solving noise issue using RC filter

[student1616]

Hi all,
i was doing some research on RC filter to be used with Mach3 to solve the noise problem.
till now i used AC and Dc servo systems.in AC servo system,iam facing lot of problem.imean estop and limitswitch triggered bcz of noise(i tried debounce function.went up to 3000.but no use).
i tried using shielded cables,grounding the machine but not use.
so after looking at below data,i think if we can place a proper,calculated low pass-RC filter between the BOB and LPT,it will solve the problem.
http://www.9w2bsr.com/2007/12/accomo...e-spindle.html
http://www.microstepping.com/sherline/2000cnc-5.stm

but i don't understand how to know ur cutoff frequency to calculate the required component values.
usually i configure mach to work at 35KHz(kernel speed).so shld i calculate the Rc near to this value?

i need some help and info here to solve my problem.
thanks and regards

[student1616]

need some desperate help here guys.

[mcarvey]

What size pullup resistor are you using on the estop/limit switches? Are you using shielded wire on all of the wires (especially motor ones) If you choose a small enough pullup resistor (lowish resistance, say .2-.5K ohm) you should be able to solve all of your estop/limit switch problems.

-Matt

[student1616]

i made my interface card using this circuit.
http://www.cnczone.com/forums/attach...9&d=1211686493
it worked well on output side.but iam always facing problem with inputs.
with this circuit,the inputs will be always either low or hi(they won't be floating)

so do you recommend this? or shld i change the interface type.

thanks for the response.

[PTtec]

be careful... a pulse of 35khz have the main frequency of 35khz but is a square wave so it will have harmonics(35*2---35*4---35*xxx), so a rc filter possibly, is not the best way to solve your problem. try use diferents cables for difrents signals, with shields!

[student1616]

thanks for the reply.
i don't know much abt this RC calculations.
even though we use lower frequencies,we might face the harmonic issue right?
as i tried all the stuff of shielded cables etc,i want to try RC method also.
i just wanted to know how tough it is? is it worth placing inputs side,as it is the point where iam facing the problem.
frequent emergencies and false limit sensing.

[PTtec]

to see how the square waves are composed visit:
http://en.wikipedia.org/wiki/Square_wave
here you see that (in ideal way) a square wave is composed by a adiction of very waves of sinusoidal type with freq multiple of the main frequency
so if you want yse filters you have to make several filters of pass band type each one with central frequency of the component that you want alow pass. Or else a low pass filter with cuter frequency of ('x'*Fsquare) and in my opinion 'x' must be at minimun 7, but i tink that for your aplication is not a good solution!!
to see about low pass filters see:
http://en.wikipedia.org/wiki/Low-pass_filter

[PTtec]

in my first reply i maked the sum with even harmonics... wrong are the odds!
visit the link for a simpler description of a square wave
http://www.fly.net/~ant/bl-synth/4.harmonics.html
bruno

[DaveDoesIT]

Originally Posted by student1616 i was doing some research on RC filter to be used with Mach3 to solve the noise problem.

Have you tried asking on the Mach3 groups?

http://www.machsupport.com/forum/index.php

http://groups.yahoo.com/group/mach1mach2cnc/messages

Dave

[neilw20]

While you are lazy with your shift key, that same attention to detail with earthing and shields also applies. now i've had that gripe...
Think of the CURRENT that passes through conductors. If a current can flow because something is terminated then voltage can be induced in that conductor.
Output wires will induce current to flow in other conductors.
The purpose of a shield is exactly that it is a shield.
If it is terminated at both ends, then current can be induced in it and it's shielded wiring.
There is not enough space here, but simply put -- GET RID OF INDUCED CURRENTS.

Learn proper wiring practices and understand why it is done a particular way.
Circuit board layouts suffer the same problems. Any loop can have current induced in it.

I have had to mix audio cables with cables running 800A pulsed and it can be done without any filters. UNDERSTAND INDUCTION. PROBLEM SOLVED.