Honeywell Chadwick-Helmuth 8500C User Manual

4-12 Chadwick-Helmuth A Business Unit of Honeywell International, Inc.
Chapter 4 - System Theory of Operation
The microcontroller controls electronic switches in the second 2:1 multiplexer, which
selects either the sum or difference output of the second sum/difference function block for
buffering and routing to the analog board of the 8500C/C+.
f. Peak Detect and Hold
. The peak detect and hold detects and holds the peak Velocimeter
input levels, which is used by the 8500C/C+ to look ahead at the next to-be-acquired
Velocimeter input. This enables the 8500C/C+ to set the input gain in the analog board
without delay after the next Velocimeter input has been selected.
g. Analog-to-Digital Converter
. The analog-to-digital converter (ADC) digitizes the peaks
from the peak detect and hold, which are used by the 8500C/C+ for gain setting.
h. 4:1 Multiplexers
. The microcontroller controls electronic switches which select one of
four azimuth pickup inputs for buffering and routing to a pulse detector.
The microcontroller controls electronic switches which select one of four azimuth pickup
inputs for buffering and routing to the pickup input of the digital board in the 8500C/C+.
i. Pulse Detector
. The pulse detector is identical to that used in the digital board of the
8500C/C+. The output of the detector is connected to the microcontroller. The input period
of the selected pickup is monitored and reported to the 8500C upon command.
j. Microcontroller
. The microcontroller is a very large scale integration microcontroller
which is used for all control and communication functions in the 8520C. The
microcontroller is an Hitachi 6303A. The microcontroller controls the timing of the
various multiplexers and switches of the controller board. The 6303’s built-in serial
communications controller is used for communications between the 8520C and the
8500C/C+.
4.2.2.2 Velocimeter BIT (Figure 4-6)
The Velocimeter BIT portion of the board determines the presence of a major failure (open or short) of
a Velocimeter or its cable. The board monitors the Velocimeter signal and searches for a characteristic
signature. If the Velocimeter signature is not recognized, the 8520C will inform the 8500C/C+ of the
failure.
a. Latch
. The latch controls the power switch. The controller board microprocessor writes a
control word to the latch.
b. Power Switch
. The power switch controls the +12 VDC and -12 VDC power to the
Vel ocimete rs .
c. Power Monitor
. The power monitor checks the +12 VDC and -12 VDC power lines. If
there is a short circuit present on the power lines, then the power monitor illuminates the
short circuit lamp.
d. Short Circuit Lamp
. The short circuit lamp indicates the presence of a short circuit on the
+12 VDC or -12 VDC power lines.
4.2.2.3 Power Supply Board (Figure 4-7)
The power supply board converts the 28 VDC input power from the aircraft to the DC voltages needed
to operate the circuit boards in the assembly. The input power from the aircraft can be 12 to 28 VDC of
either polarity. The input power is applied to a diode bridge to set the input voltage to the correct
polarity. The output of the bridge is applied across a FET switch and transformer. The transformer
outputs are rectified and filtered to produce +5 VDC, one +12 VDC, and one -12 VDC output voltage.

Honeywell Chadwick-Helmuth 8500C Specifications

General

Brand	Honeywell
Model	Chadwick-Helmuth 8500C
Category	Measuring Instruments
Language	English