The IS400TCASH1ADC is an important component of the PCAA (Core Analog I/O Pack) within the GE Mark VIe control system, specifically belonging to the TCAS series terminal board. As the field signal interface of the PCAA module, this terminal board provides customer terminals and signal routing, efficiently and reliably transmitting various analog signals from field devices such as gas turbines and compressors – including thermocouples, 4-20 mA transmitters, LVDTs (Linear Variable Differential Transformers), servo drivers, and pulse rate sensors – to the BCAA and BCAB analog processing boards inside the PCAA.
The IS400TCASH1ADC can be applied in simplex and TMR (Triple Modular Redundant) systems, meeting industrial requirements for high availability and high safety. It receives 28 V dc control power through the P5 connector and supplies 28 V dc power to the JGPA terminal board through the P4 connector for field cable shield termination. At the same time, the IS400TCASH1ADC 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.
As part of the PCAA module – the least replaceable unit (LRU) – the IS400TCASH1ADC works together with the BCAA main board, the BCAB interface board, and the BPPx processor board. The module employs surface‑mount technology, offering good resistance to vibration, temperature, and electromagnetic interference, and operates in harsh industrial environments from -30°C to 65°C.
II. Hardware Structure and Interfaces
2.1 Physical Dimensions and Mounting
The physical dimensions of the IS400TCASH1ADC are consistent with standard TCAS modules:
Height: 8.26 cm (3.25 inches)
Width: 4.19 cm (1.65 inches)
Depth: 12.1 cm (4.78 inches)
The module uses Euro style pluggable box‑type terminal blocks for easy field wiring and maintenance. During installation, the PCAA module is securely mounted in a cabinet or on a panel; the IS400TCASH1ADC, as part of the PCAA, is fixed as a whole and does not need to be removed separately.
2.2 Main Connectors
Connector | Type | Description |
P5 | 3‑pin power connector | Inputs 28 V dc power for the entire PCAA module and terminal board. Note: power enters directly through this 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 / 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 interfaces | Primary and redundant IONet network interfaces for high‑speed data exchange with the controller. |
120 Euro terminals | Pluggable box‑type terminals | For field device signal wiring; support solid wires, stranded wires, and wires with ferrules. |
2.3 Terminal Wiring Specifications
The Euro terminals of the IS400TCASH1ADC support the following conductor types and cross‑sections:
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 |
III. Signal Types and I/O Allocation
The IS400TCASH1ADC handles the main signal access tasks on the PCAA terminal side. According to the signal assignment table (PCAA Terminals) in the attached document, signals wired directly to this terminal board include:
3.1 Signals Wired Directly to the IS400TCASH1ADC
Number of Signals | Signal Type | Screws per Signal |
25 | Thermocouple inputs (supports types E, J, K, S, T) | 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) | 2 |
6 | LVDT excitation outputs (7 Vrms, 3.2 kHz, 60 mA) | 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 (the IS400TCASH1ADC also participates)
Number of Signals | Signal Type | Screws per Signal |
12 | Fanned seismic inputs (velocity sensors) | 2 |
24 | Fanned analog 4‑20 mA inputs (from TCAT) | 2 |
12 | 24 V output power (25 mA each, for transmitters) | 2 |
3 | Voting 4‑20 mA outputs (for TMR applications) | 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
Signal Type | Specified Accuracy (including all errors) | Typical Accuracy (at 25°C) |
Thermocouple inputs | ±0.10% of full scale (-13.8 to +45.5 mV) | ±0.06% |
Analog 4‑20 mA inputs | ±0.25% | ±0.10% |
Analog 0‑10 V inputs | ±0.50% | ±0.20% |
Pulse/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 Vrms ±5.00% | ±3.00% |
Servo output (±10 mA) | ±3.50% | ±0.70% |
Analog 4‑20 mA output | ±0.75% | ±0.43% |
24 V power output | 24 V dc ±0.5% (0‑25 mA) | — |
V. Configuration and Operation
Each analog input channel on the IS400TCASH1ADC has a jumper (JP1 through JP12) to select whether the return terminal is grounded (GND) or floating (OPEN). The default position is 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 output terminals, each capable of powering one 4‑20 mA two‑wire transmitter.
5.2 Servo Output Configuration
The six servo outputs can each be configured via jumpers (JP15 through JP20) as:
The first two servo outputs (Servo 1 and Servo 2) additionally provide an external suicide function via terminals 107 and 108 (SVRL1, SVRL2). When an external contact closes across these terminals, the servo drive circuit is disconnected from the digital regulator and the valve is forced closed through a current limiting resistor (15 mA fixed output) for protective response.
5.3 LVDT Position Servo System
The IS400TCASH1ADC 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 voltage, and read by the processor through A/D converters. The PCAA firmware can run up to six independent digital servo regulators, each 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.
