An encoder is disclosed for providing an accurate digital representation of the altitude of an aircraft vehicle by comparing an output signal from a pressure transducer which is a function of the barometric pressure at the altitude of the vehicle with an internally generated waveform which represents a curve of altitude vs. barometric pressure on its X--Y axis. The waveform is generated by a closed loop having an integrator circuit for providing the waveform, a comparator, a filter, a voltage controlled oscillator, and a counter, which all maintain the amplitude of the waveform within precise limits. The output signal from the transducer and the wave form from the closed loop are compared by a second comparator to provide a signal which transfers temporary information in the counter to a storage device which provides a coded digital output of the altitude of the vehicle.
A signal varying over a wide dynamic range from a source (10) is input to a summing amplifier (12) along with the output of an adjustable reference generator (14). An error signal output of the summing amplifier (12), a subtraction of the output of the reference generator (14) from the input signal source (10), is applied to a rate network consisting of a capacitor (16) and a resistor (18), with the latter in a feedback loop for an amplifier (20). The output of the reference generator (14) is adjusted to maintain the error signal within the operating limits of the summing amplifier (12) by monitoring the output of the amplifier. During the time interval when the adjustment of the generator (14) is made, a compensating network (24) maintains the output of the amplifier (20) at the level previous to the adjustment interval. This provides a continuous output voltage at a terminal (22) that varies over an expanded range with reference to the input signal.
An air data measurement system includes a device for sensing air pressure outside an aircraft, a pressure transducer in fluid communication with the air pressure sensing device and having a piezoresistive bridge attached on a flexible diaphragm. The piezoresistive bridge has an electrical resistance which varies in response to the sensed air pressure applied to the diaphragm and whose sensitivity varies with the magnitude of the excitation current passing therethrough. The system also includes a current supply operatively connected to the pressure transducer for supplying and varying the magnitude of the excitation current to the piezoresistive bridge. Further included is an output device connected to the pressure transducer for sensing a change in the electrical resistance of the piezoresistive bridge and outputting a signal from the piezoresistive bridge corresponding to the sensed air pressure. The current supply device varies the magnitude of the excitation current to the bridge in response to the output signal of the output device so as to change the sensitivity of the transducer relative to the airspeed of the aircraft.
A new and improved computing apparatus for determining aircraft altitude has a pressure transducer to sense atmospheric pressure at which the aircraft is located, and from this and a preset local ground level atmospheric pressure reading, actually solve a non-linear altitude-pressure equation. The computed altitude is used in conjunction with a time measurement to determine aircraft vertical rate. The computed altitude also specifies an address in a memory circuit, with the data stored at such address being the grey code which is transmitted to others for air traffic control purposes.
A combination altimeter and vertical speed indicator using digital displays. Digital logic technique are used to calculate vertical speed, eliminate drift in the vertical speed zero indication, correct vertical speed readings for altitude, and display altitude below zero. An automatic reading of barometric pressure setting for use as an offset is furnished at turn-on to permit initial setting of the instrument. Power to the instrument is pulsed to reduce consumption and permit long term battery operation.
This indicator preferably comprises two belts; one of the belts having graduations and the other belt a mark. This mark which has been preset to one of the graduations must be moved in the same manner as the graduated belt so that the agreement is maintained. According to the invention, two controls have been provided for driving these belts the input quantities whereof are processed by an arithmetic unit, for example a microprocessor.
