This Question Was
Submitted by a Reader
concerning Problems with
a CPU
I am having problems at one customer site with this particular CPU
and I am wondering if it could be caused by ESD. The background: This
CPU controls the functions of an industrial glass washer. It sits in
a protected, air-conditioned, line control cabinet, with the temp control
set @ 80 degrees F. The air-conditioner filters are changed on a regular
basis and the cabinet is kept closed. The CPU is powered by a dedicated
Murr 24 DC power supply which receives 3 phase 480V.
What is happening is that during inclement weather, the CPU will either
just stop on its own, or will not reset the morning after a storm.This
customer also has another piece of our equipment with the same CPU setup,
and it does not experience the same problems. The CPU in question has
an internal RAM with battery to store the program, and a flash EPROM
to load it. The only way to get the machine on line is to replace the
CPU. The same flash EPROM is used to load the program, and the machine
runs.
When the line goes down again, we have re-installed the supposedly "bad"
CPU, loaded the program, and it runs ! We have changed the CPU 3 times,
the power supply, the back plane that attaches the CPU to the IN/OUT
cards, and the IN/OUT cards. Nothing seems to help.
The CPU has a plastic housing with an external terminal strip for +/-
24 VDC incoming power and a ground. There is no grounding for the plastic
housing, and no visible ESD protection on it that I can detect. I also
think the housing is homogenous which would make for a good conductor/
storage module for an electrostatic charge. Is there a way, or anafter-market
"kit" I can buy, to possibly drain any electrostatic energy
that might be stored in this device (maybe install a de-ionizer in the
cabinet to neutralize static charges ?). I have consulted Siemens and
they have never heard of any of their CPUs having this problem.
Thanks for the help.
Can you answer this question?
Click here to see the ESD Journal's
response, written by our Technical Editor, Jeremy Smallwood.
