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When Designing your GLC System:
- Be sure to design your GLC control system so that in the event of
a main power supply failure or a GLC accident, the user system’s
overall safety integrity will be maintained. If this is not done, in-
correct output signals or a GLC malfunction may cause an acci-
dent.
(1) Interlock circuits, etc. designed to interrupt or oppose normal
machine movement (i.e. Emergency Stop, General Protection,
forward and reverse rotation, etc.), as well as those designed
to prevent machine damage (i.e. for upper, lower and traverse
movement limit positioning, etc.) should all be designed to be
located outside of the GLC.
(2) Whenever the GLC generates a “Watchdog Timer Error”, GLC
operation will halt. Also, when errors occur in Input/Output
control areas that the GLC cannot detect, it is possible for
unexpected movement to occur in those areas. As a result,
for the purpose of preventing unsafe machine movement, a
“Failsafe Circuit” should be created which is completely ex-
ternal to the GLC.
(3) If a problem arises with an external unit’s relay or transistor,
causing an output (coil) to remain either ON or OFF, a major
accident can occur. To prevent this, be sure to set up external
watchdog circuits that will monitor vital output signals.
- Be sure to design a circuit that will supply power to the GLC’s I/O
unit before starting up the GLC. If the GLC’s internal program
enters RUN mode prior to the I/O unit’s load control power turn-
ing ON, an incorrect output (signal) or malfunction could cause
an accident to occur.
- Be sure to design a program that will ensure the safety of the
user’s system, in the event of a GLC display or control error, or in
the event of either a data transmission error or power failure be-
tween the GLC and a connected unit. These types of problems
can lead to an incorrect output (signal) or malfunction, which could
thereby cause an accident to occur.
-
Do not create GLC touch panel switches that could possibly en-
danger the safety of equipment and personnel. Damage to the GLC,
its I/O unit(s), cable(s), and other related equipment can cause an
output signal to remain continuously ON or OFF and possibly cause
a major accident. Therefore, design all monitoring circuits using
limit switches, etc. to detect incorrect device movement. To pre-
vent accidents related to incorrect signal output or operation, de-
sign all switches used to control vital machine operations so they
are operated via a separate control system.
DANGERS
