Electric heating – Heating devices – With power supply and voltage or current regulation or...
Reexamination Certificate
2001-01-17
2001-12-04
Paschall, Mark (Department: 3742)
Electric heating
Heating devices
With power supply and voltage or current regulation or...
C219S501000, C219S212000, C219S497000, C338S026000, C340S398100
Reexamination Certificate
active
06326598
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to overheat detection systems of the type used in aircraft for monitoring duct leaks, and more particularly to an event location system useful for identifying the location of a leak.
BACKGROUND OF THE INVENTION
A large number of duct leak and overheat detection systems in operation today are zone-type systems. As with any duct leak and overheat detection system, sensor loops, comprising elongate sensing cables, are installed along the aircraft's bleed air duct and adjacent heat sensitive components. The sensors are configured in loops, and there are one or two loops for each zone being monitored. The problem with these systems is that during maintenance of the aircraft it is difficult to locate exactly where, along the length of the loop, the overheat event had occurred. In situations where faster maintenance action is warranted, the loops are broken down into smaller more manageable sections, but at the expense of more wires and associated weight. In cases where the loop is monitoring a very long section of ducting, such as that which might be associated with the auxiliary power unit in certain aircraft, troubleshooting a duct leak can take days to accomplish.
Systems have been configured for newer aircraft which incorporate a maintenance feature that automatically detects and displays the location of the overheat event. These systems utilize a controller which measures current into both ends of the cable loop, and performs a bridge-type calculation to determine or estimate where in the loop a fault had occurred. These systems often use special sensor cables of fairly precisely controlled resistance per unit length, and the controllers are configured such that event location and overheat detection are performed by common hardware and software.
The newer controllers, however, are not suitable for installation in existing aircraft with existing cable systems. To install a newer system in an existing aircraft would typically require the removal of the existing duct leak and overheat detection system, including the cables and the controller, and the replacement with a completely new system.
Components associated with the in-flight operation of the aircraft are certified for use only after extensive testing according to strict protocols. Thus, for example, if one were to attempt to modify an existing overheat detection system controller to provide it with event location capabilities, and the addition required an actual modification to the overheat detection controller, the entire controller would need to be retested and re-certified. This is particularly troublesome for aircraft operators because the event location system is intended solely for maintenance personnel, although it interfaces with the overheat detection system which is operative during flight. The overheat detection system provides indicators in the cockpit for signaling the pilot of any overheat conditions, and also has test buttons which allow the pilot to test the system, for example, during pre-flight checks. It would be highly undesirable to require re-certification of the overheat detection system solely to provide a maintenance capability to assist the maintenance personnel.
SUMMARY OF THE INVENTION
In view of the foregoing, it is a general aim of the present invention to provide an event location module capable of operating with existing overheat detection systems and which interfaces with those existing systems “non-intrusively”. By non-intrusively is meant that any normal electronic failure in the event location module will not affect the operability of the overheat detection system; in the preferred practice of the invention, the event location module interposes no electronic components in the existing overheat detection system.
Thus, it is a general object of the present invention to provide an event location module which can be retrofit to an aircraft using an existing overheat detection system, and without the necessity for re-certifying the overheat detection system.
A more specific object is to provide a monitoring module for use with an existing overheat detection system, configured to be commanded into operation in response to currents in the overheat detection loop at a level indicating an overheat event, and to perform calculations which identify the location of the event, then to store event information including at least location and preferably also time of event.
Test systems for existing overheat detection systems create currents in the loop to test for loop continuity. These currents, being at a relatively high level, can be mistakenly interpreted as an overheat event. In the normal “run mode” the typical overheat detection system drives both ends of the cable loop so as to draw very little current, then monitors for a higher current condition indicative of an overheat event somewhere in the loop. In the “test mode” the system switches to drive one end of the loop and ground the other, which tests the continuity of the loop, but also passes current at a level similar to an overheat event.
According to an important aspect of the invention, it is an object to determine whether the overheat detection system is in the run mode or the test mode by sensing the currents in the loop, and to record an overheat event only when such an event is detected in the run mode, but not in the test mode.
Stated more broadly, it is an object to record all overheat events detected in the normal run mode, but to ignore, for purposes of recording, those “events” which are produced in the test mode.
Other objects and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 2483793 (1949-10-01), Thomas
patent: 5185594 (1993-02-01), DeChurch
patent: 5294909 (1994-03-01), Frazier
patent: 5313185 (1994-05-01), DeChurch
Carvalho Carlos E.
Hallee Donald O.
Kidde Technologies, Inc.
Leydig Voit & Mayer Ltd
Paschall Mark
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