The IS400TCASH1AGD is a high‑performance terminal board belonging to the TCAS series within the GE Mark VIe control system. It is an integral part of the PCAA (Core Analog I/O Pack) and serves as the primary field wiring interface for analog signals. The IS400TCASH1AGD provides customer connection points and signal routing, enabling accurate and reliable transmission of a wide variety of analog signals from field devices – such as gas turbines, compressors, and other industrial rotating machinery – to the BCAA and BCAB analog processing boards inside the PCAA module.
The IS400TCASH1AGD handles a large portion of the analog signal I/O required to operate a gas turbine. It supports thermocouple inputs, 4‑20 mA current loop I/O, seismic inputs, LVDT (Linear Variable Differential Transformer) excitation and feedback, pulse rate inputs, and servo coil outputs. The terminal board can be applied in both simplex (single PCAA) and TMR (Triple Modular Redundant) (three PCAA modules) configurations, meeting the demanding requirements for high availability, reliability, and safety in industrial control applications.
The IS400TCASH1AGD receives 28 V dc control power through the P5 connector and supplies 28 V dc power to a JGPA terminal board through the P4 connector for field cable shield termination. It also connects to a 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. A single TCAT terminal board fans signal inputs to one or three connected PCAA modules, and the shield ground together with 24 V field power terminals on an adjacent JGPA board supplement the terminals on the PCAA and TCAT.
As part of the PCAA module – which is regarded as the least replaceable unit (LRU) – the IS400TCASH1AGD works together with the BCAA main board, the BCAB interface board, and the BPPx processor board. The module is not designed for replacement of individual boards; any failure requires replacement of the entire PCAA assembly. The IS400TCASH1AGD employs surface‑mount technology and Euro style pluggable box‑type terminal blocks, offering excellent resistance to vibration, temperature extremes, and electromagnetic interference, and operates reliably in harsh industrial environments.
II. Hardware Structure and Interfaces
2.1 Physical Dimensions and Mounting
The physical dimensions of the IS400TCASH1AGD are identical to other TCAS series modules:
Parameter | Value |
Height | 8.26 cm (3.25 inches) |
Width | 4.19 cm (1.65 inches) |
Depth | 12.1 cm (4.78 inches) |
Mounting Method | Securely mounted as part of the PCAA assembly; the PCAA module is directly mounted to a panel or rack. The module uses pluggable Euro style box‑type terminal blocks for easy field wiring. |
2.2 Main Connectors
The IS400TCASH1AGD is equipped with the following connectors:
Connector | Type | Description |
P5 | 3‑pin power connector | Input for 28 V dc power for the module and terminal boards. Note: The module operates from a power source applied directly to the P5 connector, not through the normal power connector located on the processor board. |
P4 | Power output connector | Provides 28 V dc power to a JGPA board located for wire shield termination. |
P1 / P2 | 68‑pin high‑density connectors | Connect to the TCAT terminal board for signal fan‑out (distributing one field signal to one or three PCAA modules in simplex or TMR). |
ENET1 / ENET2 | RJ‑45 Ethernet ports | Primary (ENET1) and redundant/secondary (ENET2) system interfaces for connection to the IONet network. |
120 Euro terminals | Pluggable box‑type terminal blocks | For field device signal wiring, supporting various conductor types and cross‑sections. |
2.3 Terminal Wiring Specifications
The Euro style box terminals on the IS400TCASH1AGD accept conductors with the following characteristics:
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 without plastic sleeve | 0.25 mm² | 2.0 mm² |
Stranded conductor with ferrule with plastic sleeve | 0.25 mm² | 2.5 mm² |
AWG specification | 24 AWG | 12 AWG |
Two conductors of same cross‑section, solid | 0.2 mm² | 1.0 mm² |
Two conductors of same cross‑section, stranded | 0.2 mm² | 1.5 mm² |
Two conductors, stranded, ferrules without plastic sleeve | 0.25 mm² | 1.0 mm² |
Two conductors, stranded, TWIN ferrules with plastic sleeve | 0.5 mm² | 1.5 mm² |
III. Signal Types and I/O Allocation
The IS400TCASH1AGD handles a comprehensive set of analog signals. Based on the signal split between PCAA terminals and TCAT terminals (as documented in GEH‑6721_Vol_III_BG), the signals wired directly to this terminal board and those fanned via TCAT are detailed below.
