I wanted to begin a new post on the power of maths.

There is so much that can be revealed using math channels applied to the raw data we have captured.

The real beauty of math channels is that they are applied post capture to existing saved files (that maybe years old) to reveal new information about past faults

Once again the message is…………..

For information how to access the math channel menu/wizard the following link will help https://www.picoauto.com/library/traini ... onus-class where we discuss the “Built-in” math channel

*A-B*With regards to the application of math channels:

1. Ensure you have enough samples on screen. (Ideally, 1 million samples minimum)

2. Ensure you have sufficient data on screen containing the relevant information required. This may be voltage fluctuations or a number of specific cycles/events

3. Allow PicoScope time to fill the screen with data, do not stop the capture midway across the screen.

4. Ensure your captured signal does not over range at any point during the capture

5. Low pass filtering of the original signal may be required to remove noise/spikes from the waveform. This will have the effect of “smoothing” the displayed math channel as it does the original signal

The following waveform is a typical example.

Here we have battery voltage and starter motor current of a cranking engine during a relative compression test (i.e. crank non start)

The waveform has sufficient samples, a complete screen/buffer of data with a number of compression events and does not over-range at any point.

A 1 kHz low pass filter was applied to channel A and B in order to improve the results displayed by the math channels

Starting with the math channel

**(Voltage divided by Current) we can display the circuit resistance during cranking. Note how the resistance decreases in proportion to the current flow through the starter motor during each compression event. (Ohms law in action)**

*A / B*If we now multiply channel A and B, Voltage x Current

**we obtain Watts (Power) where peak electrical power occurs at peak compression, measuring approx. 1.28 kW**

*(A x B)*Given we know the number of cylinders for this engine (4) we can determine the frequency of 2 x peak compression events based on peak current. (These are evident between the time rulers)

A 4 stroke, 4 cylinder engine will produce 2 x compression events per engine revolution, if we know the frequency of these events, we multiply by 60 to graph & obtain RPM (Cranking speed as indicated in the Frequency/RPM legend)

The formula for RPM in this scenario is

*60/2*freq(B)*Notice the excellent and stable cranking speed across the whole capture of approx. 280 RPM

Finally as if that wasn’t enough, given we know Power and RPM, add in a constant of 95 (for Nm) and we can obtain torque! Here is the formula

*9.5*(A*B)/(60/2*freq(B))*The above waveform reveals how peak torque occurs at peak compression, using channel B (current) as our reference.

As you can see, we originally started this capture with no more than voltage and current, but used maths to obtain Resistance, Power, Speed & Torque.

Please add any math channels you use during diagnosis to this post and rest assured I will add more as we move on together.

Please also find the psdata file below containing all the above waveforms and math channels.

Remember to activate the low pass filter for channels A and B.

I hope this helps, take care……Steve