5.8 Safety Measures
5.8.1 Safety Measures
Precautions regarding system design
In certain applications, malfunction may occur for the following reasons:
•
Power on timing differences between the PLC system and input/output or mechanical power apparatus.
•
Response time lag when a momentary power drop occurs.
•
Abnormality in the PLC unit, external power supply, or other devices.
In order to prevent a malfunction resulting in system shutdown choose the adequate safety measures
listed in the following:
Interlock circuit
When a motor clockwise/counter-clockwise operation is controlled, provide an interlock circuit externally.
Emergency stop circuit
Provide an emergency stop circuit to the PLC externally to turn off the power supply of the output device.
Start up sequence
The PLC should be operated after all of the outside devices are energized. To keep this sequence, the
following measures are recommended:
•
Turn on the PLC with the mode selector set to the PROG. mode, and then switch to the RUN mode.
•
Program the PLC so as to disregard the inputs and outputs until the outside devices are energized.
Note) In case of stopping the operation of the PLC also, have the input/output devices turned off after the
PLC has stopped operating.
Grounding
When installing the PLC next to devices that generate high voltages from switching, such as inverters,
do not ground them together. Use an exclusive ground for each device.
The terminal block cover must be used for preventing electric shock.
5.8.2 Momentary Power Failures
Operation of momentary power failures
-
If the duration of the power failure is less than 10 ms, the FP-X0 control unit continues to operate. If the
power is off for 10 ms or longer, operation changes depending on the combination of units, the power
supply voltage, and other factors. (In some cases, operation may be the same as that for a power
supply reset.)
-
Although the duration of the power failure for the expansion FP0 adapter is 10 ms, judge the
permissible time for the system after confirming the permissible duration of the power failure for the DC
power supply that supplies power to the expansion FP0 adapter. (Supply the power to it from the
service power supply for the input of the FP-X0 control unit.)
-
When using the expansion unit with a built-in power supply (E30, expansion FP0 adapter), depending
on the duration of the momentary power failure, either one unit may be without electricity momentarily
and the I/O verify error may occur. In that case, turn off the power supply and then turn on again.
5.8.3 Protection of Output Sections
Protection of output
If current exceeding the rated control capacity is being supplied in the form of a motor lock current or a
coil shorting in an electromagnetic device, a protective element such as a fuse should be attached
externally.
Phone: 800.894.0412 - Fax: 888.723.4773 - Web: www.clrwtr.com - Email: [email protected]
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