Hello group,
I wish to analyze the current waveform through the my stepper's windings.
Reason: uneven steps -
. As you can see, the application runs fine, the stepper steps, forwards, reverse, accelerates, etc; just the steps are uneven at low speed.
I will be receiving a Rigol DS1102E shortly. I have no experience with an oscilloscope, and am looking for guidance on viewing the current waveform on this stepper.
The stepper is driven by a Pololu A4988 motor driver with voltage regulators, configured at 16 uSteps/full step;
The stepper’s characteristics:
- Stepper rated voltage: 12V
- Stepper rated current: 0.33A
- Supply voltage: 18VDC, Li Ion battery, floating, ie not ground referenced
- L=48mH
- R=32.6ohms
- f= 10Hz - 100Hz (ie 10 to 100 full cycles of 16uSteps per full step per second)
My questions:
- I do not have a current probe, so plan to use a shunt resistor in series. The only technique I have found on the internet involves the use the A-B differential method illustrated here to measure voltage difference between two probes.
Is there another more appropriate or direct way to plot the current waveform using this scope?
- For shunt resistor value, my calcs so far if I am correct point to a 1 ohm resistance.
Does this look right?
Feel free to redirect me to any existing post dealing with this topic.
Thanks in advance for your responses!
Ron
Montreal
PS: I'm a bit of a noob with electronics, but I've been through the phasor representation for this setup.
This best you can do with 2 ch scope, shunt and floating DUT to see current and voltage. Main thing: Ground clips
must be connected together to same place. 1ohm is fairly large for shunt. I use special 0.1ohm non-inductive max. But in this case might not matter much since this is pretty civilized motor not near-short like brushless outrunners.
Cool, thanks for the reply MrW0lf!
I like your suggestion cause that way I'll get to see both voltage and current!
Thanx!
You can easily build a low-cost current probe that covers DC-200kHz range. Please look at the attached application note for details.
