Mitsubishi Electric Melsec-Q172DCPU User Manual page 226

7 EMC DIRECTIVES
(4) Precautions relevant to the electrostatic discharge
There is a weak part to electrostatic discharge in the surface of the module.
Before touching the module, always touch grounded metal, etc. to discharge
static electricity from human body. Failure to do so may cause the module to fail
or malfunction.
Do not directly touch the module's conductive parts and electronic components.
Touching them could cause an operation failure or damage the module.
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