GLC2400/2500/2600 Series User Manual
7
Preface
(2) When 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, unex-
pected movement may occur in those areas. Therefore,
and to prevent unsafe machine movement, a “Failsafe
Circuit” should be created which is completely external
to the GLC.
(3) If a problem arises with an external unit’s relay or tran-
sistor, 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 moni-
tor vital output signals.
• Design a circuit that will supply power to the GLC unit’s
I/O before starting up the GLC. If the GLC unit’s internal
program enters RUN mode prior to the I/O unit’s load con-
trol power turning ON, an incorrect output (signal) or mal-
function could cause an accident.
• Design a user program that ensures the safety of the user’s
system, in the event of a GLC display or control error, or
either a data transmission error or power failure between
the GLC and a connected unit. These types of problems
can lead to an incorrect output (signal) or malfunction, re-
sulting in an accident.
•
Do NOT make switches using the switches on the touch
panels which may cause operator injury and machine dam-
age. An output may remain either ON or OFF and a major
accident can occur. To prevent this, set up circuits such as
limiters that will monitor vital output signals. Design
switches for important operations to be performed by sepa-
rate devices. An incorrect output or malfunction can occur
and thereby cause an accident.
• Do NOT use GLC touch panel switches to perform operator
safety-related or important accident-prevention operations.
These operations should be performed by separate hardware
switches to prevent operator injury and machine damage.
DANGERS