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Publication SAFETY-AT017B-EN-P-July 2011
Typical Reaction Time of Safety System
Typically, both channels are HI coming from the interlock switch and the
E-stop. If any one channel goes LO, the corresponding filter timer
configured in the 1791ES-IB8OBV4 module starts. If the channel is still
LO when the filter times out, the output is turned OFF.
Typically, the time it takes to occur is the sum of the A to E path as
described below.
A
B
C
D
A – Input Module delay / (max/2) = 8ms + on/off delay filters
E
B – Input Connection Reaction Time / Input RPI
C – GuardLogix Delay
The typical delay time for the GuardLogix controller is:
(Period / 2) + Task Scan Time
D – Output Connection Reaction Time / Output RPI = Task Period
E – Output Module Delay / (max / 2) = 3ms
Typical Reaction Time = A + B + C + D + E
Achieving a Cat. 4 Safety Rating
In order to achieve Cat. 4, modifications must be made to the bill of
materials, software configuration, and wiring schematic.
The Category 3 solution used a drive enable digital input to the drive and
the relay as switching signals to disconnect power to the motor. In that
solution, we had no means to monitor the status of the Drive Enable
digital input. In the Cat. 4 solution, we replace the Drive Enable input
with a safety contactor.