ENMET ISA-44-RALE-OD - Manual (Page 31)

ISA-44RALE-OD/ISA-44RAHE-OD/ISA-44E-OD ENMET Corporation
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7.3 Intrinsic Safety Barrier Replacement
If the oxygen channel encounters a significant power surge, the Intrinsic Safety Barrier will open (similar to a fuse). An
open I. S. barrier essentially sets the oxygen channel in alarm. This alarm condition differs from a regular oxygen alarm
in that the oxygen meter immediately falls to the bottom of the scale, the channel remains in alarm even if clean, oxygen
sufficient air is supplied to the oxygen cell, and there is no meter response to adjustments of the oxygen gain
potentiometer.
Note that a similar alarm condition occurs if the oxygen cell has reached the end of its life, the oxygen cell is removed
from the circuit, or if there is a bad connection in the oxygen channel circuitry. To determine whether or not the problem
is an intrinsic safety barrier, disconnect the power to the unit and declassify the area, then remove the display plate and
circuitry from the control unit (do not disconnect anything). At the bottom of the control unit is a mounting plate, on
which the I.S. barrier is attached. Check for electrical continuity across terminals 1 and 3 of the I.S. barrier. If there is not
continuity, the barrier has opened and must be replaced. If there is continuity, the problem involves some other
component or circuitry.
7.4 Sensor Hook-Up and Replacement for ISA-44E-OD
MOS sensors connect to the control unit with three conductors. Two conductors supply heater current to the sensor. The
third conductor is a signal wire. Size of heater wire depends on the distance between the particular sensor and the control
unit. For a distance of 250-1000 feet, 16 gauge wire is recommended.
Sensor wires correspond to the normal wire code (orange=heater; brown=ground; blue=signal).
N OTE : After you mount and install the ISA-44E-OD you MUST adjust the sensor heater voltage (see section 7.5).
Top View Side View, Cut-away
Figure 12A: Oxygen Cell Enclosure
Figure 12B: MOS Sensor Enclosure
Oxygen Cell
(Below PCB)
Clip for
Oxygen Cell
MOS Sensor
Sensor Shield
(Optional)
MOS Sensor
Enclosure Cover
Cut-away view