Quote:
Originally Posted by Lee
I've decided to try and antistatic the obs, and myself, looking at antistatic mats/grounding and even esd shoes
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Hi Lee,
Based on the description you have provided, it will almost certainly be ESD phenomena.
In your instance, since you will have little control in being able to implement
countermeasures at the shielding or circuit level of your off-the-shelf gear,
the measures you outline of changing your shoes, clothes, mats, etc. in
the observatory would be the best approach.
Imagine if the metal part of the mount you touched had a yellow/green
wire attached to it that went to the protective earth.
When the discharge occurs, it has very high frequency components and as little as
2m of that cable will have an inductance of about 2000 ohms at 300MHz.
When the ESD pulse occurs, the real "ground" reference at that instance is the
metal part of the mount itself. It will quickly charge up to some fraction of the
original source voltage. The parasitic capacitance formed between
some metal parts of the mount and the ground on which it stands is likely to be
in the order of 26pF. In fact that capacitance formed in air is where the initial discharge
current will flow at 300MHz. By comparison it will take its sweet time to bleed down the
higher inductance path of our hypothetical green/yellow wire.
During some part of the discharge, it may make its way down I/O cables as a
common-mode voltage to some other piece of equipment and cause it to fail.
The classic ESD problem.
As you know, sometimes you don't even need to touch the conductive discharge point.
An arc will occur and the intensity of the electric field can be enough to disrupt
or damage a sensitive circuit.
Re-thinking the carpet and footwear is definitely the first thing to do.
Ground loops won't be the root culprit in this instance. If you have ever shuffled across
the carpet in slippers and touched the metal door knob on a wooden door and
felt and seen a spark, you can appreciate nothing much in the way of ground-loops
was occurring in that instance.
