The TBAIH1C Analog Input/Output Terminal Board is a critical interface component within General Electric's (GE) Mark VI and Mark Vle gas and steam turbine control systems. As a member of the TBAI family, the TBAIH1C is designed for high-reliability, high-precision industrial process signal acquisition and control. Operating in harsh industrial environments, this board is responsible for safely and accurately transmitting analog signals from various field sensors (transmitters) to the control system processors, while simultaneously converting digital commands from the controllers into standard analog current signals to drive field actuators. It serves as the essential "bridge" connecting the control system to field devices.
The core design philosophy of the TBAIH1C centers on flexibility, high reliability, and robust diagnostic capabilities. It offers extensive support for various signal interface types and can be easily adapted to different application needs through simple jumper configuration. Its built-in noise suppression, surge protection, and redundant power supply design ensure signal stability and system safety in environments with strong electromagnetic interference and in safety-critical applications. Whether used for simple Simplex control loops or in extremely demanding Triple Modular Redundant (TMR) safety-critical systems, the TBAIH1C delivers exceptional performance.
II. Key Features and Functionality
High-Density Analog Channels: A single board integrates 10 Analog Input (AI) channels and 2 Analog Output (AO) channels, providing ample signal processing capability in a compact footprint, helping to reduce cabinet space and system complexity.
Comprehensive Input Signal Compatibility: The 10 analog input channels offer high flexibility and can be easily configured via jumpers to support multiple signal sources without hardware changes:
Current Input: Standard 4-20 mA two-wire, three-wire, and four-wire transmitters.
Voltage Input: ±5 V DC or ±10 V DC voltage signals.
Special Current Input: Two channels (Channels 9, 10) can be configured for ±1 mA low-level current signal input.
Flexible Powering Options: Supports transmitters powered by the board's internal 24V DC supply (providing loop power for two-wire and three-wire transmitters) or by an external independent power source.
Configurable High-Drive Outputs: Both analog output channels support 0-20 mA current output. One channel (Output 1) can be configured via a jumper for 0-200 mA high-current output mode to drive special high-load actuators. The output circuits feature comprehensive protection.
Robust Noise Immunity and Protection:
Noise Suppression Circuits: Each input and output channel is equipped with dedicated noise suppression circuitry to effectively filter high-frequency noise.
Surge Protection: Designed to withstand voltage surges common in industrial environments, protecting downstream I/O processors and the core control system.
High Common-Mode Rejection Ratio (CMRR): AC CMRR is 60 dB, and DC CMRR is as high as 80 dB, ensuring accurate signal measurement even in environments with significant ground potential differences or noise.
Support for Full Redundant Architecture (TMR):
The TBAIH1C board features three standard DC-37 pin connectors (JR1, JS1, JT1) on its front, designed specifically for Triple Modular Redundant systems.
In TMR applications, input signals are "fanned out" to the three independent control channels (R, S, T).
Analog outputs employ a "Mid-value Voting" mechanism: All three control channels generate their output currents, which are summed on the TBAIH1C board. The total current is measured via a shunt resistor and fed back to each controller. The final output current is the median value of the three controller outputs, thereby masking a single channel failure and significantly enhancing output loop reliability.
The 24V DC power for transmitters is sourced from all three controllers and is diode-OR shared on the board, ensuring field instrument power is not affected by a single controller power supply failure.
Compatibility with Multiple Control System Generations:
Mark VI Systems: Connected via cables to VAIC I/O processor boards. Supports Simplex (connecting to one VAIC) or TMR (connecting to three VAICs) configuration.
Mark Vle Systems: The PAIC I/O pack plugs directly into the board connectors. Supports Simplex (one PAIC) or TMR (three PAICs) configuration. This direct plug-in design simplifies installation and maintenance.
Convenient Installation and Maintenance:
Utilizes pluggable barrier-type terminal blocks with 24 terminals each, accepting wires up to #12 AWG. For maintenance, the entire terminal block can be unplugged from the board, facilitating wiring and replacement without direct manipulation of the board.
A dedicated shield terminal attachment point is located adjacent to each terminal block, enabling proper single-point grounding for optimal Electromagnetic Compatibility (EMC).
Comprehensive On-Board Diagnostics and Hardware Identification:
Output Current Monitoring: Real-time monitoring of actual output current by measuring the voltage drop across a series resistor. The I/O processor generates a diagnostic alarm if an output becomes unhealthy.
