CSP−900RMM−2MD Helicopters, Inc.
Rotorcraft Maintenance Manual
Page 1
Revision 4
26-10-10
OVERHEAT BLEED AIR LEAK DETECTION
(HEAT/DEFOG) SYSTEM
DESCRIPTION AND OPERATION
1. Overheat Bleed Air Leak Detection
(Heat/Defog) System
(Ref. Figure 1)
The overheat bleed air leak detection system
consists of an overheat detection cable routed
around the length of the heat/defog bleed air
line located under the right side cabin floor,
and aft of the right side FS 230.5 bulkhead.
The cable is attached to a overheat control
unit located under the right side crew compart
ment floor.
2. Overheat Bleed Air Leak Detection
Components
A. Overheat Detection Cable
The overheat detection cable is a single
flexible semi-conductor type cable 0.070
inches in diameter. The cable construction
consist of one central conductor surrounded by
a highly compacted layer of manganese oxide
semi-conductor material covered by a stain
less steel double outer sheath. It is the
property of the semi-conductor that forms the
basis of operation for the detection cable.
The cable functions as a temperature averag
ing device, its absolute or base resistance
being a function of the surrounding ambient
temperature. As the cable temperature rises
its resistance drops until it reaches a predeter
mined set point of the control unit, at which
point the warning (CAB HEAT) is displayed
on the Integrated Instrument Display System
(IIDS) panel.
The use of a continuous loop enables the
system to be monitored for open circuit
condition. In the event of a single cable break,
the system remains operational. The connec
tors in the loop are ceramic cased or coated to
eliminate the possibility of a false alarm.
B. Overheat Control Unit
The overheat control unit is a loop connector
which detects the resistance drop in the
detection cable and emits a signal to the IIDS
display. Two channels, fault, and overheat are
interconnected and timed-phased in order to
discriminate against false warnings resulting
in a short in cable circuitry. In the event of an
overheat bleed air leak condition the IIDS will
shutoff the heat/defog system from the signal
received from the overheat control unit.
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