DESCRIPTION AND OPERATION
HSS MODULE OPERATION
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I-E96-322A
®
HSS MODULE OPERATION
The HSS module interfaces the MFP module to a servo valve or
I/H converter, providing the MFP module with position control
of a fuel throttle valve or steam governor valve. The HSS mod-
ule microprocessor carries the workload. It is able to perform
multiple tasks with the help of the module support circuitry.
The microprocessor provides the intelligence (firmware) needed
to relay position demands from the MFP module, read position
feedback information, set targets for the output, and present
module status information to the MFP module, direct manual
control and perform self-check diagnostics. There are seven
functional blocks (see Figure
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I/O expander bus interface.
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Status and data buffers.
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Microprocessor.
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Position demand and output.
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Position feedback input.
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LVDT oscillator.
Digital I/OAll the blocks of the support circuitry help the
microprocessor direct module activity and interface the control
loop. Power enters the board by way of the module mounting
unit backplane. The I/O expander bus interface provides I/O
module communication with the multi-function processor
module. The position demand circuitry performs digi-
tal-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 posi-
tion. The position feedback block demodulates feedback from
the LVDT secondary and converts it from an analog signal to
digital data. A frequency selectable (400 hertz to 15 kilohertz)
oscillator supplies the excitation voltage for the LVDT primary.
The digital I/O circuitry provides isolated DC inputs to manu-
ally control the turbine throttle valve. If there is a communica-
tion failure between the MFP and HSS modules, this circuitry
enables the operator to control turbine speed. The digital I/O
circuitry provides a means to manually control the hydraulic
actuator position by sending a raise or lower signal to servo
valve or I/H converter.
