The IS400TCASH1A is an important component of the PCAA (Core Analog I/O Pack) within the GE Mark VIe control system. Specifically, it belongs to the TCAS terminal board type. As part of the PCAA module, this terminal board provides customer terminals and signal routing, accurately and reliably transmitting analog signals from field devices to the BCAA and BCAB analog processing boards.
The IS400TCASH1A plays a critical role in gas turbine control systems. It handles a large number of analog signal input/output tasks, including thermocouple signals, 4-20 mA current loop signals, LVDT (Linear Variable Differential Transformer) excitation and feedback signals, servo coil drive signals, pulse rate inputs, and more. This terminal board can be applied in simplex and TMR (Triple Modular Redundant) systems, meeting the reliability, availability, and safety requirements of various industrial applications.
As part of the PCAA module, which is the least replaceable unit (LRU), the IS400TCASH1A works together with the BCAA main board, the BCAB interface board, and the BPPx processor board to form the complete PCAA core analog I/O assembly. The module receives 28 V dc control power through the P5 connector and supplies 28 V dc power through the P4 connector to the JGPA terminal board for field cable shield termination. Additionally, the IS400TCASH1A connects to the TCAT terminal board via two 68-pin cable connectors (P1 and P2) to achieve signal fan-out, distributing a single field signal to one or three PCAA modules.
II. Hardware Features and Structure
2.1 Physical Structure and Connectors
As the terminal board of the PCAA module, the IS400TCASH1A integrates multiple connector interfaces to ensure stable connections with external devices and other boards:
P5 Power Connector: 3-pin power interface for inputting 28 V dc power to power the entire PCAA module and terminal board. Note that the module receives power directly from the P5 connector, not through the normal power connector on the processor board.
P4 Power Output Connector: Provides 28 V dc power to the JGPA terminal board for field cable shield grounding.
P1 and P2 Connectors: Both are 68-pin cable connectors for connecting to the TCAT terminal board. These two connectors support signal fan-out, distributing signals from field devices to one or three PCAA modules, enabling simplex or TMR system configurations.
ENET1 and ENET2 Ethernet Interfaces: Two RJ-45 Ethernet connectors, serving as the primary system interface and the redundant/secondary system interface, respectively, for connection to the IONet network, enabling data communication between the controller and the module.
Euro Style Box-Type Terminal Blocks: The IS400TCASH1A is equipped with 120 pluggable Euro style box-type terminals for field device signal wiring. These terminals support various conductor types and cross-sections, facilitating field installation and maintenance.
2.2 Terminal Wiring Characteristics
The Euro style box terminals of the IS400TCASH1A support the following conductor specifications:
Conductor Type | Minimum Cross-section | Maximum Cross-section |
Solid conductor | 0.2 mm² | 2.5 mm² |
Stranded conductor | 0.2 mm² | 2.5 mm² |
Stranded conductor with ferrule and plastic sleeve | 0.25 mm² | 2.5 mm² |
Stranded conductor with ferrule without plastic sleeve | 0.25 mm² | 2.0 mm² |
AWG specification | 24 AWG | 12 AWG |
2.3 Module Design Philosophy
The PCAA module (including the IS400TCASH1A terminal board) consists of four separate circuit boards in a single physical assembly. Because it is difficult to isolate a failure to a single board, the entire module is considered the least replaceable unit. Therefore, field diagnosis or replacement of individual circuit boards within the module is not permitted. If the module fails, the entire PCAA module must be replaced.
III. Signal Types and I/O Allocation
The IS400TCASH1A terminal board provides extensive signal access capabilities, covering various analog signal types required for gas turbine control. Based on the division of signals between PCAA terminals and TCAT terminals, the IS400TCASH1A is primarily responsible for the following signals:
3.1 PCAA Terminal Signals (Wired Directly to IS400TCASH1A)
Number of Signals | Signal Type | Screws per Signal |
25 | Thermocouple inputs | 2 |
10 | Analog 4-20 mA inputs | 2 |
2 | Analog 4-20 mA or ±10 V inputs | 2 |
2 | Analog 4-20 mA outputs | 2 |
1 | ±12 V power output | 2 |
6 | LVDT excitation outputs | 2 |
6 | Servo coil driver outputs | 2 |
3 | Common connections | 1 |
2 | TTL pulse inputs | 2 (with power) |
3.2 TCAT Terminal Signals (Fanned to IS400TCASH1A via TCAT)
Number of Signals | Signal Type | Screws per Signal |
12 | Fanned seismic inputs | 2 |
24 | Fanned analog 4-20 mA inputs | 2 |
12 | 24 V output power at 25 mA | 2 |
3 | Voting 4-20 mA outputs | 2 |
12 | Fanned LVDT feedback | 2 |
2 | Fanned magnetic pulse rate inputs (servo flow meter) | 2 |
1 | Servo suicide relay input | 2 |
V. Configuration and Operation
4.1 Analog Input Configuration
The IS400TCASH1A supports interfaces to various types of 4-20 mA transmitters. Each analog input terminal has a jumper next to it to select whether the return terminal is grounded or floating (default position is floating/open). For analog inputs 11 and 12, an additional jumper is provided to remove the 250 Ω burden resistor, allowing ±10 V dc voltage input application.
The associated JGPA board provides twelve 24 V dc output terminals, one for each 4-20 mA transmitter input.
4.2 Servo Output Configuration
The IS400TCASH1A supports six servo outputs, each configurable via jumpers for TMR mode (3-coil servo) or simplex mode (2-coil servo). The first two servo outputs are also equipped with an external suicide function via the SVRL1 and SVRL2 terminals. When an external contact closes across these terminals, the servo output is isolated from the digital regulator control, providing a direct connection through a current limiting resistor (15 mA fixed output) for control protective response.
