Reducing RF Interference

[stirling]

looking at the doc on the gecko site: quote: (Numbering is mine)

Method One:
1) Use a shielded 5-conductor cable for your motor to drive connection; 4 of the wires go to the motor leads
2) while the 5th goes to the motor case. Return the motor case wire to the drive’s power supply ground connection.
3) Ground the shield to your electronics control box at the control box end only, leaving it disconnected at the drive end.

in my setup the PS ground is connected to the case, so isn't 1) and 2) effectively terminated at the same place and is this ok?

Thanks

[Al_The_Man]

This is where the reference to ground and common often get confusing.
P.S. -ve or common terminal is often referred to as ground when it is not neccessarily at Earth ground potential.
Generally the motor frame ground conductor is taken back to a central Earth ground point.
As long as this applies, you should be OK.
Al.

[stirling]

Hi Al - thanks for your reply. Understood re: bad use of the G word, but in this case where it says ground I think it means ground. What I meant was, the doc seems to draw a distinction between the electronics control box and the drive’s power supply ground connection where certainly in my case, they're the same thing because I allways ground my chassis (and thought everyone else did too).

Anyway - moving on to the next methods in the gecko doc (sorry if I'm being a bit thick here)

Method Two: Install 20 to 50 uH chokes in series with each motor wire as close to the drive as is practical. The choke outputs go to the cable described above.

Does that include choking the 5th wire or just the actual 4 "power" wires?

Method Three: Install an L-C low pass filter (pi section) from your power supply to the drives. Make L 100uH; make C 1uF noninductive (multi layer ceramic capacitor). Use this in addition to both of the above.

Do I use ONE of these filters BEFORE the fan out to my three drives OR do I use THREE of these filters AFTER the fan out?

Thanks

Ian

[Al_The_Man]

No ground wire should have a choke in it.
I cannot really speak to the L-C filters, but the traditional method has often been to use one filter before fan out, although three certainly would not hurt.
You could always clarify it with Gecko themselves.
Al.

[stirling]

Thanks Al.

Maybe Mariss will pop by - if not I'll run it by gecko's support. JFYI I'm working on a piece of home brew using a (10 bit 5V) ADC and when just reading a stationary potentiometer with the cnc control box off the reading deviates by maybe 10mV (1 or 2 points) at the most. Soon as I fire up the cnc controler the readings deviate by around 75mV (around 15 points).

Ian