Pulse Width Modulation Meter
Pulse Width Modulation Meter
(OP)
I would like to read the percentage of the PWM ON-time during the running of a Brushless DC Permanent Magnet motor that has a Star 3-phase configuration.
Is the wiring in the diagram below a viable way of achieving this? The resistance will be 1/2 that used for an identical voltmeter on the incoming power.
http://www.unicopter.com/PWM_Measure.gif
Thanks,
Dave
Is the wiring in the diagram below a viable way of achieving this? The resistance will be 1/2 that used for an identical voltmeter on the incoming power.
http://www.unicopter.com/PWM_Measure.gif
Thanks,
Dave





RE: Pulse Width Modulation Meter
PWM duty cycle usually varies over the cycle and is not easily measured with a meter. If the duty cycle remains constant, it can easily be measured with the Duty Cycle measurement function found in most modern DMMs.
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Pulse Width Modulation Meter
The desire is to have a reasonable idea of what the throttle setting is by reading a meter that is connected full-time.
Dave
RE: Pulse Width Modulation Meter
Keith Cress
kcress - http://www.flaminsystems.com
RE: Pulse Width Modulation Meter
Thanks for your comment and mentioning the capacitor.
Dave
RE: Pulse Width Modulation Meter
RE: Pulse Width Modulation Meter
RE: Pulse Width Modulation Meter
RE: Pulse Width Modulation Meter
As I see it, you're looking for a low pass filter, and that's what you have. By voltage divider (assuming the meter has infinite impedance):
Vmeter = Vin [j/(w*C)]/[R+j/(w*C)]
multiply numerator and denominator by (w*C)/j
Vmeter = Vin /[-j*w*CR+1]
|Vmeter| = |Vin|/sqrt(1 - w^R^2*C^2)
For radian frequencies w<< 1/(RC), then |Vmeter ~ Vin|
For radian frequencies w>> 1/(RC), then Vmeter ~ 0
You can calculate attenuation at frequency of interest using the forumla above and select R and C accordingly.
There are of course other ways to build a higher order low pass filter with sharper cutoff if your interested. Google "RC low pass filter"
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Pulse Width Modulation Meter
"There already is a capacitor in the circuit. I'm not sure where and extra one would go."
The capacitor was added to the linked diagram after itsmoked sugested adding it. My error, by not stating that the diagram had been changed.
Your information is now to be digested. Thanks
Dave
RE: Pulse Width Modulation Meter
Also please note correction
|Vmeter| = |Vin|/sqrt(1 - w^R^2*C^2)
should have been
|Vmeter| = |Vin|/sqrt(1 + w^2*R^2*C^2)
=====================================
Eng-tips forums: The best place on the web for engineering discussions.