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Author Topic: Encoder pull up resistors  (Read 6762 times)

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Offline comet

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Encoder pull up resistors
« on: February 17, 2009, 02:40:49 PM »
Hi,
  Does anyone have experience of using pull up resistors on encoders?
The story is:
 While "playing" with a G340 and a servo (heds 5500 encoder) I noticed I had erratic movement
with cables 12 foot long.
  I swapped each cable out and found that it was the 5volt feed line,and if I shortened it to below
4foot it would work fine,even though the main power and a-b channel (screened) were 12ft long.
 I then put a seperate psu to feed the encoder,this made no differance same problem.
  I remember reading somewhere about putting pullup resistors on long a-b cablles, would this work on
the 5v line? if so what sort of value and series or parallel? which end encoder or drive?
     Cheers

Offline Hood

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Re: Encoder pull up resistors
« Reply #1 on: February 17, 2009, 07:35:09 PM »
For your seperate power supply you are probably needing to connect the 0V of it to your drives.
 Might be worth looking at getting a line driver.
Hood
Re: Encoder pull up resistors
« Reply #2 on: February 17, 2009, 07:47:34 PM »
12 feet is mighty long for encoder cables, though you can get away with it if things are quiet.  The usual recommendation is no more than 6 feet, unless the encoders are differential output.  Are those cables shielded?  If not, they need to be.  If they are, are the shields properly grounded - that is, ONLY at the end opposite the encoders?

The fact that you can run long signal wires if the power supply is local suggests you're getting noise in the power into the encoders.  Have you tried putting capacitors on the power pins of the encoder?  Usually two caps two decades apart is helpful - 0.1 & 0.001uF generally works well.

Regards,
Ray L.
Regards,
Ray L.

Offline comet

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Re: Encoder pull up resistors
« Reply #3 on: February 18, 2009, 03:32:42 AM »
Ray,
  interesting stuff,I dont need to run the cables that long I was just experimenting I will try the
cap method and see if that works.
  regards
  Tony