Re: help with g201 needed

Hi,

I have to make a comment here. Electrostatic discharge is NOT a
concern with opto-isolated inputs, particularly in the GXXX drives.

The opto diode has a 1K resistor in parallel with it and that
combination is in series with a 200 ohm resistor. The impedance is so
low as to make ESD damage impossible in any practical scenerio.

One of three things could have happened:

(1) Excessive forward or "on" current. When that has happened the 200
ohm resistor has fried. Not the case here.

(2) Excessive reverse voltage. LEDs have a reverse or breakdown
voltage of about 5 to 7 volts. Voltages in excess of that will
quickly destroy the LED.

(3) The part was flawed from the manufacturer and failed after a
period of time. That ocassionaly happens (<< 0.1%).

For this particular drive (1) was ruled out by inspection. Though
possible, (3) is unlikely; I have seen that only twice in over 10,000
opto-isolators used. That leaves (2) as the most likely cause, though
it remains undetermined.

About ESD in general:

Small-signal MOSFETs without intrinsic gate protection zeners are the
most sensitive and must be handled with care. Bipolar devices (like
LEDs) are insensitive to common ESD and require no special handling
in my experience. In between are unterminated CMOS logic inputs of
which I have seen less than a dozen damaged by ESD in the last 20
years.

Mariss

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> Al Schoepp wrote:
>
> > At 06:09 AM 20/01/2002 +0000, you wrote:
> > >Al Schoepp wrote:
> > >
> > > > Hi Alan,
> > > >
> > > > Since I got the info that it was the opto that failed and to
check my
> > > > wiring I've looked everything over and can see no problems.
I installed
> > > > the repaired 201 and it seems to be working great. I have no
idea why the
> > > > opto failed, maybe a small piece of swarf got in there and
shorted
> > > > something out? I'm happy that it's working now but would be
happier if I
> > > > new what caused the problem in the first place.
> > >
> > >More likely it was electro-static discharge. Sometimes, tiny
discharges
> > >that you can't feel at all will destroy components. Sometimes,
discharges
> > >that make you jump, are audible and even visible will have no
permanent
> > >effect. Especially, if you are connecting and disconnecting the
cable to
> > >the computer, and removing the computer for other purposes, it
is easy
> > >to walk into the room with a charge on your body and touch the
connector,
> > >zapping whatever is on the other end of the cable.
> > >
> > >Jon
> >
> > I should have thought of that, that is likely what happened. I'm
using the
> > machine in my carpeted apartment and there is quite a bit of
static.
>
> You might want to put a sheet of aluminum foil down on the bench,
and ground
> it to a wall outlet. Touch the aluminum first before touching any
other part
> of the machine (computer, drives, CNC machine).
>
> Jon