use a Bnc-Bnc cable. Regarding the older Pico Automotive oscilloscope with common ground, if I connect the WPS 500X to one channel, and on the other channel I connect both test leads (plus and minus) to positive, will the WPS 500X work properly?

Steve Smith
Pico Staff Member
Pico Staff Member
Posts: 1586
Joined: Sun Aug 25, 2013 7:22 am

Re: WPS 500X ground

Post by Steve Smith »

Hello and thank you for the feedback

If you connect as you describe: “connect the WPS 500X to one channel, and on the other channel I connect both test leads (plus and minus) to positive” with a common ground scope (4823 for example) then the signal reference for the WPS500 is going to be raised to the value of your “positive” value.

Note, with this connection configuration, the entire measurement system is “floating” (assuming we are on a laptop powered by internal battery) as we are still not grounded to the vehicle chassis on any channel.

As to the effects on the WPS (in terms of signal) I would need to replicate this scenario which I can do tomorrow. Can I assume that your “positive value” is 12 V?

My gut feeling is the WPS will output the differential between the signal reference (your positive value) and the output voltage of the transducer relative to the pressure at the test port

I will feedback on the results ASAP

Take care…….Steve

Steve Smith
Pico Staff Member
Pico Staff Member
Posts: 1586
Joined: Sun Aug 25, 2013 7:22 am

Re: WPS 500X ground

Post by Steve Smith »

In the video below, I have our WPS500x connected to channel A of a 4823 common ground scope

For more information on common and floating ground scopes please see the following article
https://www.picoauto.com/library/traini ... ing-inputs

On channel B of the 4823, I have also connected a x1 test lead signal and ground wire to +12 V on an entirely floating measurement system (i.e. a laptop powered via the internal battery)

Referring to the image below, we have a common ground scope whereby the entire ground reference is raised to +12 V
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1
The image above is a 4423 but architecturally identical to the 4823 in terms of common ground

As we can see in the video, this connection scenario had zero effect on the displayed pressure values regardless of whether the ground reference was at Zero or +12 V



My main concern in such a configuration, if you now connect a test lead to channel C and reference to chassis ground, you have a short circuit via the scope as the BNC shells (typically referenced to chassis ground) are at + 12 V

With that said, the automotive common ground scopes are protected via rapid blow, auto-resettable fuses for each channel which offers you a level of protection should a “short” occur

Please also be aware that when the ground level is floating at +12 V, the body of the WPS500x is also at +12 V and the potential for a short circuit to the engine or bodywork is very high indeed

I hope this helps, take care…….Steve

maniekdaniel
Newbie
Posts: 8
Joined: Thu Nov 17, 2022 7:38 pm

Re: WPS 500X ground

Post by maniekdaniel »

Thank you very much Steve for the clarification. Regards

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