PicoScope 7 Automotive
Available for Windows, Mac, and Linux, the next evolution of our diagnostic scope software is now available.
Steve Smith wrote: ↑Mon Feb 07, 2022 10:48 amHello Andy and thank you for the post
A great place to start regarding common ground (shared ground) scopes and floating input scopes is here https://www.picoauto.com/library/traini ... ing-inputs
Coming back to your scenario of simultaneously measuring Hall Effect Cam and Inductive Crank signals with the awesome common ground 4423, you have a number of options depending on the style of inductive crank shaft sensor/circuit architecture
With an Inductive crank signal using PCM/vehicle ground
You can measure all these signals reference to chassis ground as we describe here https://www.picoauto.com/library/automo ... e-running/
With an Inductive crank signal using a floating architecture (no ground reference on the crankshaft sensor wiring)
Again, your can measure both sides of the crank sensor wiring using channels A and B (if required) as we describe here https://www.picoauto.com/library/automo ... g-running/
This is only necessary if you wish to know the true amplitude of the crankshaft sensor signal. (i.e., if this is important to the measurement)
If amplitude is relevant, you can use the built-in math channel A-B to reveal (See below)
Image 1.png
In the majority of cases, you may only be carrying out a correlation measurement (between Cam and Crank) and therefore just measuring one side of the floating crank sensor (referenced to chassis ground) is fine. Remember to measure the "Main" crank signal and not the "Sub" return floating signal as below (PicoScope 6 image used but refer to waveform structure only)
Image 2.png
Regarding inductive crank signals, you may wish to measure DC coupled rather than AC coupled if you are focused upon crossing points and bias voltages as these will be changed when AC coupled. (They will be centered about 0 V)
A word to the wise about measuring inductive crankshaft sensors (either PCM ground referenced or floating)
There may be occasions when measuring such sensors, the engine may stall, run uneven, or set a DTC. This is down to the architecture of the PCM / Crank sensor circuit and in particular their sensitively to intrusion from a scope probe (even with 1 MΩ impedance)
In such a scenario (I remember a Mercedes Benz B class W245) a high impedance probe may be required https://www.picoauto.com/products/test- ... 00-mhz-bnc to measure the signal, or, if you need to determine amplitude, a differential probe will help here https://www.picoauto.com/products//elec ... e-x20-x200 where you can measure across the crank sensor and capture the differential voltage on a single channel of your scope
I hope the above information helps and please feedback for any clarification
Take care……Steve