This guide, written by our expert Steve Smith, will show you how to leverage PicoScope’s built-in math channels to transform raw data into actionable insights. Why look at voltage or current when you can instantly view calculated parameters like resistance, power, RPM, and torque? This powerful feature allows you to solve complex diagnostic problems faster and more effectively, even on previously saved waveforms.
What are PicoScope Math Channels? #
Math channels are virtual channels in the PicoScope software that allow you to create custom formulas from your live or saved data. You can perform arithmetic operations, apply filters, and convert signals to display new, calculated waveforms. This turns your PicoScope into a diagnostic powerhouse, making complex math calculations simple and visual.
The application of Math channels:
1. Make sure that you have enough samples on the screen, ideally a minimum of 1 MS/s. PS7 defaults to 2 MS/s (above).
2. Make sure you have sufficient data on the screen containing the relevant information required, e.g. voltage fluctuations or several specific cycles/events.
3. Give PicoScope the time to fill the screen with data, do not stop the capture midway across the screen.
4. Make sure that the captured signal does not over-range at any point during the capture.
5. You may have to apply lowpass filtering to remove noise/spikes from the waveform. This will even out the math channel equal to the original signal.
Example of a typical waveform ideal for use with Math channels:
This waveform consists of the battery voltage and the starter motor current on a cranking engine during a relative compression test. It has sufficient samples, a complete screen/buffer of data with several compression events and with no over-ranging. It has a 1 kHz lowpass filter applied to Channels A and B in order to improve the results displayed by the math channels.
Math channels are found by opening the More menu and scrolling down to the Waveform Evaluation menu
Starting with the math channel A/B (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 (Ohm’s law in action).
Now, if we multiply Channel A by Channel B (voltage*current), we get Watts (power), where the peak electrical power occurs at peak compression, measuring approximately 1.28 kW.
Knowing the number of cylinders for this engine, four, we can determine the frequency of 2 x peak compression events based on peak current. These are evident between the time rulers.
A four-stroke, 4-cylinder engine will produce two compression events per engine revolution. If we know the frequency of these events, we multiply by 60 to obtain and graph RPM (cranking speed as indicated in the Frequency/RPM legend).
The formula for RPM is, in this scenario, 60/2*freq(B). Notice the excellent and stable cranking speed of approximately 280 RPM across the whole capture.
Finally, we can also obtain torque. Given that we know power and RPM, add in a constant of 95 (for Nm) and this is the formula: 9.5*(A*B)/(60/2*freq(B)).
The waveform below shows how peak torque occurs at peak compression, using Channel B – current as our reference.
We originally started with a simple capture with only voltage and current, but with the addition of some maths, now we also have resistance, power, speed and torque.
The .psdata file below contains all the waveforms and math channels used in this session. Remember to activate the lowpass filter for Channels A and B.