reading abs sensors on porsche 996

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reading abs sensors on porsche 996

Postby porschekiduk » Sat Sep 20, 2014 2:09 pm

Hi All, I have set up my pico 4423, as per presets and cannot get any sign waves at all, whether i use digital or analogue settings.Channel A used.

Any help would be appreciated.

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Joined: Sat Sep 20, 2014 1:58 pm

Re: reading abs sensors on porsche 996

Postby Steve Smith » Mon Sep 22, 2014 10:15 am

Hi Chris, I suspect these sensors are “active wheel speed sensors” The test procedure for these style sensors ideally require the use of a milliamps clamp given their output varies only from 6 to 15 ma approximately. (0.9 V to 1.55 V)

Unfortunately the milliamps clamp is very expensive given the resolution required at such low outputs, however, one possibility would be to use the Pico 60amp clamp in 20 amp mode.

Here you would need to interrupt the circuit with break out leads and then wind the signal wire numerous times through the jaws of the current clamp so amplifying the signal.

Using the filtering of the scope software and the “resolution enhance” feature you will be able to detect the switching current.

Alternatively you can utilise the AC coupling feature of the scope to measure activity on the ABS sensor signal wire when the road wheel is rotating. This will expose the fluctuations present on the signal wire that will reveal some valuable signal content allowing you to confirm sensor output.

I have attached 2 x psdata files looking at active wheel speed sensors on a Jaguar supplied by Philip Harvey at Meadowside Garage. They show how the coupling features of the scope (AC/DC) improves the detection of the speed signal

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I hope this helps

Take care…….Steve
Steve Smith
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