ABB IMHSS03 Hydraulic Servo Module
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 1-1 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.

The MFP module uses the data from the FCS module to calcu late turbine speed. The configuration within the MFP module
uses the calculated speed to drive the servo valve outputs
according to the control strategy.
FEATURES
Enhancements to the IMHSS03 module improve its perfor mance over its predecessor, the IMHSS01 and IMHSS02 mod ules. Performance improvements include:
• High resolution analog-to-digital and digital-to-analog con verters, more accurate LVDT signal condition, an I/H con verter interface, and improved digital and analog input/
output isolation.
• The IMHSS03 module can automatically tune its demodu lator gain, offering better control loop response.
• The redundant LVDT interface can handle AC or DC LVDT
transformers.
• Redundant servo valve outputs offer the choice of operating
two active controlling servo valves simultaneously or one
active controlling servo valve with one servo valve instandby.
INSTRUCTION CONTENT
This instruction contains nine sections and five appendices.
Read this document before installing or operating the HSS
module. A summary of section content follows.
Introduction Contains general information and technical specifications.
Description andOperation
Uses block diagrams, schematics and text to explain moduleoperation.
Installation Covers the preliminary steps to prepare the module for opera tion. It covers switch settings, configuration and field wiring.
Calibration Explains how to calibrate the module and LVDT transformer,
and tune the control loop before placing it into operation.
Operating Procedures Provides information on daily use, start-up procedures and
normal operation.
Troubleshooting Explains LED conditions, lists status messages and lists cor rective action if problemsoccur.
Maintenance Contains scheduled maintenance tasks and procedures.
Repair/ReplacementProcedures
Contains procedures that explain how to replace the module,
and termination unit and module. It also has a spare parts list
with Bailey part numbers for related parts, cables, and fuses.
Support Services Explains the services and training that Bailey makes availableto their customers.
Appendices Provide a quick reference of HSS module dipswitch settings,
explain calibration procedures using function code 150, and
termination unit/module dipshunt and jumper settings.