OVERVIEW
I-E96-322A
1 - 1
SECTION 1 - INTRODUCTION
OVERVIEW
The IMHSS03 Hydraulic Servo Module is a valve position con-
trol module. It provides an interface through which a processor
module can control a hydraulic actuator via a servo valve. By
regulating the current to the servo valve, it initiates a change in
actuator position. A linear variable differential transformer
(LVDT) provides actuator position feedback to the hydraulic
servo (HSS) module. Typical uses for the HSS module are posi-
tioning of steam turbine throttle and control valves, gas tur-
bine fuel valves, inlet guide vanes and nozzle angle.
INTENDED USER
Anyone who installs, operates and maintains the HSS module
should read and understand this instruction before placing it
into service. Installation, troubleshooting and replacement
requires a technician or engineer with experience handling
electronic circuitry and analog control tuning experience. Addi-
tionally, experience with hydraulic actuators, servo valves, I/H
converters and associated hardware installation and calibra-
tion is required. Operation and maintenance requires an indi-
vidual who knows turbine start-up and plant operating
procedures.
HSS MODULE DESCRIPTION
The HSS module is an intelligent I/O module with micropro-
cessor, memory and communication circuitry. The module
consists of a printed circuit board attached to a faceplate. Nine
status LEDs (one red/green LED and eight red LEDs) are visi-
ble through the faceplate. The HSS module occupies one slot in
an INFI 90
®
module mounting unit.
HSS MODULE APPLICATION
The HSS module interfaces a processor module to a servo valve
or I/H converter, providing control (manual or automatic) of a
hydraulic actuator. The hydraulic actuator positions a gas tur-
bine fuel valve or steam governor valve. As the fuel or steam
valve opens or closes, it regulates fuel or steam flow to the tur-
bine, thus controlling the turbine speed. Figure
shows an
example of the HSS module within the INFI 90 hierarchy.
In most applications, the HSS module works with the fre-
quency counter (FCS) module through a multi-function proces-
sor (MFP) module. The FCS module counts and times pulse
inputs from a magnetic sensing device on the turbine shaft.
