Combined radar/barometric altimeter
First Claim
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1. A method for supplying altitude signals to an output bus using radar and barometric altimeters, comprising the steps of:
- a. selecting the altitude signals from the radar altimeter for output to the output bus if a validity indicator shows them to be valid;
b. computing the change of altitude from the barometric altimeter over a given unit of time;
c. adding said change to the altitude signals on said output bus to provide corrected altitude signals; and
d. if the radar altitude signals are not valid, alternatively selecting said corrected altitude signals for output to the output bus;
the valid or not valid status of the radar altititude signals being used as the sole criteria whether to select the altitude signals from the radar altimeter or the corrected altitude signals.
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Abstract
An altitude sensing arrangement which combines the advantages of a barometric altimeter with a radar altimeter. The apparatus monitors the radar altimeter'"'"'s associated radar validity signal and selects the radar altimeter'"'"'s reading when the validity signal indicates a valid condition. Alternately, when the validity signal does not indicate a valid condition, the invention computes the difference in barometric altitude since the last valid radar altimeter reading and sums this difference with the last valid reading from the radar altimeter to produce a combined altitude reading.
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Citations
5 Claims
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1. A method for supplying altitude signals to an output bus using radar and barometric altimeters, comprising the steps of:
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a. selecting the altitude signals from the radar altimeter for output to the output bus if a validity indicator shows them to be valid; b. computing the change of altitude from the barometric altimeter over a given unit of time; c. adding said change to the altitude signals on said output bus to provide corrected altitude signals; and d. if the radar altitude signals are not valid, alternatively selecting said corrected altitude signals for output to the output bus; the valid or not valid status of the radar altititude signals being used as the sole criteria whether to select the altitude signals from the radar altimeter or the corrected altitude signals.
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2. Apparatus for determining the altitude of an aircraft with respect to the underlying terrain, for use with a radar altimeter having an associated validity signal output, and a barometric altimeter, and providing output data for an altitude indicator, said apparatus comprising:
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a radar input memory coupled to the radar altimeter, a barometric input memory coupled to the barometric altimeter, a validity bistable device coupled to said validity signal output, timing means which produces timing signals in cycles recurring at fixed intervals; the timing means having connections with signals effective during each cycle to load radar altitude in the radar input memory, the validity signal condition in the validity bistable device, and barometric altitude data in the barometric input memory; an output memory having an output to an output bus which is coupled to supply said output data to said altitude indicator, a control input from the timing means to the output memory; data select means having a control input from the validity bistable device, data input means from the radar input memory, and data output means coupled to the output memory, the data select means being enabled during every cycle in which the state of the validity bistable device indicates that the radar altitude data is valid to cause altitude data to be transferred from the radar input memory to the output memory, so that when the radar altitude data is valid the output data on the output bus represents solely the radar altimeter output; a second barometric memory having input connection means from the barometric input memory and the timing means enabled during each cycle before current cycle data is loaded into the barometric input memory to transfer the preceeding cycle data from the barometric input memory to the second barometric memory; adder means having positive data inputs from the barometric input memory and the output bus, a negative input from the second barometric memory, and a data output to a second data input means of the data select means; the data select means being alternatively enabled during cycles in which the state of the validity bistable device indicates that the radar altitude data is not valid to cause data to be transferred from the adder means output to the output memory, so that when the radar altitude data is not valid the output data on the output bus represents essentially the last valid radar altimeter output updated by the change of the barometric altimeter output; the valid or not valid status of the radar altitude signals being the sole criteria during each cycle as to whether to select the altitude signals from the radar altimeter or from the adder means. - View Dependent Claims (3, 4, 5)
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Specification