ISA-40 Oxygen Monitor
ENMET
Corporation
9
3.2.6 Intrinsic Safety
The output of the oxygen deficiency transducer cell is approximately 175 micro-Amps at 0.05
V
DC
in fresh air.
Therefore, the cell itself is not a source of ignition. If the cell leads are accidentally connected across 110
V
AC
or
12
V
DC
, the cell explodes and becomes an ignition source. If the sensor assembly is used in a hazardous atmosphere as
defined in the National Electrical Code, an approved intrinsic safety barrier (Stahl type 8901/31 or equivalent) must be
used at the cell wiring junction in the control unit enclosure. The intrinsic safety barrier is an option that can be
selected at the time of system specification, or it can be purchased separately. Also, the sensor assembly audio alarm
is not approved for use in a hazardous atmosphere.
W
ARNING
:
If an intrinsic safety barrier is used, the barrier
Must
be the junction between the oxygen cell and the
sensor connection o the
ISA-40
motherboard. See the wiring information Table 2A and Figure 4.
3.3 Relay Outputs
Relay contacts can be used to activate other alarm signals or equipment away from the control unit enclosure when
there is an alarm condition and when the
AC
or
DC
power is interrupted. The contacts supplied are dry, with a rating of
2
Amp
continuous, 5 Amp surge. Do not overload the
ISA-40
power supply by connecting it through the relay
contacts to an inappropriate load. See Wiring Information Tables 3 & 4 and Sections 3.3.1 and 3.3.2 and the Figure 6
Utilizing Relay Contacts.
Internal view of
ISA-40
Suggested wiring configuration for utilizing relay contacts
(manual on/off switch is suggested; user supplied component)
Figure 6: Utilizing the Relay contacts
Normally
Closed
Contact
Common
Contact
110 V
AC
Power supply Outside
of Control Unit
Manual On/Off
Switch
Horn
White
Black
TB7 inside Control Unit;
Location of latching
relay contact terminals
TB3 inside Control Unit;
Location of non-latching
relay contact terminals
TB7
T
B
3