Barometric altimeter
First Claim
1. Pressure altitude measuring apparatus comprising:
- a pressure sensor which produces a first electrical signal representing the atomospheric pressure at the altitude to be measured and containing a pressure transducer that produces an electrical output in response to the pressure applied thereon and an output stage with a resistor circuit to compensate for the offset value of the electrical output of said pressure transducer and a resistor circuit to adjust the magnitude of said first electrical signal,means to produce at least one kind of second electrical signals approximately equal respectively to the electrical signals which would be produced by said pressure sensor when the atmosheric pressure of at least one kind of altitude measuring reference altitudes is applied thereon,a quasi-exponential function generator comprising a capacitor circuit with two terminals, a discharge resistor circuit with two terminals and a controller, said two terminal discharge resistor circuit comprising at least one resistor and at least one switch for said function generation and controlled to provide an effective resistance which decreases with time by means of controlling said at least one switch for said function generation by said controller, and each of said two terminals of said discharge resistor circuit is connected to each of said two terminals of said capacitor circuit,means to generate a third electrical signal by means of charging said capacitor circuit of said quasi-exponential function generator with an electrical voltage determined in relation to the magnitude of the signal of the largest one of said at least one kind of second electrical signals, and discharging through said discharge resistor circuit for a predetermined discharging period in which said controller controls to decrease the effective resistance of said discharge resistor circuit,counting means to count electrical pulses of a predetermined frequency,means to control said counting means to count said electrical pulses only during the time interval in which the magnitude of said third electrical signal is approximately not more than the magnitude of one of said second electrical signals and not less than the magnitude of said first electrical signal,a temperature sensing device including temperature sensor, said device exhibiting plural electrical states according to the temperature of said pressure sensor and said quasi-exponential function generator,temperature compensation means comprising at least one of the following four means;
(1) means to change the electrical capacity of said capacitor circuit of said quasi-exponential function generator including controlling switches for temperature compensation incorporated in said capacitor circuit,(2) means to change the resistance of said discharge resistor circuit of said quasi-exponential function generator including controlling switches for temperature compensation incorporated in said discharge resistor circuit,(3) means to change the resistance of said resistor circuit to compensate for the offset value in said output stage of said pressure sensor including controlling switches for temperature compensation incorporated in said resistor circuit to compensate for the offset value,(4) means to change the resistance of said resistor circuit to adjust the magnitude of said first electrical signal in said output stage of said pressure sensor including controlling switches for temperature compensation incorporated in said resistor circuit to adjust the magnitude of said first electrical signal, according to said electrical states of said temperature sensing device,wherein a temperature compensated pressure altitude is obtained in said counting means.
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Accused Products
Abstract
The altitude of an aircraft is determined by measuring the output of a pressure transducer on the aircraft because the altitude is defined by the atmospheric pressure at that point. In this altitude measurement, the relationship between the altitude and the atmospheric pressure is nonlinear, and most pressure transducers exhibit some nonlinearity. High accuracy altitude measurement, correcting those nonlinearities, have been disclosed in the prior art utilizing a quasi-exponential function generator (QEFG). A quasi-exponential function is an exponential function with a time constant which varies with time. However, the characteristics of the pressure transducer and QEFG are affected by temperature, and there have been no appropriate means other than the use of a thermostat to maintain the accuracy of measurement when the temperature varies. This invention compensates for the temperature variant characteristics of the pressure transducer and the QEFG by changing the constants of the circuit elements of the QEFG and of the output stage coupled to the pressure transducer according to the output of a temperature sensor incorporated in the altimeter. Even the change of nonlinearity, or the change of curvature of the characteristic curve of the pressure transducer is compensated for almost perfectly by this invention.
