D-2 Chadwick-Helmuth A Business Unit of Honeywell International, Inc.
Appendix D - 8520CS Signal Selector
D.3 Physical Description (Figure D-11)
The 8520CS has 8 discrete velocimeter single-channel connectors, 2 magnetic pickup/tracker
connectors, 2 discrete photocell connectors, 4 High Temp Accelerometers connectors (balanced
differential output type), a 28 VDC input power connector, a connector for receiving commands from
and transmitting selected signals to the 8500C/C+, and 2 multichannel connectors to interface with the
umbilical cables. All the inputs on the to of the units are available on these high density connectors.
D.4 Theory of Operation
D.4.1 Connector Harness
The 8520CS uses a connector harness as the 8520C does, to route signals to the singal conditioner and
controller boards. The top panel connectors are connected in parallel with the 2 high density umbilical
connectors J1 and J2. The intent of these high density connectors is to simplify installation on
permanently wired aircraft. The top connector and its corresponding high density pins are wired in
parallel and therefore should not be used at the same time.
D.4.2 A3 Controller Board
The 8520CS controller board A3 is a modified 8520C controller board. The modification is to allow
the signal conditioning PCB (A1) to be inserted between A3 and the harness. The contoller board
firmware has been modified to map the external channels to the proiper internal channel numbers. (See
Section 4.2.2.1 “ Controller Board”).
D.4.3 Signal Conditioner Board (Figure D-1)
This new board adds the following signal processing functions:
Two high speed photocell processor circuits.
Four High Temperature Accelerometer (balance differential output type) channels. (equivalent to
Chadwick-Helmuth’s 8225 integratiing charge converter).
The channel sensitivity calibration of these accelerometer channels is marked on a label on the unit.
(i.e. 50 pC/g’s 100 pC/g’s etc). Each channel sensitivity can be individually set:
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