(11)
The reliability signal generated in the range computer circuits is 28 vdc for the track condition and 0 vdc for a no-track condition. The external range amplifier is the output stage of the range computer circuits. The external range voltage (altitude signal) is from zero to -10 vdc, corresponding to altitudes from zero to 2,500 feet. Also, the external range amplifier contains the capability of being driven from an external signal applied, such as the failure drive signal. The failure drive or cruise monitor (above 2500 feet) drive signal is generated in the remote indicator.
(12)
The indicator converts the linear zero to -10 vdc external range voltage to a pointer/dial display of altitude at altitudes less than 2,500 feet. This signal is converted to a three-segment trilinear voltage by three scaling amplifiers. The trilinear voltage matches the three-segment dial display where graduations are expanded at the lower altitudes. The outputs of the scaling amplifiers feed a linear current amplifier/driver which provides a zero to 20-ma current to the meter movement. The cruise monitor circuitry monitors system performance at altitudes above terrain exceeding 2,500 feet. If the normal altitude range of 2,500 feet is exceeded, the reliability signal from the receiver-transmitter will switch to a no-track condition. System performance is checked once every five seconds as long as the 2,500 -foot altitude range is exceeded. In addition, the indicator has the following features:
(a)
Advancing the function knob clockwise allows the pilot to select a low altitude trip setting throughout the full range.
(b)
Depressing the knob actuates a test switch which allows the system self-test function to engage.
(c)
In the event of loss of track, the altitude pointer moves to a point above 2500 feet and disappears behind the NO TRACK mask.
(13)
The ARINC output circuit is composed of four operational amplifiers that rescale the external range output signal to a linear-logarithmic signal as defined in ARINC characteristic number 552A. From zero to 500 feet, the output signal is linear. From 500 to 2,500 feet, the ARINC output signal is logarithmic. The ARINC signal varies from zero to +26.174 vdc. The high and low altitude trip circuits switch from 28 vdc to 0 vdc when their PRESET trip level is passed during aircraft descent.
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B. Self-Test Operation
(1)
The self-test mode of operation is the manually commanded mode. It provides end-to-end checkout of the receiver-transmitter, exercising all the major functional blocks. By interpretation of the results of self-test, faults can be generally isolated to the receiver-transmitter, the indicator, or the antenna system. The self-test altitude indication is set at 400 feet.
(2)
The self-test sequence begins when the PUSH TO TEST knob on the indicator is pressed. This applies a ground to the input of the self-test gate, causing its output to become positive. This ground is also applied to the clamping circuits on the input to the T-zero amplifier, preventing the normal T-zero output of the transmitter circuit from being applied. The output of the prf generator, coupled through the PTT delay circuit and a differentiating circuit, is applied to the self-test gate as a high of approximately 5 volts with a width of 2,000 nanoseconds. This signal is then coupled through another gate circuit to the T-zero amplifier.
(3)
In the self-test mode of operation, the input to the T-zero amplifier is the differentiated leading edge of the prf generator output signal. Because of the time difference between the transmitted pulse and the self-test input to the T-zero amplifier, the receiver-transmitter develops an output range signal equal to the preset self-test altitude. When the transmitter fires, a leakage pulse is generated and travels to the receiver input. While the system is in the push-to-test mode, the leakage signal from the transmitter cavity to the receiver input (mixer/local oscillator) is outside the range of src (zero to 200 feet). During normal operation, all leakage signals are controlled by the src.
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LOW RANGE RADIO ALTIMETER SYSTEM - TROUBLE SHOOTING
EFFECTIVITY
GJ ALL EXCEPT B-2509, B-2510
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