Back on December 13, 2009 Lionel Lhermitte (F6FCD) posted ...
Hi David and all,
Quick reminder about anti-static stuff. Your pad and hand-strap must NEVER
be connected directly to the ground.
Between those and the ground a resistor of 1 mega ohm must be inserted.
... and I reply posted ...
Actually David, your ESD dissipative mat *should* be connected directly to
ground. The 1 Meg resistor is contained somewhere within the ESD wrist
strap assembly.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Well I've since researched this subject (using industry proprietary sources)
and sure enough Lionel was correct about it being acceptable to have a 1M
resistor in series with the mat as well. Actually, I found that there are
two acceptable configurations, both of which include two 1M resistors. The
two configurations are presented pictorially below.
BTW, these 1M resistors are built into the ESD equipment so there's nothing
that a user needs to do other then plug the equipment together and use it.
What Lionel described in his post isn't something someone would be aware of
unless they took the time to measure the resistance between various points
in the circuit. Well at least I wasn't aware of it!
Personally, I wouldn't be too concerned about the 1M resistor in series with
the mat. By my math it is statistically insignificant. In contrast the 1M
resistor in series with your wrist strap is of life and death importance!
73,
Gary KI4GGX
K3 #2724
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1M 10%
+----/\/\/\------> Wrist Strap
|
|
| 1M 10%
+--------------+----/\/\/\------> ESD Mat
|
|
|
----- "Earth" i.e. third wire ground
---
-
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1M 10%
+----/\/\/\------> Wrist Strap
|
|
1M 10% |
+----/\/\/\----+----------------> ESD Mat
|
|
|
----- "Earth" i.e. third wire ground
---
-
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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