Micro Amps Clamp Study

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Micro Amps Clamp Study

Postby STC » Sun Sep 03, 2017 10:47 pm

A simple fault and cure - Not so sure I could say that without the Pico's 4 Channels as my tool of choice.

Long standing issues with this car, a 2008 520d BMW N47 Engine. All 4 Glow Plugs and the Pre Heat (Glow Plug) Module have recently been replaced with new parts from our Favourite Motor Factor ECP. Invoices / Returns notes / Refund Confirmations to hand so no worry about repercussions.

Battery fully charged I unplugged the relay and used a Power Probe III to light up the plugs one by one, the voltage dropped from 12.7 to ~ 9.5 -9.6 on each one. Time to move on.

Power supplies and Grounds scoped whilst loaded and again time to move on. No surprise as the Fault Description was Communication Fault between DDE & Glow Module. Same Code with the Glow Module removed from the car.

All plugged back in

I see this


I see only one way Communication on the LIN Wire, With the aid of Pico Serial Decoding Channel added.

Another Module arrives from ECP and it takes less then 5 minutes to condemn it.

Purchase a genuine part from BMW and hey presto - Fault code clears

Known Good Capture


Again with Serial Decoding added to the LIN line we can see an additional signal. More importantly with the MICRO AMP CLAMP we can see current going the other way confirming that the ECU is asking and the Glow Module is telling it to turn the light out and allow DPF Regeneration.

I noted that the Parts cannon had been fired at this. O2S1, Exhaust Gas Temp Sensor. 4 Glow Plugs, 2x ECP Glow Plug Modules, Had it Serviced in hope! Bought himself a diagnostic machine as a last resort having been let down, disheartened, abused by garages he put his faith and a lot of money in. I have one friend now :D :D :D :D

In the past I would have cut the wire and scoped both ends looking for activity and response. With the clamp it is less intrusive and quicker. So much so that I have bought another and now have 2. Worth every penny I paid.

A also threw a Genuine new exhaust pressure sensor at this purely because it read 36mB engine off, pipe off and would not adapt down to "0"- Ignition on. 5v Ref and Ground were text book. New Pressure sensor gave plausible values and could be verified as accurate using a Mityvac and Live Data.
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Re: Micro Amps Clamp Study

Postby steevegt » Fri Sep 15, 2017 1:28 am

Nice catch STC!

Using this clamp for communication analysis/diagnosis is most likely the greatest future use that this type of clamps will have.
At least for me, the clamp was only useful in practice to pinpoint what was the LIN bus module that was not responding.

The only drawback of this clamp is that it has a short frequency response. I had tried this clamp in a 500 KBaud CAN wires, and if I remember correctly you can see the current jump when someone talks on the network, but that may be the maxim this handles. I guess that for Flexray, this may not fit.

A Micro Amp Clamp, with 100 khz bandwidth or more, that will be something... No tool is ever perfect enough I guess :D
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Re: Micro Amps Clamp Study

Postby STC » Sun Sep 17, 2017 9:50 pm

Hi Steeve
I guess that for Flexray, this may not fit.


Let's not knock it till we have tried it. It may surprise us :)
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Re: Micro Amps Clamp Study

Postby STC » Mon Sep 18, 2017 11:34 pm

Hello again Steeve.

this clamp is that it has a short frequency response. I had tried this clamp in a 500 KBaud CAN wires, and if I remember correctly you can see the current jump when someone talks on the network, but that may be the maxim this handles.

My last reply was possibly not clear. I don't expect to see the LIN, CAN or Flexray Signal using the clamp. We have been able to do that for years with the Pico by probing the wire or connector.

What this seems to allow (not yet tested the clamp on HS CAN) is to establish the direction of the message to confirm bi directional activity.

As in the BMW example above, LIN activity was detected on the wire and it was my GUESS that the reply from the module should differ from the wake up shout of the DME - A Guess and no more !!

In the past I would have cut the wire and scoped both ends looking for activity, hoping the Module didn't wait for the shout before replying. Ripe for a Mis Diagnosis - Not a fully accurate process !!

With the aid of the clamp we can see if there is communication in one or both directions. Possibly still one or two more curved balls to come (some of us revel in them) but we are one step further than we were without this tool.

Even if it is a tad slow, will it really matter ??

As with all Amp Clamps, We are only confirming, along side the voltage signal that current is flowing, measuring how much work is being done. Is that worker breaking into a sweat at his station or huffing and puffing running in the opposite direction (to the pub) ?


I guess that for Flexray, this may not fit.


I think / hope it will give an indication of direction ? For sure there has to be enough current for it to sneak its way through a transistor / FET / OpAmp and into a Processor ?? If so then the clamp will make the blue line cross the "0" line showing direction.

That is all we can ask of the tool ??


I have yet to try it on a wideband 02 - Looking forward to that.
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Re: Micro Amps Clamp Study

Postby steevegt » Tue Sep 19, 2017 11:18 am

STC wrote:Hello again Steeve.

My last reply was possibly not clear. I don't expect to see the LIN, CAN or Flexray Signal using the clamp. We have been able to do that for years with the Pico by probing the wire or connector.

What this seems to allow (not yet tested the clamp on HS CAN) is to establish the direction of the message to confirm bi directional activity.

In the past I would have cut the wire and scoped both ends looking for activity, hoping the Module didn't wait for the shout before replying. Ripe for a Mis Diagnosis - Not a fully accurate process !!


Hello STC!

Exactly, direction, and with that who is talking. Something that a voltage measurement is unable to tell you. At least without breaking the wire, like you planned to. But like you said, you may be adding variables with that.

I can tell you, it does work in HS CAN.
can bus 1.PNG
HS CAN Voltage VS Micro Current Clamp


STC wrote:Even if it is a tad slow, will it really matter ??

As with all Amp Clamps, We are only confirming, along side the voltage signal that current is flowing, measuring how much work is being done. Is that worker breaking into a sweat at his station or huffing and puffing running in the opposite direction (to the pub) ?

I think / hope it will give an indication of direction ? For sure there has to be enough current for it to sneak its way through a transistor / FET / OpAmp and into a Processor ?? If so then the clamp will make the blue line cross the "0" line showing direction.

That is all we can ask of the tool ??


The speed is not a problem, I agree, unless the current event is so short in time, that the voltage produced by the clamp is so small that we are unable to separate it from noise.
We are making measurements with signal far more fast that what this clamp was made to read, I assume that in this case the clamp in somehow averaging the signal.

STC wrote:I have yet to try it on a wideband 02 - Looking forward to that.


I haven't try it also. If you do, please keep us posted with your findings!
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