Precautions for monitoring the QCPU redundant system
(1) A system alarm may be detected when the system is switched in a redundant system.
When Q redundant setting is made
When Q redundant setting is not made : "402 Communication timeout. Confirm communication pathway or
However, even if the error occurs, the GOT automatically resumes monitoring and there are no problems in
the monitoring operation.
(2) The system alarm is displayed when the system is switched due to cable disconnection etc. (when the path is
The system alarm is not displayed when the system is switched by the user.
(3) When connected to the remote I/O station, the GOT can monitor only the following GOT functions.
(4) When connected to the remote I/O station, the GOT does not allow the PLC CPU clock of the master station
to be set in the clock setting of the utility.
The master station clock will not change even if the clock setting is made.
Use GX Developer or a similar software to set the PLC CPU clock of the master station.
(5) When the Q redundant setting is not made, the GOT does not automatically change the monitoring target
even if system switching occurs in the redundant system. When the GOT is connected to the standby system,
data written to a device are overwritten by the data of the control system, failing to be reflected.
In this case, when data are written to a device in the standby system normally, the system alarm "315 Device
writing error. Correct device." is not detected.
(6) For monitoring the QCPU redundant system when connecting to MELSECNET/H, use QCPU of function
version D or later, with the upper five digits later than "07102".
Also, use GX Developer of Version 8.29F or later.
(7) A message "Unable to communicate with CPU." is displayed when the system switching occurs while an
option function such as the ladder monitor is used.
(8) In the MELSECNET/H connection or MELSECNET/10 connection, when the control station of the
MELSECNET/H network or MELSECNET/10 network fails and is taken over by a station outside the QCPU
redundant system, the timeout is detected as the system alarm.
If this occurs, the monitor display speed may slow down.
(9) In the direct CPU connection, the GOT fails to automatically change the monitoring target in the following
• When the power supply to the CPU where the GOT is connected is OFF
• When the cable connecting the GOT with the CPU is broken
• When the tracking is disabled
(10) If the Q redundant setting is made for a system that is not a QCPU redundant system, no error occurs at the
start up of the GOT and the GOT operates normally.
In this case, if an abnormality (such as powering OFF, or communication timeout error) occurs at the PLC
CPU for which the Q redundant setting has been made, the PLC CPU may operate in a different way from the
monitoring target change mode that was set in the Q redundant setting.
(11) If the QCPU redundant system is in the debug mode, do not make the Q redundant system setting for the
GOT side when connecting the GOT.
: "450 Path has changed or timeout occurred in redundant system."
System monitoring function
4. HOW TO MONITOR REDUNTANT SYSTEM
4 - 7