The IS200TSVCH1A is a core interface component of the servo control subsystem within the General Electric (GE) Mark VIe control system. As a Servo Input/Output Terminal Board (TSVC), the IS200TSVCH1A is specifically designed to interface with the PSVO I/O processor pack and the WSVO servo driver, providing bidirectional current drive for electro-hydraulic servo valves on steam and gas turbines, while simultaneously acquiring position feedback signals from Linear Variable Differential Transformers (LVDT) or Linear Variable Differential Reluctance (LVDR) sensors. The board supports both simplex and Triple Modular Redundant (TMR) configurations, meeting control requirements ranging from simple to the most critical steam turbine admission valves and gas turbine fuel valves.
The core feature of the TSVCH1 version is its four onboard isolation transformers (T1 through T4), which provide transformer-isolated excitation power for LVDT/LVDR position sensors. This galvanic isolation design effectively suppresses common-mode noise and ground loop interference, ensuring high accuracy and long-term stability of the position feedback signals. The IS200TSVCH1A can simultaneously handle up to 8 LVDT position feedback signals and 2 pulse rate flow signals, and outputs 2 servo valve control currents (each capable of driving up to 3 coils), comprehensively covering the precision servo control requirements of steam valves and fuel valves in large power generation units.
System Architecture and Key Features
The IS200TSVCH1A works in coordination with the PSVO I/O pack and the WSVO servo driver inside the control cabinet. The three control sections (R, S, and T) correspond to three PSVOs and three WSVOs respectively, connected via the J1 connectors (to PSVO) and J2 connectors (to WSVO) on the board for plug-and-play integration. The board provides independent 28 V DC power inputs for each section (via connector J28). The power supplies for the three sections are mutually isolated on the board and can be manually enabled or disabled independently using switches SW1, SW2, and SW3, supporting online maintenance.
In a TMR configuration, each servo output can drive three independent coils, enabling hardware-level 2-out-of-3 voting output. Even if a single coil fails, the remaining two coils can still maintain the normal control force of the valve. The board also features an emergency trip interface (JD1 or JD2) for receiving an external trip signal from the Protection Module (PPRO). Under abnormal conditions such as emergency overspeed, this forces the valve closed, serving as the ultimate safety backup for the servo amplifier.
Another notable feature of the TSVCH1 is the "suicide relay" within the servo output channel. Under firmware control, when the valve position exceeds its safety limits, this relay shorts the PSVO output signal to signal common, rapidly reducing the servo current to zero. The valve then returns to its safe position under spring or hydraulic force. This state requires a manual reset command to clear, ensuring the system will not accidentally recover before the fault is confirmed and addressed.
Detailed Core Functions
1. Servo Output Channels
The IS200TSVCH1A provides two fully independent bidirectional servo current output channels, each configurable as:
The servo current range is selected via onboard jumpers, supporting multiple standard steps of ±10 mA, ±20 mA, ±40 mA, ±80 mA, and ±120 mA, as well as non-standard combinations. The jumpers simultaneously set the corresponding internal current-limiting resistor, ensuring the WSVO driver has sufficient dynamic voltage margin across various coil impedances. The board supports servo cable lengths of up to 300 meters (984 feet), with a maximum total two-way cable resistance of 15 Ω, meeting the decentralized layout needs of large units.
2. LVDT Position Feedback
The IS200TSVCH1A can accept up to 8 channels of LVDT or LVDR position sensor signals. Each servo control loop can be configured with 1, 2, 3, or 4 LVDT sensors, achieving single, dual, triple, or quadruple redundant feedback. The TSVCH1 provides 7 V rms, 3.2 kHz excitation power for the LVDTs through the four isolation transformers T1 to T4, with total harmonic distortion of less than 1%. The isolated design completely separates the sensor circuit from the control electronics, effectively reducing common-mode interference.
