DESCRIPTION AND OPERATION
CONTROL LOOP OPERATION
I-E96-322A
2 - 3
differential voltage into actuator position feedback. The HSS
module is self-checking and notifies the MFP module if a fail-
ure occurs.
The HSS module initiates manual control of the turbine throt-
tle valve if an HSS module communication failure with the MFP
module occurs (or the MFP module goes into configuration
mode). The HSS module provides inputs that the user hard
wires to a 24 VDC source. The user directs the HSS module to
raise or lower the actuator through external inputs (pushbut-
tons, contacts, etc.). Also, a trip bias circuit on the HSS module
drives the fuel throttle valve to the closed position if necessary.
FCS Module
The FCS module detects turbine speed by counting pulses it
receives from a magnetic pickup on the turbine shaft. Addition-
ally, it keeps a 24-bit timer value corresponding to the period of
the pulse count. It stores these values in a buffer and sets a
data available status bit to notify the MFP module that it has
current data. FCS module operation is automatic; it continu-
ously updates the count and holds it for the MFP module.
For the MFP module to work with the FCS module, it requires
function code 145 in its configuration. Function code 145
defines the module address, high/low speed alarms and high/
low rate of change alarms. The block output is frequency of
input pulses in hertz. The frequency counter continuously
checks itself and notifies the MFP module if a failure occurs.
MFP Module
The MFP module is the controlling module of the control loop
and controls turbine speed according to the control strategy of
the user. The MFP module requests data from the FCS module
to calculate turbine speed. If the FCS module has data avail-
able, it sends it to the MFP module. If there is no data available
the MFP module must make another request. If the turbine
speed goes above or below the speed set point in the MFP mod-
ule configuration, the MFP module will send a position demand
to the HSS module to adjust the throttle valve. This process
repeats continuously at the cycle time of the MFP module.
The user sets the turbine speed limits and high/low speed
alarms during configuration of the MFP module and I/O mod-
ules. Additionally, the user calibrates the hydraulic actuator
and LVDT transformer. The user also initiates auto tuning of
the demodulator gain. Proportional gain is tuned manually
(demodulator gain can also be tuned manually). The MFP mod-
ule sends data, module status and alarms to the operator
interface during normal operation. The operator can monitor
system operation and initiate automatic or manual control
through the operator interface.
