Safety Function Realization: Risk Assessment; Safety Function Requirements; Functional Safety Description - Allen-Bradley GuardLogix 5570 Original Instructions Manual

Enabling Switch with an Integrated Safety Controller and a POINT Guard I/O Safety Module Safety Function Application Technique

Safety Function Realization: Risk Assessment

The Performance Level required (PLr) is the result of a risk assessment and refers to the amount of the risk reduction to be conducted by the
safety-related parts of the control system. Part of the risk reduction process is to determine the safety functions of the machine. In this
application, the Performance Level that is required by the risk assessment is category 3, Performance Level d (cat. 3, PLd), for each safety
function. A safety system that achieves cat. 3, PLd, or higher, can be considered control reliable. Each safety product has its own rating and
can be combined to create a safety function that meets or exceeds the PLr.
From: Risk Assessment (ISO 12100)
1. Identification of safety functions
2. Specification of characteristics of each function
3. Determination of required PL (PLr) for each safety function
To: Realization and PL Evaluation
Enabling Switch Safety Function
This application technique includes one safety function: removal of power from the hazard when the safety system detects that the operator
does not have the enabling switch in the middle position, or the door switch is open.

Safety Function Requirements

Functional safety requires the continuous actuation of a three-position enabling switch to enable power to the motor. The handheld device
provides power to the motor when squeezed to the middle position. When the operator releases or fully squeezes the switch, power to the
motor is removed. Faults at the enabling switch, wiring terminals, or safety controller are detected before the next safety demand. The
safety function in this example is capable of connecting and interrupting power to motors rated up to 9 A, 600V AC.
The safety function in this application technique meets or exceeds the requirements for Category 3, Performance Level d (Cat. 3, PLd), per
ISO 13849-1 and control reliable operation per ANSI B11.19.

Functional Safety Description

In this example, power to the motor is enabled if the safety door is closed, or if the operator opens the door and squeezes an enabling switch
to the middle position. Both the door switch and enabling switch are wired to a pair of safety inputs on a safety input module (SI1).The safety
contactors (K1 and K2) are connected to a pair of safety outputs of a safety output module (SO1). The I/O module is connected via CIP Safety™
technology over an EtherNet/IP™ network to the safety controller (SC1). The safety code in SC1 monitors the status of the door and enabling
switch by using pre-certified safety instructions. Dual Channel Input Stop (DCS) is used for the door and Dual Channel Input Start (DCSRT) is
used for the enabling switch, as this device is a safety device that starts a safety output. When all safety input interlocks are satisfied and no
faults are detected, a certified function block called Configurable Redundant Output (CROUT) controls and monitors feedback for a pair of
100S redundant contactors.
Rockwell Automation Publication SAFETY-AT125C-EN-P - February 2022 5