3.1 Signals Wired Directly to the IS400TCASH1AGD (PCAA Terminals)
Number of Signals | Signal Type | Screws per Signal |
25 | Thermocouple inputs (Types E, J, K, S, T supported) | 2 |
10 | Analog 4‑20 mA inputs | 2 |
2 | Analog 4‑20 mA or ±10 V configurable inputs | 2 |
2 | Analog 4‑20 mA outputs | 2 |
1 | ±12 V dc power output (50 mA rating) | 2 |
6 | LVDT excitation outputs (7 Vrms, 3.2 kHz, 60 mA drive) | 2 |
6 | Servo coil driver outputs (±10 mA) | 2 |
3 | Common connections (COM) | 1 |
2 | TTL pulse rate inputs (with sensor power) | 2 (including power) |
3.2 Signals Fanned via TCAT (Processed through the IS400TCASH1AGD)
Number of Signals | Signal Type | Screws per Signal |
12 | Fanned seismic inputs (velocity sensors) | 2 |
24 | Fanned analog 4‑20 mA inputs | 2 |
12 | 24 V output power at 25 mA each (for transmitters) | 2 |
3 | Voting 4‑20 mA outputs (for TMR configurations) | 2 |
12 | Fanned LVDT feedback signals | 2 |
2 | Fanned magnetic pulse rate inputs (servo flow meter) | 2 |
1 | Servo suicide relay input (for first two servo outputs) | 2 |
IV. Signal Accuracy Specifications
The following table lists the specified and typical accuracies for each signal type supported by the IS400TCASH1AGD.
Signal Type | Specified Accuracy (including all errors) | Typical Accuracy (at 25°C) |
Thermocouple inputs (Types E, J, K, S, T) | ±0.10% of full scale (-13.8 to +45.5 mV range) | ±0.06% |
Analog 4‑20 mA inputs (PCAA and TCAT) | ±0.25% | ±0.10% |
Analog 0‑10 V dc inputs | ±0.50% | ±0.20% |
Pulse rate inputs | ±0.05% of reading | — |
Flow rate inputs | ±0.05% of reading | — |
Seismic inputs (±1.5 V peak) | ±2.00% | ±0.90% |
LVDT inputs (0‑7.07 Vrms) | ±1.00% | ±0.25% |
LVDT excitation monitor inputs | ±1.00% | ±0.55% |
LVDT excitation output | 7 V ac RMS ±5.00% | ±3.00% (at 25°C) |
Servo driver output (±10 mA) | ±3.50% | ±0.70% |
Analog 4‑20 mA output (PCAA and TCAT) | ±0.75% | ±0.43% |
24 V power output (JGPA and TCAT) | 24 V dc ±0.5% over 0‑25 mA range | — |
V. Configuration and Operation
Each analog input channel on the IS400TCASH1AGD has a jumper (JP1 through JP12) adjacent to the terminals to select whether the return terminal is grounded (GND) or floating (OPEN). The default jumper position is floating/open. For analog inputs 11 and 12, additional jumpers (JP13, JP14) select between MA (4‑20 mA mode with 250 Ω burden resistor) and VOLT (±10 V voltage mode, burden resistor removed). The associated JGPA board provides twelve 24 V dc terminals, one for each 4‑20 mA transmitter input.
