E-Stop Safety Module Description
The purpose of an Emergency Stop Safety Module (E-Stop Safety Module) is to increase
the control reliability of an emergency stop circuit. The ANSI B11.19 standard states:
“Control reliability of electrical, electronic, or pneumatic systems
frequently consists of multiple, independent parallel or series circuitry
or components so arranged that any single failure ...
either sends a
stop command to the machine tool or prevents a successive cycle
from being initiated.”
As indicated in Figure 2, the model ES-..A-5A E-Stop Safety Module is designed for use
with a 1-channel or 2-channel E-stop switch. A 2-channel E-stop switch has two
electrically isolated contacts.
The user-supplied E-stop switch must be a “positive-opening device.” This means its
contacts will open when the actuator is pushed with a certain minimum force, even if a
contact has welded closed.
EN 954-1 Safety Categories
Both contacts of a 2-channel E-stop switch are monitored by the Safety
Module. If either input is short-circuited, the Safety Module cannot be reset,
and the controlled machinery cannot be restarted, following actuation of the
E-stop switch. Two-channel E-stop switches used with this Safety Module
are suitable for Safety Category 4 applications, per European Standard EN
954-1. Category 4 is the highest safety category (see EN 954-1 for further
information).
As shown in Figure 2, the E-stop switch becomes an input to the E-Stop
Safety Module. The Safety Module monitors the condition of both contacts
of the E-stop switch.
Use of a 1-channel E-stop switch provides no input redundancy, and no
ability for the Safety Module to monitor for input short circuits. One-channel
E-stop switches used with this Safety Module are generally suitable only for
Safety Category 2 applications, per EN 954 (see page 6).
NFPA79 Functional Stop Categories
In a functional Category 0 emergency stop circuit, the opening of either of
the two E-stop switch contacts (or the one contact, if configured to 1-
channel) immediately removes electrical power from the machine control
elements, which react to stop hazardous machine motion and/or other
machine hazards. This redundancy of stopping control offered by a two-pole
E-stop switch is the first step towards control reliability in an emergency
stop circuit.
The output of this E-Stop Safety Module consists of four redundant
output switching channels, each of which is the series connection of two
forced-guided relay contacts (K1 and K2 in Figure 2). The four switching
output circuits of the E-Stop Safety Module are rated for up to 250V ac at
up to 5 amps.
E-Stop Safety Module
– Models ES-GA-5A and ES-HA-5A
Input
Power On
K1 Energized
K2 Energized
Power Supply Fault
Ground Fault
Input Cross-short
K1
K2
K3
Power
Fault
Ch.1
Ch.2
Machine Safety
ES-GA-5A
B2 S31 14 24 34 44 52
S32
A2
S33 S32 S35 S21 S22
S11
A1
S12 Y30 Y31 Y32 Y35
S34
B1
13 23 33 43 51
Figure 1. ES-...A-5A Status indicators and
terminal locations
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