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Citations
26 Claims
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1. Pressure altitude measuring apparatus comprising:
- a pressure sensor which produces a first electrical signal representing the atomospheric pressure at the altitude to be measured and containing a pressure transducer that produces an electrical output in response to the pressure applied thereon and an output stage with a resistor circuit to compensate for the offset value of the electrical output of said pressure transducer and a resistor circuit to adjust the magnitude of said first electrical signal,
means to produce at least one kind of second electrical signals approximately equal respectively to the electrical signals which would be produced by said pressure sensor when the atmosheric pressure of at least one kind of altitude measuring reference altitudes is applied thereon, a quasi-exponential function generator comprising a capacitor circuit with two terminals, a discharge resistor circuit with two terminals and a controller, said two terminal discharge resistor circuit comprising at least one resistor and at least one switch for said function generation and controlled to provide an effective resistance which decreases with time by means of controlling said at least one switch for said function generation by said controller, and each of said two terminals of said discharge resistor circuit is connected to each of said two terminals of said capacitor circuit, means to generate a third electrical signal by means of charging said capacitor circuit of said quasi-exponential function generator with an electrical voltage determined in relation to the magnitude of the signal of the largest one of said at least one kind of second electrical signals, and discharging through said discharge resistor circuit for a predetermined discharging period in which said controller controls to decrease the effective resistance of said discharge resistor circuit, counting means to count electrical pulses of a predetermined frequency, means to control said counting means to count said electrical pulses only during the time interval in which the magnitude of said third electrical signal is approximately not more than the magnitude of one of said second electrical signals and not less than the magnitude of said first electrical signal, a temperature sensing device including temperature sensor, said device exhibiting plural electrical states according to the temperature of said pressure sensor and said quasi-exponential function generator, temperature compensation means comprising at least one of the following four means; (1) means to change the electrical capacity of said capacitor circuit of said quasi-exponential function generator including controlling switches for temperature compensation incorporated in said capacitor circuit, (2) means to change the resistance of said discharge resistor circuit of said quasi-exponential function generator including controlling switches for temperature compensation incorporated in said discharge resistor circuit, (3) means to change the resistance of said resistor circuit to compensate for the offset value in said output stage of said pressure sensor including controlling switches for temperature compensation incorporated in said resistor circuit to compensate for the offset value, (4) means to change the resistance of said resistor circuit to adjust the magnitude of said first electrical signal in said output stage of said pressure sensor including controlling switches for temperature compensation incorporated in said resistor circuit to adjust the magnitude of said first electrical signal, according to said electrical states of said temperature sensing device, wherein a temperature compensated pressure altitude is obtained in said counting means. - View Dependent Claims (3, 5, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
- a pressure sensor which produces a first electrical signal representing the atomospheric pressure at the altitude to be measured and containing a pressure transducer that produces an electrical output in response to the pressure applied thereon and an output stage with a resistor circuit to compensate for the offset value of the electrical output of said pressure transducer and a resistor circuit to adjust the magnitude of said first electrical signal,
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2. Pressure altitude measuring apparatus comprising:
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a pressure sensor which produces a first electrical signal representing the atmospheric pressure at the altitude to be measured and containing a pressure transducer that produces an electrical output in response to the pressure applied thereon and an output stage with a resistor circuit to compensate for the offset value of the electrical output of said pressure transducer and a resistor circuit to adjust the magnitude of said first electrical signal, means to produce at least one kind of second electrical signals approximately equal respectively to the electrical signals which would be produced by said pressure sensor when the atmospheric pressure of at least one kind of altitude measuring reference altitudes is applied thereon, a quasi-exponential function generator comprising a capacitor circuit with two terminals and a discharge resistor circuit with two terminals and a controller, said capacitor circuit comprising a main capacitor which forms the main part of the capacity of said capacitor circuit and plural number of sectional capacitors which are connected in parallel to said main capacitor respectively by plural number of switches for said function generation, and said controller controls said plural number of switches for said function generation, and said controller controls said plural number of switches for said function generation to disconnect said plural number of sectional capacitors in a sequence of time from said main capacitor, and each of said two terminals of said discharge resistor circuit is connected to each of said two terminals of said capacitor circuit, means to generate a third electrical signal by means of charging said capacitor circuit of said quasi-exponential function generator with an electrical voltage determined in relation to the signal of the largest one of said at least one kind of second electrical signals, and discharging through said discharge resistor circuit for a predetermined discharging period which said controller controls to disconnect said sectional capacitors from said main capacitor in a sequence of time, counting means to count electrical pulses of a predetermined frequency, means to control said counting means to count said electrical pulses only during the time interval in which the magnitude of said third electrical signal is approximately not more than the magnitude of one of said second electrical signals and not less than the magnitude of said first electrical signal, a temperature sensing device including temperature sensor, said device exhibiting plural electrical states according to the temperature of said pressure sensor and said quasi-exponential function generator, temperature compensation means comprising at least one of the following four means; (1) means to change the electrical capacity of said capacitor circuit of said quasi-exponential function generator including controlling switches for temperature compensation incorporated in said capacitor circuit, (2) means to change the temperature of said discharge resistor circuit of said quasi-exponential function generator including controlling switches for temperature compensation incorporated in said discharge resistor circuit, (3) means to change the resistance of said resistor circuit to compensate for the offset value in said output stage of said pressure sensor including controlling switches for temperature compensation incorporated in said resistor circuit to compensate for the offset value, (4) means to change the resistance of said resistor circuit to adjust the magnitude of said first electrical signal in said output stage of said pressure sensor including controlling switches for temperature compensation incorporated in said resistor circuit to adjust the magnitude of said first electrical signal, according to said electrical states of said temperature sensing device, wherein a temperature compensated pressure altitude is obtained in said counting means. - View Dependent Claims (4, 6)
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Specification