PowerSTEP01: Electrical constant of the motor (ke): clarification need for ST documentation: "Measure the peak voltage ..": What to measure exactly: Vpeak-to-peak, Vpp/2, Vmax or ... ???

[PSesz.1]

In UM2022, Appendix C Motor electric constant (Ke) measurement written:

"Measure the peak to the frequency ratio" (by oscilloscope).

Our question: what voltage to measure EXACTLY ?:

Vpeak-to-peak, Vmax, Vmid, etc ??

I think it's fundamental to get the right result.

See attached picture coming from a Rigol scope user manual -to see what I mean:

Thanks in advance,

Br,

Peter

[Peter BENSCH · Accepted solution]

Welcome, @Péter Seszták​, to the community!

This is indeed a little irritating at first glance. The information from Rigol is not really helpful here, because it refers to the shape of a pulse, with no reference to a zero volt line. However, the output voltage of a stepper motor is a zero-balanced sinusoidal voltage.

But as you can see in UM2022, fig. 54, the peak voltage (marker 1, 2.526V) actually refers to the peak voltage of one half-wave, i.e. not to the peak-to-peak voltage (please pay attention: the zero point for the time measurement is marked by the small red triangle in the upper right corner).

Regards

/Peter

[PSesz.1]

Dear Peter,

First of all: thanks for your kind reply.

My opinion in short: may I advise: to clarify relavant part of UM2022.

Something like: "Measure the zero to peak voltage (Vpeak-to-peak /2) .. 

or make an additional signs to picture , e.g.:

m'I right ?

My opinion in more detail:

we are engineers ..., hate to make a guess work or read unclear documentation -we have enough other TODOs anyway.

(see: to figure out from aTektronix specific oscilloscope picture what was the intent of the writer.

IMHO better to use brand neutral figures and/or more clear explanations).

Regarding Rigol picture in my prev. message (I use 4 types of oscilloscopes: believe me -I know you know- display of every scope is different.): the only reason was to show it: there are a lot of types of voltage 'peaks'.

Thanks for your answer again,

Best Regards,

Peter

[Peter BENSCH]

Thank you for the kind comment!

However, I would also like to point out that the term "peak voltage" has been defined for many decades, see e.g. Peak Amplitude. But of course one can always improve documentation, so thanks again for your improvement hints.

Good luck!

If the problem is resolved, please mark this topic as answered by selecting Select as best. This will help other users find that answer faster.

/Peter

[PSesz.1]

Dear Peter,

seems like to be: one Peter of two Peters has a habit to own the last word 🙂

So, if documentation would have contained words "Peak amplitude" (not only term "peak voltage") I would not have asked the question.

As this is not the case I hope my comments is totally adequate and there is no need to excuse the inaccuracy of a third party.

Anyway, thanks again,

Have a nice day (or night) !

Peter