4.3 LVDT Position Servo System
The IS400TCASH1A receives secondary-side signals from LVDT sensors via the TCAT terminal board. These signals are conditioned by the BCAA acquisition board, converted to a dc equivalent signal, and read by the processor through A/D converters. The PCAA firmware can run up to six independent digital servo regulators, each loop operating at a 100 Hz sample rate. The regulator output is written to a D/A converter, which then provides the current command for the analog current regulator.
4.4 Calibration Function
When a new terminal board is used on a system, calibration of LVDTs associated with PSVO, PSVP, PCAA, or PMVE (MVRA or MVRF) servos is required. The controller saves the barcode of the terminal board and compares it to the current terminal board during reconfiguration load time. Each time a calibration is saved, it updates the barcode name to the current board.
V. Diagnostics and Alarms
As part of the PCAA module, the IS400TCASH1A provides comprehensive self-diagnostic functions. When a diagnostic detects an anomaly, the system generates corresponding alarms. The following are common alarms related to the IS400TCASH1A:
Alarm Code | Description | Possible Cause | Solution |
33-67 | Thermocouple Unhealthy | Millivolt input exceeds thermocouple range; wrong TC type configured; open wire; stray voltage or noise causing input to exceed -63 mV | Check field wiring and shielding; check TC for open circuit; measure millivolt signal; verify TC type matches configuration |
68 | Cold Junction Unhealthy, Using Backup | Local cold junction signal from TCAS terminal board out of range (normal: -50 to 85°C) | If hardware is within normal temperature range, possible cold junction sensor failure; replace PCAA module |
69-80 | TCAS Analog Input Unhealthy | Wrong or missing excitation to transducer; faulty transducer; jumper settings mismatch configuration; input out of range; open or short circuit | Check field wiring; check field device; check ground select jumper; verify input within 3.0-21.5 mA, ±5.25 V, ±10.5 V range |
117-122 | LVDT Excitation Failed | Excitation ground fault; field wiring issue or LVDT sensor failure; internal hardware failure | Check field wiring and shielding for LVDT excitation; check LVDT sensor; if hardware failure, replace PCAA |
123-134 | LVDT Excitation Voltage Out of Range | Actual LVDT excitation exceeds ±10% of ExcitMonCal; possible terminal board failure | Measure excitation voltage and compare with configuration parameter; check LVDT sensor; recalibrate servo; replace PCAA |
135-146 | LVDT Position Out of Limit | LVDT excitation issue; faulty transducer; open or short circuit; input out of range; not calibrated | Check field wiring and excitation; check LVDT sensor; calibrate servo regulator; verify MinVrms and MaxVrms limits; verify ExcitSelect matches wiring |
155-160 | Servo Disabled: Configuration Error | Servo position input connected to unused LVDT; flow input to unused PR; pressure input to unused analog input; incorrect configuration parameters | Check and correct configuration parameters; verify regulator inputs connected to enabled sensors; use ToolboxST advanced diagnostics for error list |
161-166 | Servo Output Suicide Active | Feedback out of range; current feedback mismatch with command; incorrect input connections | Check configuration; verify inputs connected to used sensors; check position sensor connections and mechanical integrity; check servo output loop wiring for open or short |
217 | TCAT Configuration and Hardware Mismatch | TCAT configured in ToolboxST but not connected; TCAT not configured but connected | Verify ToolboxST TCAT selection matches actual hardware; verify P1 and P2 cables not swapped; ensure cables tightened and terminal boards grounded; perform power-down reset |
218 | TCAT Connector P1 and P2 Types Mismatch | P1 and P2 connection types (R/R, S/S, T/T) do not match | Check ToolboxST configuration and P1/P2 cable connections between TCAS and TCAT to ensure type matching |
VI. Installation and Operation Key Points
6.1 Installation Steps
Securely mount the PCAA module.
Connect the JGPA power connection to the P4 connector on the PCAA.
Connect the PCAA module to an optional associated TCAT terminal board using two 68-pin cables on connectors P1 and P2. Finger-tighten only the cable mounting screws into the PCAA and TCAT to ensure proper cable grounding. Failure to secure the cables may result in inability of the PCAA to read the electronic ID on the TCAT and may reduce signal quality.
Plug in one or two Ethernet cables depending on system configuration. When a single IONet connection is used, the module operates correctly over either port. If dual connections are used, standard practice is to connect ENET1 to the network associated with the R controller.
Check grounding of the JGPA shield wire terminals. In most applications, JGPA shield ground terminals are electrically tied to the sheet metal the board is mounted on. In some applications requiring independent shield ground, provide a suitable ground wire between one or more JGPA terminals and the required shield ground potential.
Apply power to the module through the P5 connector and check the power and Ethernet status indicator lights.
Use the ToolboxST application to configure the PCAA as necessary.
6.2 Important Notes
Power Note: The module operates from a power source applied directly to the module P5 connector, not through the normal power connector located on the processor board.
Cable Removal Note: When removing 68-pin cables, ensure that the hex posts in the board-mounted connectors do not turn when backing out the cable thumbscrews.
Grounding Note: The 68-pin cables must be properly grounded; otherwise, electronic ID reading and signal quality may be affected.
Configuration Note: Do not change the ThermCplUnit parameter in ToolboxST arbitrarily, as this affects the engineering units seen by the application code and may affect external devices such as HMIs and Historians.
