Fail-Safe Circuit Concept - Mitsubishi Q2ASCPU User Manual

(5) Install the unit far from any source of vibration, such as a large magnetic
contactor and a no-fuse breaker on the same panel, or install it on a
separate panel.
(6) Keep the following distance between the programmable controller and
other devices (such as a contactor and a relay) in order to avoid the
influence of radiated noise and heat:
a device installed in front of the programmable controller
....................................................................................... 100mm (3.94 inch) or more
a device installed on the right or left of the programmable controller
....................................................................................... 50mm (1.97 inch) or more
100mm (3.94inch)
or more

4.2 Fail-Safe Circuit Concept

When the programmable controller is powered ON and then OFF, improper
outputs may be generated temporarily depending on the delay time and start-up
time differences between the programmable controller power supply and the
external power supply for the control target (especially, DC).
For example, if the external power supply for the control target is powered ON and
then the programmable controller is powered ON, the DC output module may
generate incorrect outputs temporarily upon the programmable controller
power-ON. Therefore, it is required to build the circuit that energizes the
programmable controller by priority.
The external power failure or programmable controller failure may lead to the
system error.
In order to eliminate the possibility of the system error and ensure fail-safe
operation, build the following circuit outside the programmable controller:
emergency circuit, protection circuit and interlock circuit, as they could cause
machine damages and accidents due to the abovementioned failures.
An example of system design, which is based on fail-safe concept, is provided on
the next page.
Contactor, and
relay, etc.
21
50mm (1.97inch)
or more
50mm (1.97inch)
or more