Integrity monitor for ils receiver with automatic change of monitor threshold sensitivity

Claim 2

An integrity monitor for detecting faults in the airborne equipment of an aircraft radio navigation system, comprising a radio receiver for receiving beamed radio transmissions defining an aircraft course in space; means associated with said receiver producing a guidance signal output having a magnitude and sense dependent upon the displacement of said receiver from said defined course; duplicate means associated with said receiver normally producing a guidance signal which is the substantial duplicate of the guidance signal produced by said first named means; means for injecting a tracer signal in each of said guidance signal producing means; means at the outputs of said guidance signal producing means for comparing with one another said guidance signals each including said tracer signal to determine the difference between said guidance signals and the sum of said included tracer signals; means including a variable gain limiting amplifier receiving the output of said comparing means and producing tracer signal at the output thereof so long as said guidance signal difference is insufficient in magnitude to cause limiting of said amplifier; means responsive to the magnitude of one of said guidance signals for varying the gain of said amplifier; and means for producing an alarm whenever magnitude of tracer signal from said amplifier varies a predetermined amount.

Claim 3

An integrity monitor as claimed in claim 1 with additionally, means controlled by said means for varying said amplifier gain for adjusting the magnitude of said tracer signal.

Claim 4

In a navigation receiver for an aircraft instrument landing system having dual means for detecting tone modulations on a radio beam to provide two normally similar guidance signals, an integrity monitor comprising means for combining with each of said guidance signals an alternating current tracer signal; means for comparing said combined tracer-guidance signals with one another, said comparing means under normal conditions yielding a second tracer signal having an amplitude proportional to the sum of the amplitudes of said tracer signals, a variable gain amplifier for amplifying said second tracer signal; means controlling the gain of said amplifier to provide amplification in a greater amount whenever the magnitude of one of said guidance signals indicates that the aircraft bearing said receiver is relatively close to the desired course than when said magnitude indicates that said aircraft is relatively distant from the desired course; detecting means providing a direct voltage proportional to the amplitude of said amplified second tracer signal; and means for comparing said direct voltage with an established reference for producing an alarm whenever said direct voltage differs from said reference an appreciable amount.

Claim 5

In a navigation receiver for an aircraft instrument landing system having dual means for detecting tone modulations on a radio beam to provide two normally similar guidance signals, an integrity monitor comprising means for combining with each of said guidance signals an alternating current tracer signal; means for comparing said combined tracer-guidance signals with one another, said comparing means under normal conditions yielding a second tracer signal having an amplitude proportional to the sum of the amplitudes of said tracer signals, a variable gain amplifier for amplifying said second tracer signal; means controlling the gain of said amplifier to provide amplification in a greater amount whenever the magnitude of one of said guidance signals indicates that the aircraft bearing said receiver is relatively close to the desired course than when said magnitude indicates that said aircraft is relatively distant from the desired course; detecting means providing a direct voltage proportional to the amplitude of said amplified second tracer signal; and means for comparing said direct voltage with an established reference for producing an alarm whenever said direct voltage differs from said reference an appreciable amount.

Claim 6

An integrity monitor as claimed in claim 3, with additionally, means also controlled by said means controlling said amplifier gain for attenuating said tracer signals combined with said guidance signals whenever said amplifier gain is adjusted for greater amplification.

Claim 7

An integrity monitor as claimed in claim 4 wherein said amplifier includes limiting means and with additionally, means responsive to the signal levels of said modulations on said beam for biasing said limiting means into a condition of nonconduction of alternating current whenever said modulation signal levels change an intolerable amount.

Claim 8

An integrity monitor as claimed in claim 5, with additionally, means also controlled by said means controlling said amplifier gain for disabling said biasing means in the presence of increasing signal levels of said modulations whenever said amplifier gain is adjusted for lesser amplification.

Claim 9

In a navigation receiver for an aircraft instrument landing system having dual means for detecting tone modulations on a radio beam to provide two normally similar guidance signals, an integrity monitor comprising, a signal generator producing an alternating current tracer signal; controllable means for adjusting the level of said tracer signal at a relatively high and at a relatively low level; means for combining said controlled level tracer signal with each of said guidance signals; means for comparing said combined tracer-guidance signals with one another, said comparing means under normal conditions yielding a second tracer signal having an amplitude proportional to the sum of the amplitudes of the tracer signal components of said combined tracer-guidance signals; an amplifier having a controllable gain for amplifying said second tracer signal a relatively high amount in one gain control condition and a relatively low amount in another gain control condition; control means for controlling the gain of said amplifier and said level adjusting means to provide relatively low level tracer signal when said amplifier is controlled for relatively high amplification and to provide relatively high level tracer signal when said amplifier is controlled for relatively low amplification, said control means being responsive to said guidance signals to provide high gain-low level controls when the aircraft is relatively close to the desired course and to provide low gain-high level controls when the aircraft is relatively distant from the desired course; a limiting-type amplifier having as inputs a reference signal, the output of said controlled gain amplifier and a signal proportional to the levels of said guidance signals; detecting means providing a direct voltage proportional to the amplitude of the alternating current output of said limiting amplifier; and means for comparing said direct voltage with a second reference for producing an alarm whenever said direct voltage differs from said reference an appreciable amount.

Claim 10

In a navigation receiver for an aircraft instrument landing system having dual means for detecting tone modulations on a radio beam to provide two normally similar guidance signals, an integrity monitor comprising, a signal generator producing an alternating current tracer signal; controllable means for adjusting the level of said tracer signal at a relatively high and at a relatively low level; means for combining said controlled level tracer signal with each of said guidance signals; means for comparing said combined tracer-guidance signals with one another, said comparing means under normal conditions yielding a second tracer signal having an amplitude proportional to the sum of the amplitudes of the tracer signal components of said combined tracer-guidance signals; an amplifier having a controllable gain for amplifying said second tracer signal a relatively high amount in one gain control condition and a relatively low amount in another gain control condition; control means for controlling the gain of said amplifier and said level adjusting means to provide relatively low level tracer signal when said amplifier is controlled for relatively high amplification and to provide relatively high level tracer signal when said amplifier is controlled for relatively low amplification, said control means being responsive to said guidance signals to provide high gain-low level controls when the aircraft is relatively close to the desired course and to provide low gain-high level controls when the aircraft is relatively distant from the desired course; a limiting-type amplifier having as inputs a reference signal, the output of said controlled gain amplifier and a signal proportional to the levels of said guidance signals; detecting means providing a direct voltage proportional to the amplitude of the alternating current output of said limiting amplifier; and means for comparing said direct voltage with a second reference for producing an alarm whenever said direct voltage differs from said reference an appreciable amount.

Claim 11

An integrity monitor as claimed in claim 7 wherein said detecting means operates in synchronism with said tracer signal generator.