5.2 Servo Output Configuration
The six servo outputs can each be configured via jumpers (JP15 through JP20) as follows:
Jumper | Position 1‑2 (TMR) | Position 2‑3 (Simplex) |
JP15 | Servo 1 output select (3‑coil TMR) | Servo 1 output select (2‑coil simplex) |
JP16 | Servo 2 output select (3‑coil TMR) | Servo 2 output select (2‑coil simplex) |
JP17 | Servo 3 output select (3‑coil TMR) | Servo 3 output select (2‑coil simplex) |
JP18 | Servo 4 output select (3‑coil TMR) | Servo 4 output select (2‑coil simplex) |
JP19 | Servo 5 output select (3‑coil TMR) | Servo 5 output select (2‑coil simplex) |
JP20 | Servo 6 output select (3‑coil TMR) | Servo 6 output select (2‑coil simplex) |
The first two servo outputs (Servo 1 and Servo 2) also provide an external suicide function via terminals 107 and 108 (SVRL1, SVRL2). When an external contact closes across these terminals, the servo driver is disconnected from the output terminals and a passive circuit biases the servo closed. This feature is used when it is required to include servo action in a control protective response. If protective action is not needed, leave terminals 107 and 108 open.
5.3 LVDT Position Servo System
The IS400TCASH1AGD receives secondary‑side signals from LVDT sensors via the TCAT terminal board. These signals are conditioned by the BCAA acquisition board, converting the RMS voltage to a dc equivalent signal read by the processor through A/D converters. The PCAA firmware can run up to six independent digital servo regulators, each loop performed at a 100 Hz sample rate. The digital regulator output is written to a D/A converter, and the output of the D/A is the current command for the analog current regulator.
LVDT calibration is performed using ToolboxST software. The user selects LVDT calibration mode and sets the controller output CalibEnab# to TRUE. In calibration mode, the user can use the servo output in open‑loop mode to force the valve to the fully closed and fully open positions. During calibration, the PCAA assigns the RMS voltage representing the open and closed positions to the configuration parameters MinVrms and MaxVrms. The user then selects Calibrate and Save to store the LVDT excitation output voltage in the configurable parameter ExcitMonCal.
5.4 Thermocouple Configuration
The PCAA (including the IS400TCASH1AGD) supports the thermocouple types and temperature ranges listed in the specifications table. A single cold junction is provided with each PCAA module. The module accepts a controller backup cold junction value (CIBackup) in the event a problem is detected with the local sensor. The PCAA may be configured to use a controller‑provided remote cold junction value (CJRemote). All thermocouple inputs are biased with a dc voltage that drives the temperature signal full scale negative if an open wire occurs.
5.5 Important Configuration Note – ThermCplUnit Parameter
The ThermCplUnit parameter affects the native units of the controller application variable. It is only indirectly related to the tray icon and associated unit switching capability of the HMI. Do not change the ThermCplUnit parameter in ToolboxST because these changes will require corresponding changes to application code and to the Format Specification or units of the connected variable. This parameter modifies the actual value sent to the controller as seen by application code. Application code written to expect degrees Fahrenheit will not work correctly if this setting is changed. External devices such as HMIs and Historians may also be affected.
VI. Diagnostics and Alarms
The IS400TCASH1AGD, as part of the PCAA module, performs extensive self‑diagnostic tests. These include:
Power‑up self‑test (RAM, flash memory, Ethernet ports, and most processor board hardware)
Continuous monitoring of internal power supplies
Electronic ID check from terminal board, acquisition board, and processor board to confirm hardware match, followed by a check that application code loaded from flash is correct for the hardware
Group‑based high/low range checks for 4‑20 mA analog inputs; if a signal falls outside the specified range, signal health is declared bad
Precision reference voltages in each scan; measured values compared against expected values to confirm A/D converter health
Analog output current sensed on the terminal board using a small burden resistor; the pack conditions this signal and compares it to commanded current to confirm D/A converter health
Analog output suicide relay continuously monitored for agreement between commanded state and feedback indication
Thermocouple circuits biased with a small dc current; if a thermocouple opens, the temperature signal goes to a full‑scale negative reading
Seismic input circuits biased with a small dc current; if a seismic sensor circuit opens, an alarm is generated and signal health is set to indicate a problem
