Speedtronic Mark VI control system configuration part 2
Note: In Part 2, Human Machine interface, power supplies, communications etc is discussed

Operator Interface
The operator interface is commonly referred to as the Human Machine Interface (HMI). It is a PC with

  • a Microsoft® Windows NT® operating system supporting client/server capability,
  • a CIMPLICITY® graphics display system, 
  • a Control System Toolbox for maintenance, and 
  • a software interface for the Mark VI and other control systems on the network.

It can be applied as:

  • The primary operator interface for one or multiple units, 
  • A backup operator interface to the plant DCS operator interface,
  • A gateway for communication links to other control systems,
  • A permanent or temporary maintenance station, 
  • An engineer’s workstation

All control and protection is resident in the Mark VI control, which allows the HMI to be a non-essential component of the control system. It can be reinitialized or replaced with the process running with no impact on the control system. The HMI communicates with the main processor card in the Control Module via the Ethernet based Unit Data Highway (UDH). All analog and digital data in the Mark VI is accessible for HMI screens including the high resolution time tags for alarms and events. System (process) alarms and diagnostics alarms for fault conditions are time tagged at frame rate (10/20/40 ms) in the Mark VI control and transmitted to the HMI alarm management system.

System events are time tagged at frame rate, and Sequence of Events (SOE) for contact inputs are time tagged at 1ms on the contact input card in the Control Module. Alarms can be sorted according to ID, Resource, Device, Time, and Priority. Operators can add comments to alarm messages or link specific alarm messages to supporting graphics.

Software Maintenance Tools

The Mark VI is a fully programmable control system. Application software is created from inhouse software automation tools which select proven GE control and protection algorithms and integrate them with the I/O, sequencing, and displays for each application. A library of software is provided with general-purpose blocks, math blocks, macros, and application specific blocks. It uses 32-bit floating point data (IEEE-854) in a QNX operating system with real-time applications, multitasking, priority-driven preemptive scheduling, and fast context switching.

Application software is executed sequentially and represented in its dynamic state in a ladder diagram format. Maintenance personnel can add, delete, or change analog loops, sequencing logic, tuning constants, etc. Data points can be selected and “dragged” on the screen from one block to another to simplify editing. Other features include logic forcing, analog forcing, and trending at frame rate.


Communications are provided for internal data transfer within a single Mark VI control; communications between Mark VI controls and peer GE control systems; and external communications to remote systems such as a plant distributed control system (DCS). The Unit Data Highway (UDH) is an Ethernet based LAN with peer-to-peer communication between Mark VI controls, EX2000 Generator Excitation Controls, Static Starters, the GE Fanuc family of PLC based controls, HMIs, and Historians. The network uses Ethernet Global Data (EGD) which is a message-based protocol with support for sharing information with multiple nodes based on the UDP/IP standard (RFC 768).

The UDH communication driver is located on the Main Processor Card in the Mark VI. This is the same card that executes the turbine application software; therefore, there are no potential communication failure points between the main turbine processor and other controls or monitoring systems on the UDH. In TMR systems, there are three separate processor cards executing identical application software from identical databases. Two of the UDH drivers are normally connected to one switch, and the other UDH driver is connected to the other switch in a star configuration. Network topologies conform to Ethernet IEEE 802.3 standards.

Communication link options include:

  • An RS-232 port with Modbus Slave RTU or ASCII communications from the Main Processor Card. (Simplex: full capability. TMR: monitor data only no commands)
  • An RS-232 port with Modbus Master /Slave RTU protocol is available from the HMI.
  • An RS-232/485 converter (halfduplex) can be supplied to convert the RS-232 link for a multi-drop network.
  • Modbus protocol can be supplied on an Ethernet physical layer with TCP-IP for faster communication rates from the HMI.
  • Ethernet TCP-IP can be supplied with a GSM application layer to support the transmission of the local high resolution time tags in the control to a DCS from the HMI. This link offers spontaneous transmission of alarms and events, and common request messages that can be sent to the HMI including control commands and alarm queue commands. Typical commands include momentary logical commands and analog “set-point target” commands. Alarm queue commands consist of silence (plant alarm horn) and reset commands as well as alarm dump requests that cause the entire alarm queue to be transmitted from the Mark VI to the DCS. 
  • Additional “master” communication drivers are available from the HMI.

Time Synchronization

Time synchronization is available to synchronize all controls and HMIs on the UDH to a Global Time Source (GTS). Typical GTSs are Global Positioning Satellite (GPS) receivers such as the StarTime GPS Clock or other time processing hardware. The preferred time sources are Universal Time Coordinated (UTC) or GPS; however, the time synchronization option also supports a GTS using local time as its base time reference. The GTS supplies a time-link network to one or more HMIs with a time/frequency processor board.


Each circuit card in the Control Module contains system (software) limit checking, high/low (hardware) limit checking, and comprehensive diagnostics for abnormal hardware conditions. System limit checking consists of 2 limits for every analog input signal, which can be set in engineering units for high/high, high/low, or low/low with the I/O Configurator. In addition, each input limit can be set for latching/nonlatching and enable/disable. Logic outputs from system limit checking are generated per frame and are available in the database (signal space) for use in control sequencing and alarm messages.

High/low (hardware) limit checking is provided on each analog input with typically 2 occurrences required before initiating an alarm. These limits are not configurable, and they are selected to be outside the normal control requirements range but inside the linear hardware operational range (before the hardware reaches saturation). Diagnostic messages for hardware limit checks and all other hardware diagnostics for the card can be accessed with the software maintenance tools (Control System Toolbox).

Hardware diagnostic alarms are displayed on the yellow “status” LED on the card front. Each card front includes 3 LEDs and a reset at the top of the card along with serial and parallel ports. The LEDs include: RUN: Green; FAIL: Red; STATUS: Yellow.

Each circuit card and termination board in the system contains a serial number, board type, and hardware revision that can be displayed; 37 pin “D” type connector cables are used to interface between the Termination Boards and the J3 and J4 connectors on the bottom of the Control Module. Each connector comes with latching fasteners and a unique label identifying the correct termination point. One wire in each connector is dedicated to transmitting an identification message with a bar-code serial number, board type, hardware revision, and a connection location to the corresponding I/O card in the Control Module.

In many applications, the control cabinet is powered from a 125Vdc battery system and short circuit protected external to the control. Both sides of the floating 125Vdc bus are continuously monitored with respect to ground, and a diagnostic alarm is initiated if a ground is detected on either side of the 125Vdc source. When a 120/240vac source is used, a power converter isolates the source with an isolation transformer and rectifies it to 125Vdc. A diode high select circuit chooses the highest of the 125Vdc busses to distribute to the Power Distribution Module. A second 120/240vac source can be provided for redundancy.
Diagnostics produce an under-voltage alarm if either of the AC sources drop below the undervoltage setting. For gas turbine applications, a separate 120/240vac source is required for the ignition transformers with short circuit protection of 20A or less.

The resultant “internal” 125Vdc is fuse-isolated in the Mark VI power distribution module and fed to the internal power supplies for the Control Modules, any expansion modules, and the termination boards for its field contact inputs and field solenoids. Additional 3.2A fuse protection is provided on the termination board TRLY for each solenoid. Separate 120Vac feeds are provided from the motor control center for any AC solenoids and ignition transformers on gas turbines.

Go back to Mark VI configuration Part 1

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