E-Stop Safety Relay
– Model ES-TA-3D1
SECTION 1 – Product Description
The purpose of safety relay model ES-TA-3D1 is to increase the control reliability of a
multiple-input 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 3, a typical Emergency Stop switch offers two redundant
switching contacts. In a properly designed machine stop circuit, the opening of either
of the two emergency stop contacts immediately removes electrical power from the
machine control elements which react to stop hazardous machine motion and/or any
other machine hazard. This redundancy of stopping control offered by a two-pole
Emergency Stop switch is the first step towards control reliability. However, failure or
defeat of one of the switch contacts to a short-circuit will go undetected, thereby
removing the redundancy, and leaving the Emergency Stop circuit prone to eventual
failure.
The ES-TA-3D1 safety relay connects up to six Emergency Stop switches to the
machine Emergency Stop control elements. The Emergency Stop switches become the
inputs to the safety relay. The safety relay monitors the condition of both contacts of
each Emergency Stop switch connected to it. The output of the safety relay consists of
two redundant output switching channels, each of which is the series connection of
two force-guided relay contacts (K1 and K2 in Figure 3).
As recommended by the Control Reliability section of ANSI B11.19, outputs of the
ES-TA-3D1 consist of two contacts (K1 and K2). These contacts are mechanically
linked, force-guided contacts, allowing the ES-TA-3D1 to monitor the outputs for
failures. If the safety relay detects failure of any contact of either the input Emergency
Stop switches or the output relays, the safety relay output is disabled and cannot be
reset. The two switching output circuits of the safety relay are rated for up to 250V ac
at up to 4 amps (resistive load).
The ES-TA-3D1 safety relay also provides a selectable (automatic or manual) reset
function.
WARNING. . .
Model ES-TA-3D1
Emergency Stop
Monitoring Safety
Relay is not a point-
of-operation guarding device, as
defined by OSHA regulations. It
is necessary to install point-of-
operation guarding devices, such
as safety light screens and/or
hard guards, to protect personnel
from hazardous machinery.
Failure to install point-of-
operation guards on hazardous
machinery can result in a
dangerous condition which could
lead to serious injury or death.
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