Active Filter Design: Motor Controller Current Sensing
- From: "Mike" <mep0716@xxxxxxxxx>
- Date: 21 Jun 2005 12:08:27 -0700
I'm using a Hall Effect sensor (ACS704ELC) to measure the motor current
through an H-bridge. The FETs are being driven with an Intersil
HIP4081 FET driver. I am using PWM (20k Hz)to control the motor.
The Hall Effect sensor outputs a 2.5v DC signal at 0 Amps, and 2.5v
+133mV/A as current increases. My goal is to read the RMS motor
current using an ADC channel on my MCU. It is clear that I have to low
pass filter the signal first, but I am not sure how to decide on the
proper cut off frequency. Filtering the signal to a point where I can
sample/RMS it within the MCU (in a reasonable manner) is fine. I
understand that in order to recover all of the remaining (after
filtering) freq components, I need to sample at atleast twice the
bandwidth. But what dictates my passband, stop band (cuttoff),
passband attenuation? How do you figure out within what frequency
range the motor current be calculated from?
I am in the process of setting up a sweet FFT module on my scope which
will allow me to view the actual motor current (voltage output of hall
effect) in f-domain.
I'd appreciate any suggestions, thoughts on how I should go about
picking the proper filter parameters to meet my goal.
Thanks,
Mike
.
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