The LVDT AC output signal (typically 0.7 V rms at zero position and 3.5 V rms at full stroke) is converted to a DC signal on the board, conditioned through a low-pass filter, and sent to the PSVO I/O pack for A/D conversion via the DC-37 connector. Each feedback channel features both a hardware high/low limit check and a configurable software system limit check. In a redundant sensor configuration, if one sensor fails, the control system automatically excludes it from the feedback calculation and switches to the healthy sensor, achieving uninterrupted operation.
3. Pulse Rate Inputs
The IS200TSVCH1A provides two pulse rate input channels, compatible with both passive magnetic pickups and active pulse rate transducers (TTL type) interchangeably without hardware configuration. These two inputs are typically used for liquid fuel flow measurement and flow divider feedback monitoring in gas turbine applications, and are generally not used in steam turbine applications.
The pulse rate inputs can monitor a frequency range of 2 Hz to 12 kHz. The three 28 V DC power supplies introduced via connector J28 are diode high-selected and current-limited on the board to provide 24 V DC excitation for active probes. The input signals are sampled and processed in the PSVO I/O pack at a rate of 10 ms or 20 ms. Cable lengths of up to 300 meters are supported, with shielded twisted-pair cable recommended.
4. Safety and Redundancy Features
The IS200TSVCH1A integrates multiple safety guarantees:
Emergency Trip: An external trip signal from the PPRO protection module is connected to connector JD1 or JD2. In simplex applications, the trip signal directly controls relay K1 on the board, disconnecting the servo output and applying a bias to force the valve closed. This function is only active when the servo coils are driven from the R section, and it is essential to verify that switch SW1 is in the ON position and the green DS1 LED is illuminated, indicating that P28T power is available for the K1 circuit.
TMR Output Voting: In a TMR system, the three coils of each servo channel are driven independently. A single driver failure does not affect the overall control force on the valve. Meanwhile, the PSVO I/O pack monitors the servo current and LVDT feedback signal of each channel in real time, issuing a diagnostic alarm if a limit is exceeded.
Online Maintenance: The three 28 V power feeds are independently controlled by switches SW1, SW2, and SW3. When a PSVO or WSVO in a specific section needs to be replaced, only the power switch for that corresponding channel needs to be turned off. The component can then be safely removed while the remaining channels continue to maintain servo control, without requiring a shutdown.
5. Configuration and Diagnostics
Hardware configuration of the IS200TSVCH1A is mainly accomplished via jumpers. In simplex applications, the coil current for Servo 1 is selected by JP1, and for Servo 2 by JP2. In TMR applications, the three coil currents for Servo 1 are selected by JP1, JP3, and JP5, and the three channels for Servo 2 by JP2, JP4, and JP6. Additionally, the board features three power switches (SW1-SW3) and corresponding LED indicators (P28R, P28S, P28T status). All other servo parameters (such as nominal current, number of paralleled coils, number of LVDT sensors, filter times, etc.) are configured in the PSVO I/O pack through the ToolboxST application.
The IS200TSVCH1A, working with the PSVO I/O pack, provides comprehensive diagnostic coverage:
Servo current out of limits or not responding fault.
LVDT feedback signal out of limits fault (latchable).
Board ID chip mismatch fault (prevents incorrect board replacement).
Automatic reading of the ID chip on each connector, verifying board type, serial number, and revision.
All diagnostic information can be viewed and reset in detail through ToolboxST, facilitating rapid fault location and resolution.
Application Scenarios
The IS200TSVCH1A is primarily applied in the precision servo control of the following large rotating machinery:
Steam turbine main steam admission valve position control.
Steam turbine reheat steam admission valve control.
Gas turbine fuel control valve control (gas or liquid fuel).
Feedwater pump turbine governor valve control.
Compressor inlet guide vane and anti-surge valve position control.
Any electro-hydraulic servo system requiring high reliability, high precision, and long-distance cable drive.
In a TMR configuration, a single IS200TSVCH1A fully meets the redundant control requirements of critical valves, providing a solid guarantee for the safe and stable operation of power generation units. In simplex applications, its compact size and rich functionality can also deliver high-performance servo control for smaller units or auxiliary systems.
