TM 11-6625-3081-23
1-24.
TEST CONSOLE TEST BENCH 2A2
1-24
a.
GENERAL
Refer to FO-19 for a block diagram of the test console test bench. The test
console test bench is described in the following order:
Programmable digitizer 2A2A1
VHF cable entry panel 2A2A2
Optical signal generator assembly 2A2A3
Test adapter panel assembly 2A2A4
Multiprogrammer assembly 2A2A6
Electronics drawer assembly 2A2A7
Extender assembly 2A2A8
Matrix switch assembly 2A2A1O
Multiprogrammer extender assembly 2A2A11
Switch controller assembly 242A12
Analog to digital converter assembly 2A2A13
b.
PROGRAMMABLE DIGITIZER 2A2A1
(1) General.
The programmable digitizer 2A2A1 (FO-20) is a microprocessor-based,
dual-channel waveform-digiti zing instrument used to digitize video inputs, provide the
system clock, and perform measurements.
Analog signals are accepted under program
control by two plug-in programmable amplifiers and stored in a high-speed semiconduc-
tor memory for subsequent transfer over the IEEE 488 bus. Front panel (local) control
is accomplished by pressing the appropriate function key and decreasing or increasing
the parameter with the DECREMENT/INCREMENT keys.
The parameter cycles through only
those values which are valid for the current state of the digitizer, minimizing the
possibility of error.
The digitizer checks the settings each time the ARM button is
pressed in local mode or the ARM command is received in remote mode. Errors are
reported on the front panel and over the IEEE 488 bus.
(a) Analog to digital conversion is performed by two special electron-
bombarded semiconductor (EBS) tubes (one per channel). The EBS tube is an electron
tube with a silicone-diode target at one end and an electron gun at the other. The
target consists of a set of diodes fabricated in vertical stripes with parts of the
stripes masked by a thick metal film to form a gray-code pattern.
The electron gun
produces a lo-kilovolt beam which strikes an area of the target that is exposed,
causing the diode to conduct, generating an output current.
Each diode stripe defines
one bit in the eight-bit, gray-code output, so the output code from the target defines
the vertical position of the beam.
By applying the analog-input voltage to the verti-
cal deflection plates of the tube and sampling the digital output, the analog signal
is digitized.
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