The IS200DTTCH1A is a Simplex Thermocouple Input Terminal Board designed by General Electric (GE) for its Mark VI Control System. This board is the standard version within the DTTC series, featuring a compact design specifically for DIN-rail mounting. It provides the control system with 12 thermocouple input channels for signal acquisition and processing. The IS200DTTCH1A board works in conjunction with the VTCC thermocouple processor board, connecting via a single 37-pin cable to acquire 12 thermocouple signals.
The design of the IS200DTTCH1A boards industrial field space limitations and application requirements. Its compact dimensions allow multiple boards to be stacked vertically on a DIN rail, significantly saving control cabinet space. The board features a permanently mounted high-density Euro-Block type terminal block with 42 terminals for connecting thermocouple wires. An onboard ID chip identifies the board to the VTCC for system diagnostic purposes.
Key features of the IS200DTTCH1A include:
Compact Design: Suitable for DIN-rail mounting, can be stacked vertically to save cabinet space.
12 Thermocouple Inputs: Supports temperature measurement with various thermocouple types.
Coordination with VTCC: Connects to the VTCC processor board via a single 37-pin cable. Each VTCC can support two DTTC boards, providing 24 thermocouple inputs total.
Onboard Signal Conditioning: Features the same signal conditioning circuits and Cold Junction (CJ) reference as the TBTC board.
Cold Junction Compensation: Reference junction temperature measured at one location, with CJ accuracy of 1.1°C (2°F).
Open Circuit Detection: Injects a very small current into each thermocouple path to detect open circuit faults.
Hardware Limit Checking: Preset (non-configurable) high/low hardware limit checks; exceeding limits stops scanning the channel and generates an alarm.
ID Chip Identification: Onboard ID chip read by the VTCC ensures hardware compatibility.
Shield Connections: A shield connection point is provided for every third terminal, internally connected to SCOM.
Jumperless Design: The board has no configurable jumpers; all functions are fixed, simplifying field maintenance.
The board operates within a temperature range of 0 to 60°C, suitable for industrial control cabinet environments. It is important to note that the DTTC is only available in a simplex version, does not support TMR applications, and is not compatible with the PTCC I/O pack.
II. Main Functions
The primary functions of the IS200DTTCH1A include, but are not limited to, the following:
1. Thermocouple Signal Acquisition
The IS200DTTCH1A board provides 12 thermocouple input channels for acquiring signals from various field temperature sensors. Thermocouple types can be configured via the VTCC processor board, supporting common types (such as J, K, T, E, etc.).
2. Cold Junction Compensation
The board features a Cold Junction (CJ) reference circuit, measuring the reference junction temperature at a single location. VTCC provides excitation for the CJ reference on the DTTC. The cold junction temperature measurement accuracy is 1.1°C (2°F), ensuring the accuracy of thermocouple measurements.
3. Signal Conditioning
The IS200DTTCH1A features the same onboard signal conditioning circuits as the TBTC board, including:
The conditioned signals are transmitted via the connector to the VTCC processor board for analog-to-digital conversion.
4. Open Circuit Detection
When operating with the I/O processor, VTCC injects a very small current into each thermocouple path. The polarity of this current causes a high-temperature reading if a thermocouple opens, allowing open circuit faults to be detected. This is an effective online diagnostic method for timely identification of sensor faults.
5. Hardware Limit Checking
Each thermocouple type has preset (non-configurable) high/low hardware limit checks, set near the ends of the operating range. If VTCC detects an input signal exceeding these limits, it sets a logic signal and stops scanning that input channel. Any input channel triggering a hardware limit generates a composite diagnostic alarm, L3DIAG_VTCC, indicating a problem with the entire board.
6. ID Chip Identification
The board features a read-only ID chip storing the board's serial number, type, and revision number. VTCC reads this information during initialization. If a mismatch is encountered, a hardware incompatibility fault is generated, preventing system problems caused by incorrect configuration.
7. Shield Connections
A shield connection point is provided for every third terminal on the board. These shield points are internally connected to SCOM. This design provides convenient shield grounding for thermocouple wires, reducing the impact of electromagnetic interference on measurement signals.
III. System Applications
1. Application in Mark VI Control System
The IS200DTTCH1A is a compact terminal board for temperature measurement within the Mark VI control system. Its roles within the system include:
Process Temperature Monitoring: Acquires critical temperature points for equipment such as gas turbines and steam turbines, including exhaust temperature, bearing temperature, and cooling medium temperature.
Exhaust Overtemperature Protection: In gas turbine applications, provides input signals for overtemperature protection by monitoring exhaust temperature.
Performance Monitoring: Acquires various temperature parameters for efficiency and performance calculations.
Remote I/O Expansion: Flexibly expands the system's temperature measurement capacity by stacking multiple DTTC boards.
