Hello Steeve, sorry for the late reply

I have to a say a big thank you to Martyn, Gerry and the technical support team for this one.

One thing is for certain “Maths is cool”

- Maths is cool

The following forum, post has this covered

https://www.picotech.com/support/topic2 ... ml#p101421 but I will add a note to help here with the formula.

Assuming your signal is present on channel A, the formula required is

“sqrt(integral((A)^2)/T)”Using our Guided Test for an inductive Crankshaft Sensor (to obtain an example waveform) I have applied the above math channel to channel A in order to graph the RMS voltage of the AC Signal

- AC RMS Math channel

I am far from a mathematician but the additional information that “maths” can reveal using PicoScope is staggering.

Above we graph the RMS of the AC voltage and with a little help from the scaling feature, we can clearly see the increase in voltage relative to the position of the collar.

So how do we arrive at this graphed RMS value using the formula above?

First we need to “square” (A^2) the AC voltage which has the effect of inverting the negative portion of our waveform (Full Wave Rectification)

The "integral A" of the formula then adds all "areas" under the curve together, which creates a sloping line with an inclination increasing with time

Then we divide “A” by the sweep time across the screen "/T" to level the line calculated using the integral

Finally, the “Sqrt A” will calculate the square root of the above level line to reveal the RMS value

I hope the image below will help.

- Formula application

Gerry has indicated a number of advisories in his forum post too but to summarise

The start of the math channel can be ignored as the software math function is dividing by zero, hence the confusion and oscillations at the start of the math channel before it climbs to the calculated value of approx. 570 mV RMS

Where using a trigger, the pre-trigger should be set to 0%, (with the yellow trigger diamond positioned on the far left of the screen), and be greater than zero, so that Time is always positive, and the waveform is meaningful.

There needs to be enough cycles of the signal waveform, to allow the Math Channel waveform to converge on a single value. If using measurements, only rulers placed on the converged DC portion of the Math Channel will give correct measurement values.

The RMS Math Channel will not converge quickly enough when zooming in, unless you're zooming in near the start or you CAN zoom in vertically if you use all of the horizontal axis.

The y-axis scaling of a Math Channel is not automatically proportional to the input channel/channels being used, so you may need to adjust it to match the Input Channel scaling.

The psdata file containing the above math channel can be found below:

Thank you again support team, I hope this helps, take care…….Steve