A digitally coded output is provided from a sensor, such as an aircraft angle of attack sensor. Groups of unused words from the complete unit distance table are omitted between groups of words that are selected to be used in the code, these unused words being "illegal" words indicating an error if they appear in the output of the sensor. The digitally encoded output of the sensor is, in the preferred embodiment, in unit distance code, and is fed to a programmed ROM where it is converted to binary or other convenient code, this binary encoded information representing the sensor output being employed to convey the information provided thereby. The output of the sensor is also fed to a second programmed ROM which has information stored therein indicative of which of the code words are "illegal". Whenever an illegal word is fed to this second programmed ROM, it generates a digital output indicating an error. This output is used to drive an alerting device to provide a warning to the operator that there is an error in the system's output. A third ROM is used to check the pairty of the code converting ROM to ensure detection of a ROM error.
Combinational logic circuits are used with a temporary storage device holding data bytes to detect improper bits in both the lower and upper nibbles of the bytes. Combinations of bit patterns derived from both nibbles permit flagging the occurrences of a variety of bit errors existing in sequentially transmitted parallel data bytes.
An electronic circuit for the generation of multiple breakpoint interrupts uses a plurality of RAMs (random access memory) wherein are stored bits such that, if all of the bit outputs of the RAM are active, then a breakpoint has been recognized. The logical combination of the RAM outputs determines the presence of a breakpoint.
An optical code reading device, including a unit having, for each of the tracks of the coded element, a pair of photodiodes, a differential amplifier receiving the outputs of the photodiodes and the trigger connected to the output of the amplifier, a shift register receiving the outputs from the unit, a control unit, a clock and apparatus for feeding to said unit signals adapted for simulating at will, for each channel, the bit level "0" or the bit level "1".
An apparatus and method for determining aircraft position and velocity is disclosed. The system includes two CCD sensors which take overlapping front and back radiant energy images of front and back overlapping areas of the earth's surface. A signal processing unit digitizers and deblurs the data that comprise each image. The overlapping first and second front images are then processed to determine the longitudinal and lateral relative image position shifts that produce the maximum degree of correlation between them. The signal processing unit then compares the first and second back overlapping images to find the longitudinal and lateral relative image position shifts necessary to maximize the degree of correlation between those two images. Various correlation techniques, including classical correlation, differencing correlation, zero-mean correction, normalization, windowing, and parallel processing are disclosed for determining the relative image position shift signals between the two overlapping images. The front longitudinal relative image position shift signal, the front lateral relative image position shift signal, the back longitudinal relative image position shift signal and the back lateral relative image position shift signal are then corrected by an altitude factor to respectively produce a front longitudinal ground distance signal, a front lateral ground distance signal, a back longitudinal ground distance signal, and a back lateral ground distance signal. These ground distance signals can be divided by the time delay between forming the first and second images to produce longitudinal and lateral ground velocity signals. The longitudinal and lateral ground distance signals can also be processed to produce other navigational measurements, such as the yaw, rotation, roll and ground track of the aircraft. The ground distance data and navigational measurements may be error checked against independent data and output to various displays.
