Chapter4 Precautions For Use Of Safety Plc; Precautions For Designing Safety Application - Mitsubishi Electric Melsec-QS Series Safety Application Manual

4
PRECAUTIONS FOR USE OF SAFETY PLC

CHAPTER4 PRECAUTIONS FOR USE OF SAFETY PLC

The safety standards conformance approval must be made by the user for the entire
safety-related system.
The safety system inspection is made for the entire safety-related system including safety
components and a sequence program.
The sample program is shown in Chapter 5. However, the safety standards approval is not
obtained.
And all work for safety-related system construction (e.g. design, installation, operation,
maintenance) has to be handled by the person who has an enough education concerning
safety standards, safety devices, and safety PLC.

4.1 Precautions for Designing Safety Application

(1) Response time
(2) Target failure measure (PFD/PFH) calculation
PFD/PFH = A + B + C + D
Variable
A
B1
B2
C *1
D
*1
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4.1 Precautions for Designing Safety Application
- 1
The response time is a time from the safety input OFF to the safety output OFF using
the safety PLC.
The response time is needed for determining the safety distance for a safety-related
system.
Calculate the response time of a system to be configured with referring to Appendix.1.
POINT
POINT
For the safety PLC, connecting GX Developer makes the response time longer.Do
not constantly connect GX Developer during the safety-related system operation.
Target failure measure (PFD/PFH) is the target value of reliability for each SIL level
standardized in IEC61508.(
Calculate the target failure measure (PFD/PFH) with the following formula for each
safety function.
Calculation formula of PFD/PFH
Table4.1 Definition of each variable
PFD/PFH of safety CPU module, safety power supply module, safety main base unit, and
CC-Link Safety master module
(1) The safety input device and safety output device are connected to the same safety
remote I/O module.
(2) The safety input device and safety output device are connected to the different safety
remote I/O modules.
PFD/PFH of the safety remote I/O module to which the safety input device is connected
PFD/PFH of the safety remote I/O module to which the safety output device is connected
PFD/PFH of safety input equipment
PFD/PFH of safety output equipment
*1: For PFD/PFH of C and D, refer to the manuals, etc. of the used safety components.
Section 3.3)
Definition