LVDT calibration is performed using ToolboxST software: the user drives the valve to the fully closed and fully open positions, and the software automatically records the corresponding Vrms values (MinVrms / MaxVrms). The calibrated values are used to convert real‑time Vrms into a 0%–100% position percentage.
5.4 Thermocouples and Cold Junction Compensation
Each PCAA module includes a built‑in cold junction temperature sensor for thermocouple reference junction compensation. If the local sensor fails, a backup value (CIBackup) or a controller‑provided remote cold junction value (CJRemote) can be configured. All thermocouple inputs have open‑wire detection bias circuitry: when a thermocouple opens, the signal is biased to negative full scale for easy diagnostics.
VI. Diagnostics and Alarms
As part of the PCAA module, the IS400TCASH1ADC provides comprehensive self‑diagnostic capabilities. The following are typical alarms closely related to this terminal board (based on the PCAA‑specific alarms in the attached document):
Alarm Code | Description | Possible Cause | Solution |
33‑67 | Thermocouple unhealthy | Millivolt input exceeds range; wrong type configured; open wire; stray voltage | Check field wiring and shielding; measure millivolt signal; verify TC type matches configuration |
68 | Cold junction unhealthy, using backup | Local TCAS cold junction signal out of range (-50 to 85°C) | Check temperature; if normal, possible cold junction sensor failure – replace PCAA module |
69‑80 | TCAS analog input unhealthy | Wrong or missing excitation to transmitter; faulty transmitter; jumper‑configuration mismatch; input out of range | Check field wiring and device; check ground jumper; verify input within 3.0‑21.5 mA, ±10.5 V |
81‑104 | TCAT analog input unhealthy | As above, plus TCAT‑PCAA cables not fully seated | Check that cables are tightened; verify P1/P2 connections are secure |
117‑122 | LVDT excitation failed | Excitation ground fault; field wiring or LVDT sensor failure; internal hardware failure | Check LVDT excitation wiring and shielding; check LVDT sensor; if hardware failure, replace PCAA |
123‑134 | LVDT excitation voltage out of range | Actual excitation voltage deviates by >±10% from ExcitMonCal | Measure excitation voltage; recalibrate servo; replace PCAA |
135‑146 | LVDT position out of limit | LVDT excitation issue; sensor failure; not calibrated; MinVrms/MaxVrms improperly set | Check LVDT wiring and sensor; recalibrate; verify ExcitSelect matches excitation source |
155‑160 | Servo disabled: configuration error | Regulator position/flow/pressure input connected to an unused channel | Check configuration parameters; ensure inputs are connected to enabled sensors |
161‑166 | Servo output suicide active | Feedback out of range; excessive error between commanded current and feedback | Check position sensor connections and mechanical integrity; check servo output loop for open or short |
217 | TCAT configuration and hardware mismatch | TCAT configured in ToolboxST but not connected; TCAT connected but not configured; cables swapped | Verify configuration matches hardware; check P1/P2 cables are not swapped; re‑tighten cables and ensure grounding; power‑cycle to clear |
218 | TCAT connector P1/P2 type mismatch | Connection types (R/R, S/S, T/T) do not match | Check P1/P2 cable connections between TCAT and TCAS to ensure type consistency |
VII. Installation and Operation Key Points
7.1 Installation Steps
Securely mount the PCAA module (which includes the IS400TCASH1ADC terminal board).
Connect the JGPA power connection to the P4 connector on the PCAA.
If using TCAT, connect the PCAA module to the TCAT terminal board using two 68‑pin cables on connectors P1 and P2 (matching PR1/PR2, PS1/PS2, or PT1/PT2 on TCAT). Finger‑tighten only the cable mounting screws to ensure proper cable grounding. Failure to tighten may prevent the PCAA from reading the TCAT electronic ID and degrade signal quality.
Plug in one or two Ethernet cables depending on the system configuration. When a single IONet connection is used, the module works 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 terminals. In most applications, they are grounded through the mounting sheet metal. If independent shield ground is required, 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 and the IS400TCASH1ADC parameters as necessary.
7.2 Important Notes
Power: The module must receive 28 V dc power directly from the P5 connector; do not power it through the processor board power connector.
68‑pin cable removal: When removing the cables, ensure that the hex posts in the board‑mounted connectors do not turn while backing out the thumbscrews, to avoid damaging the connectors.
Grounding: The P1/P2 cables must be properly grounded; otherwise, electronic ID reading and analog signal accuracy may be affected.
Configuration warning: Do not arbitrarily change the ThermCplUnit parameter in ToolboxST, as this changes the engineering units of thermocouple signals seen by the application code and may affect application logic and HMI displays.
