Sensor, wiring or ring ?? (Digital)

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Re: Sensor, wiring or ring ?? (Digital)

Postby RYM6746 » Sat Apr 29, 2017 5:13 pm

How do two identical signals with two identical maths channels on two seperate front wheels give out a different result on the maths channel? Sensor has been changed due to no physical issue with the ring or air gap. If the wires had high resistance the normal operating voltage range would be different from one side to the other. This one has me confused :roll:
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Re: Sensor, wiring or ring ?? (Digital)

Postby Technician » Sat Apr 29, 2017 8:13 pm

Looking at your scope traces and Hz readings, are your wheels and tyres the same sizes across the axle?

Are your tyre pressures correct? Low profile tyres 'if fitted' can visually look OK by reference but once a tyre gauge is fitted the pressure can be very low and easily missed!

I ask this because your scope shows different Hz readings, I would have thought the Hz readings from each road wheel should be the same, unless something is happening with how the scope has been setup?
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Re: Sensor, wiring or ring ?? (Digital)

Postby Dcunning35 » Sat Apr 29, 2017 8:22 pm

Might be worth a read of steve smiths subaru case study , some great ideas using the optical kit . This does seem mechanical .
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Re: Sensor, wiring or ring ?? (Digital)

Postby RYM6746 » Sun Apr 30, 2017 12:33 am

It's the continuous drop outs on the suspect circuit that confuse me. If you were to ignore the drop outs and imagine a line between the drop outs then it would match the other side would it not? A different size tyre/incorrect pressure would just show a different speed with no drop outs? A ring issue would repeatedly show the same drop out on every revolution?
I'll try and upload a screen shot of the scan data which may help. As this fault is very intermittent and the car can be driven for days before a fault code is logged. You can also drive it for miles whilst monitoring wheel speed on scan data and everything looks good then randomly scan data will show either a spike in speed or almost no speed at all with glitches in it.
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Re: Sensor, wiring or ring ?? (Digital)

Postby RYM6746 » Mon May 01, 2017 7:25 pm

I realised at times the signal voltage would fall outside of the voltage I had written into the maths channel. So i fiddled with it and changed the colours and yet it STILL shows the drop outs on frequency on the graphed maths channel. I have left all the cursors in place on this capture to show you what I am measuring? If you swap the maths channels around the drop outs are always shown on channel B. HOW IS THE SOFTWARE WORKING OUT A DROP OF 398 Hz in that 9.4 ms (as measured between my rulers). I am not really seeing an average difference in Hz between the two channels (generally they seem pretty consistent). Where are you seeing this?
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Re: Sensor, wiring or ring ?? (Digital)

Postby Technician » Tue May 02, 2017 9:11 am

OK something to try. Each ABS sensor has three wires, connect your scope to the signal, ground and supply of each ABS sensor, get a driver and take the vehicle for a drive, ideally on the motorway, increase speed and adjust the settings on your scope accordingly while driving. Hopefully the vehicle will log the code. Look what happens to the supply/ground and signal of each ABS sensor, if you loose a signal or something changes, hopefully that point you in the right direction.

I had a similar problem years ago, only at very high road speed would a fault code be logged, which turned out to be a ABS sensor reading incorrectly, but only at high road speeds, at all other times there was no fault.
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Re: Sensor, wiring or ring ?? (Digital)

Postby Datchet Diagnostics » Tue May 02, 2017 10:20 pm

I have taken measurements between timeline 600 - 620 of your waveform where a frequency drop of about 50% is displayed by the math channel. This is not a true reflection of the wheel speed reported within that time frame neither does it indicate a vehicle / abs fault. A 50% instantaneous speed drop on a single wheel would certainly raise alarms within the module. A fault code and ABS light would be illuminated in the first instance, with such safety critical errors the module will not require a second repetition of such a drop.

I cannot offer an explanation other than a software issue. Have you tried reversing the channels or C or D ?
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Re: Sensor, wiring or ring ?? (Digital)

Postby Fat Freddy » Wed May 03, 2017 1:51 am

RYM6746 wrote:I realised at times the signal voltage would fall outside of the voltage I had written into the maths channel. So i fiddled with it and changed the colours and yet it STILL shows the drop outs on frequency on the graphed maths channel. I have left all the cursors in place on this capture to show you what I am measuring? If you swap the maths channels around the drop outs are always shown on channel B. HOW IS THE SOFTWARE WORKING OUT A DROP OF 398 Hz in that 9.4 ms (as measured between my rulers). I am not really seeing an average difference in Hz between the two channels (generally they seem pretty consistent). Where are you seeing this?


I'm glad you brought this up. Not the first time I've come across it. Previously I had thought it was me asking too much of the program/processor but that appears not the case as it appears another Maths channel can complete the task. It's something that definitely needs looking into. I've had the problem looking more misfires from the crank signal.

Long time bases seems to be a common factor. I hadn't tried to change maths channels before so that is some kind of break through.

Hopefully this can be fixed.

Cheers
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Re: Sensor, wiring or ring ?? (Digital)

Postby RYM6746 » Wed May 03, 2017 9:03 pm

I too hope it can be fixed. I actually thought those drop outs were hidden in the signal to begin with. It was only after spending half an hour analysing and measuring I realised that it was impossible. That is half an hour we don't get in a workshop environment. Also an unneeded sensor replacement. Admittedly I shouldn't of jumped the gun on the sensor but with a customer, boss and other work that all need a quick answer sometimes you have to pull the trigger. The car has gone at the moment and hasn't returned. I will keep you posted if they come back moaning. At least I can show them the scope capture and baffle them with science and let them know it's a bug in the software :wink:
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Re: Sensor, wiring or ring ?? (Digital)

Postby Dcunning35 » Wed May 03, 2017 11:30 pm

Dont beat yourself up , you made a call in a pressurised environment if your boss cant stand a wss , he needs to enable you to have time to test ,examine ,test , confirm it all takes time and sometimes we jump the gun hoping for the golden nugget !!.
Were human not infalable and id say the insight and learning curve wouldn't be found in any training course.
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