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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.
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