removing high frequency noise

[andy257]

Hi All,

The speed control input on my DC motor controller is an analogue signal ranging from -10V to +10V. When i look at the waveform on a scope it is awfully noisy and contains some high frequency spikes.

Can anyone recommend a way to remove the noise/spikes? Its difficult to say what frequency the nosie is, my scope does not have any advanced features.

thanks

 

[cowboybob]

At first blush, from your description, I'd say look into "by-pass" capacitors. If properly sized (capacitance values), these will shunt all manner of AC noise to ground.

 

[Boncuk]

Don't interfere with a working system!

If the motor performs as expected don't change anything - just be happy!

Boncuk

 

[Mikebits]

The ground lead of your scope probe could be picking up what your seeing. Use of a very short ground lead on your probe is prudent in viewing switcher waveforms.

 

[dr pepper]

Depends how big your motor is, if its a small one, less than a couple of amps a 0.1u cap accross the terminals, and one from each terminal to the case of the motor will quieten things down.
The noise could be comming from the controller itself if its a switcher, if its an industrial controller then there probably isnt a lot to worry about as it probably has filters on the speed inputs anyway.
You could try robbing a low esr 1000u cap from a scrap pc power supply and put it across the dc input if its powered from a dc supply,

 

[andy257]

i am using a PID controller to set the speed of my motor. i think this noise is coming from the on board DAC of the PID controller.

If i have high frequency noise on a pwm signal can i still filter the HF out without affecting the shape of the waveform.