The following are typical alarms specific to the PCAA I/O pack that are relevant to the IS400TCASH1AGD:
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 thermocouple for open circuit; measure incoming millivolt signal; verify TC type matches configuration |
68 | Cold Junction Unhealthy, Using Backup | Local cold junction signal from TCAS terminal board is out of range (-50 to 85°C) | If hardware is in normal temperature range, possible cold junction sensor failure; replace PCAA module |
69‑80 | Analog Input (TCAS) [] Unhealthy | Excitation to transducer wrong or missing; faulty transducer; jumper settings mismatch configuration; input beyond specified range; open or short circuit | Check field wiring and connections; check field device; check PCAA ground select jumper; verify inputs in operable range (3.0‑21.5 mA, ±5.25 V, ±10.5 V) |
81‑104 | Analog Input (TCAT) [] Unhealthy | Same as above, plus TCAT‑PCAA cables not fully seated | Check field wiring; check TCAT‑PCAA cables are fully seated in connectors; verify inputs in operable range (3.0‑21.5 mA) |
117‑122 | LVDT Excitation [] Failed | Excitation ground fault; field wiring issue or LVDT sensor failure; internal hardware failure | Check field wiring including shields for LVDT excitation output; check LVDT sensor; if hardware failure, replace PCAA |
123‑134 | LVDT [] Excitation voltage out of range | Actual LVDT excitation goes out of range (±10% of ExcitMonCal); possible terminal board failure | Measure excitation voltage and verify against configuration parameter; check LVDT sensor; recalibrate servo; replace PCAA |
135‑146 | LVDT [] Position Out of Limit | Excitation issue; faulty transducer; open or short circuit; input out of range; LVDT not calibrated | Check field wiring and LVDT excitation; check LVDT sensor; calibrate servo regulator; verify MinVrms and MaxVrms limits; verify ExcitSelect matches excitation source; verify PositionMargin setting |
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 | Check and correct configuration parameters; verify regulator inputs are connected to ENABLED sensor inputs; use ToolboxST Advanced Diagnostics to view configuration errors |
161‑166 | Servo [] Output Suicide Active | Servo position/flow/pressure input issues; regulator feedback out of range; servo current feedback differs from command | Check configuration; verify inputs connected to used sensor inputs; check position sensor connections and mechanical integrity; check wiring of servo output loop for open or short circuit; check for short or open servo coil |
217 | TCAT Configuration and Hardware Mismatch | TCAT configured in ToolboxST but not connected; TCAT not configured but connected | Verify TCAT selection in ToolboxST matches actual hardware; verify P1 and P2 cable connections are not swapped; verify cables are screwed down and terminal boards properly grounded; perform power‑down reset to clear |
218 | TCAT Connector P1 and P2 Types Mismatch | Type (R/R, S/S, T/T) of P1 and P2 connections between TCAT and TCAS do not match | Check ToolboxST configuration and TCAT terminal board P1 and P2 cable connections; ensure no type mismatch |
VII. Installation Instructions
To install the PCAA module containing the IS400TCASH1AGD terminal board:
Securely mount the PCAA module in the designated panel or rack location.
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. Connectors on TCAT are paired by network connection: PR1/PR2 go to a PCAA connected to the R controller network, PS1/PS2 go to a PCAA connected to the S controller, and PT1/PT2 go to a PCAA connected to the T controller. Fully seat the cable mounting screws, finger‑tight only, 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. However, the PCAA is not sensitive to Ethernet connections and negotiates proper operation over either port. For TMR PCAA modules, the network connection should match the connection made to TCAT (e.g., the PCAA with R IONet connection should have cables going to TCAT PR1 and PR2 connectors).
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 a shield ground independent of the mounting sheet metal, 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. Refer to GEH‑6700 (ToolboxST User Guide for Mark VIe Control) for more information.
VIII. Ordering and Compatibility
The IS400TCASH1AGD is a field‑replaceable terminal board that is part of the PCAA Core Analog I/O Pack. When ordering, ensure compatibility with the following:
Processor board versions: PCAAH1A (BPPB) or PCAAH1B (BPPC with ControlST V04.04+)
Redundancy configuration: Simplex or TMR
Associated terminal boards: TCAT (optional for simplex, required for TMR), JGPA for shield termination and 24 V field power
Always verify that the electronic ID information from the terminal board, acquisition board, and processor board matches. If a mismatch is detected, the module will generate a diagnostic and may not operate correctly.