Hardware ID Recognition: Each connector (JR1, JS1, JT1) has a read-only ID chip storing the terminal board's serial number, board type, revision number, and connector location. The I/O controller reads this ID at startup. If a board type mismatch, incorrect revision, or wrong connection location is detected, an immediate "hardware incompatibility" fault is generated, preventing system issues from misconfiguration.
"Suicide" Relay Protection: In the event of a severe output channel fault that cannot be cleared by a processor command, a "suicide" relay within the I/O controller activates, forcibly disconnecting the faulty output channel to prevent danger to field equipment.
III. Hardware Design and Interface Details
The TBAIH1C's hardware design embodies modularity and user-friendliness.
Terminal Blocks: Two independent terminal blocks correspond to input and output signals respectively. Clearly labeled, they support various wire gauges.
Configuration Jumper Area: Located centrally on the board, it is the core for functional configuration.
J1A-J8A: Input Type Selection for channels 1-8 (Current Input / Voltage Input).
J1B-J8B: Return Path Selection for channels 1-8 (Connected to common PCOM / Left Open).
J9A, J10A: Input Range Selection for channels 9, 10 (1 mA / 20 mA).
J9B, J10B: Return Path Selection for channels 9, 10.
J0: Output 1 Range Selection (20 mA / 200 mA).
System Connectors: The three DC-37 pin connectors are the data and power pathways between the TBAIH1C and the upper-level controllers. All three are used in TMR systems, while typically only JR1 is used in Simplex systems.
IV. Input/Output Configuration Guidelines
Users must correctly set the jumpers according to the specific model and wiring of the field sensors and actuators.
Two-Wire Transmitter (4-20mA): Set jumper J#A to "20mA", J#B to "Open". The board provides 24V power to the transmitter and receives the current signal over the same pair of wires.
Three-Wire Transmitter (4-20mA): Set jumper J#A to "20mA", J#B to "Open". Connect the transmitter's power positive, signal positive, and common (negative) terminals separately.
Four-Wire Transmitter (4-20mA): Set jumper J#A to "20mA", J#B to "Open". The transmitter is powered by a completely independent supply; only the signal wires connect to the TBAIH1C.
Externally Powered Transmitter (Voltage or Current): Set J#A to the corresponding position based on the signal type (voltage to "Vdc", current to "20ma"). J#B is typically set to "Open".
Voltage Input (±5/±10V): Set jumper J#A to "Vdc". Connect the signal wire to the corresponding channel's "Vdc" terminal.
Analog Output Configuration: Output 2 is fixed at 0-20mA. Output 1 is selected via the J0 jumper for either 0-20mA or 0-200mA.
V. Application in Triple Modular Redundant (TMR) Systems
In TMR systems, the TBAIH1C plays a vital role. It is not only a signal interface but also the key hardware for implementing output redundancy voting.
Input Side: A single field signal is simultaneously sent to the three independent I/O controllers (VAIC or PAIC) - R, S, and T - achieving physical signal triplication.
Power Side: The 24V power supplies from the three controllers are paralleled on the board, isolated by diodes, to power field transmitters, forming a redundant power source.
Output Side: This is the core of TMR. All three controllers calculate and output their control currents. These three currents are combined on the physical wiring of the TBAIH1C to jointly drive the field load. Simultaneously, a sampling resistor on the board converts the total current into a voltage signal, fed back to each controller. Each controller compares its commanded output with the measured total output and votes (takes the median value), thereby achieving fault masking in the output loop. Even if one controller's output is completely wrong, as long as the other two are normal, the final output remains correct.
VI. Diagnostics and Maintenance
Maintenance for the TBAIH1C primarily focuses on preventive inspection and fault troubleshooting.
Periodic Inspection: Check for loose terminal connections, correct jumper settings, and secure connectors.
Utilize System Diagnostics: Pay close attention to diagnostic alarm messages from the control system. For output faults or hardware incompatibility alarms, inspect the corresponding output loop or verify the board/connector model as prompted.
Replacement Procedure: If board replacement is needed, first record all jumper positions and wiring diagrams. After powering down, disconnect the cable connectors and terminal blocks. After installing the new board, restore jumpers and wiring to their original state and ensure ID recognition passes.
