pico 4 voies

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jazzsrt8
Newbie
Posts: 1
Joined: Mon Feb 08, 2021 7:59 am

pico 4 voies

Post by jazzsrt8 »

Hello
I did the battery test with the 4-channel picoscope tool, and I would like to know how the software does to find all the measurements displayed , thanks

Steve Smith
Pico Staff Member
Pico Staff Member
Posts: 1025
Joined: Sun Aug 25, 2013 7:22 am

Re: pico 4 voies

Post by Steve Smith »

Hello and thank you for the post

The PicoDiagnostics (PD) Battery test results and calculations can be found here viewtopic.php?p=77701#p77701
The image at the end of the forum post above includes the formulas for a 2 channel measurement

When using 4 channels to carry out the Extended Drop tests we include 1 more formula
IMAGE 1A
IMAGE 1A
When we crank the engine, channel C (connected to Starter motor terminal 30 & ref to chassis ground) is subtracted from channel A to find the voltage drop (See Image 2)
IMAGE 2
IMAGE 2
Channel D voltage drop is automatically displayed by the scope as this is the voltage drop present in the starter motor ground line.

Be aware, whilst Image 2 has the correct measurement for channel C, the voltage drop on the positive line is high (924 mV) and this is most probably due to electrical noise.
The same could also be said for the volt drop displayed on the ground line (Channel D) @ 1 V

We need to tackle this issue with PicoDiagnostics and I will follow this up with the team ASAP as filtering is required and this is not possible using PD

We can however use PicoScope (PS) and apply the relevant filtering to obtain the typical average volt drop in both the positive and negative lines of the Starter motor (See image 4)
IMAGE 4
IMAGE 4
Note the voltage drop measurements are still too high
Typical values are 0.5 V positive line, 0.25 V ground line (total 0.75 V)

The best way to qualify the volt drop is during cranking and not at the point of inrush current (see image 5)
NB. Apply low pass filtering to remove the relevant noise
IMAGE 5
IMAGE 5
I hope this helps and please feedback for any clarification

Take care……Steve

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