DESCRIPTION AND OPERATION
HSS MODULE CIRCUITRY
2 - 4
I-E96-315B
®
All the blocks of the support circuitry help the MCU direct
module activity and interface the control loop. Power enters the
board by way of the module mounting unit backplane. The
slave expander bus interface provides slave communication
with the processor module. The position demand circuitry per-
forms digital-to-analog conversion of position demands, while
the output circuitry amplifies the current driving the servo
valve coils. A dither oscillator prevents fuel valves from freezing
in one position. The position feedback block demodulates feed-
back from the LVDT secondary and converts it from an analog
signal to digital data. A frequency selectable (1, 2.5 or 10 kilo-
hertz) oscillator supplies the excitation voltage for the LVDT
primary. The digital I/O circuitry provides isolated DC inputs
that allows the operator to control the actuator position when a
module communication failure interrupts automatic control.
HSS MODULE CIRCUITRY
The following text explains the operation of the seven func-
tional blocks that make up the hydraulic servo slave module.
Figure 2-2. HSS Functional Block Diagram
MICRO-
CONTROLLER
STATUS AND
DATA STORAGE
XBUS
I/O
RAISE/LOWER
CONTACT INPUTS
DIGITAL I/O
POSITION FEEDBACK
POSITION DEMAND
DIGITAL I/O
LVDT OSCILLATOR
ISOLATION/
DEBOUNCE
DEMODULATOR
SAMPLE/HOLD
A/D CONVERTER
D/A CONVERTER
POSITION ERROR
AMPLIFICATION
DITHER OSCILLATOR
ISOLATION/
DEBOUNCE
EMERGENCY
MANUAL OUTPUT
LVDT
SECONDARIES
TRIP BIAS
CONTACT INPUT
LVDT
PRIMARY
OUTPUTS TO
SERVO VALVE
COILS
TP25014B
SLAVE EXPANDER BUS