2. Differences from TBTC
The main differences between DTTC and TBTC are size and mounting method:
| Feature | DTTC | TBTC |
| Size | Compact | Standard size |
| Mounting Method | DIN-rail | Panel mount |
| Number of Channels | 12 | 12 |
| Signal Conditioning | Same | Same |
| Cold Junction Compensation | Same | Same |
| Stackability | Can be stacked vertically | Not stackable |
| Connection Cable | Same 37-pin cable | Same 37-pin cable |
3. Typical Application Scenarios
Gas Turbine Control: Monitoring exhaust temperature, compressor discharge temperature, combustion chamber temperature, etc.
Steam Turbine Control: Monitoring main steam temperature, reheat steam temperature, extraction steam temperature, etc.
Generator Monitoring: Monitoring stator winding temperature, bearing temperature, cooling medium temperature, etc.
Heat Recovery Steam Generators (HRSG): Monitoring flue gas temperature and steam temperature in various sections.
Industrial Furnace Control: Monitoring furnace temperature, flue temperature, etc.
IV. Detailed Interface Description
1. Terminal Block
The IS200DTTCH1A features a permanently mounted 42-terminal Euro-Block type terminal block for connecting thermocouple wires. Terminal assignments are as follows:
Terminals 1-40: 12 thermocouple inputs (each input uses multiple terminals; refer to the wiring diagram for specific allocation).
Terminals 41-42: SCOM (shield common), must be connected to ground with the shortest possible wire.
Shield Connection Points: Provided for every third terminal (e.g., terminals 3, 6, 9, etc.), internally connected to SCOM, for connecting the shields of thermocouple wires.
2. Connector
The board connects to the VTCC thermocouple processor board via a single 37-pin cable connector (JA1). This cable transmits the 12 thermocouple signals, cold junction compensation signal, and ID chip information to the VTCC processor board for processing.
3. Grounding Requirements
Important: SCOM (terminals 41 and 42) must be connected to ground with the shortest possible wire to ensure shielding effectiveness and measurement stability. The shield connection points on the board are internally connected to SCOM, so grounding the SCOM terminal is sufficient.
4. Cold Junction Compensation
VTCC provides excitation for the cold junction compensation reference on the DTTC. The cold junction compensation sensor is located on the board and measures the reference junction temperature. During installation, ensure the cold junction compensation area is not affected by external heat sources for accurate compensation.
V. Diagnostics and Maintenance
1. Diagnostic Functions
The IS200DTTCH1A provides the following diagnostic functions via the VTCC:
| Diagnostic Item | Description |
| Hardware Limit Checking | Each thermocouple type has preset hardware high/low limits. Exceeding limits stops scanning the channel and sets a logic signal. Any channel exceeding limits generates the L3DIAG_VTCC composite diagnostic alarm. |
| Open Circuit Detection | VTCC injects a very small current into each thermocouple path to detect open circuit faults. An open circuit results in a high-temperature reading for easy identification. |
| ID Chip Verification | VTCC reads the onboard ID chip and compares it with the configuration. A mismatch generates a hardware incompatibility fault. |
2. Viewing Diagnostic Details
Details of individual diagnostics can be viewed via the Toolbox software. Diagnostic signals can be individually latched and reset with the RESET_DIA signal after returning to normal.
3. Common Troubleshooting
| Fault Symptom | Possible Cause | Troubleshooting Suggestions |
| No reading on a channel | Thermocouple open circuit, wiring error, channel fault | Check thermocouple and wiring, test thermocouple continuity with a multimeter |
| Reading abnormally high/low | Incorrect thermocouple type configuration, cold junction compensation issue | Check thermocouple type configuration, check the cold junction compensation area |
| Reading fluctuating or unstable | Poor shield grounding, electromagnetic interference | Check SCOM grounding, check shield connections |
| L3DIAG_VTCC composite diagnostic alarm | A channel has exceeded limits | Identify the specific fault channel, check the corresponding thermocouple and measurement point |
| Hardware incompatibility fault | ID chip information mismatch | Verify correct board model, contact GE technical support |
4. Maintenance Recommendations
Periodic Inspection: Check terminal blocks for looseness and wires for oxidation.
Cleaning: Regularly clean the board to prevent dust accumulation affecting heat dissipation and insulation.
ESD Protection: Wear a grounding strap when handling the board and store it in anti-static bags.
Spare Parts Management: Maintain a spare IS200DTTCH1A board to reduce downtime in case of failure.
VI. Installation and Configuration
1. Installation Steps
Mount DIN Rail Holder: Install the plastic holder onto the DIN rail.
Install Board: Slide the DTTC board into the holder until it snaps into place.
Connect Thermocouple Wires: Connect thermocouple wires to the terminal block. Use #18 AWG wire.
Connect Shields: Connect the shields of the thermocouple wires to the corresponding shield connection points.
Ground Connection: Connect terminals 41 and 42 (SCOM) to ground using the shortest possible wire.
Connect Cable: Connect the 37-pin cable to the board's JA1 connector and to the VTCC processor board.
Verify Installation: Confirm all connections are secure.
2. Multi-Board Stacking
When multiple DTTC boards are required, they can be stacked vertically on the DIN rail. Each board connects independently to the VTCC processor board (each VTCC can support up to two DTTC boards). When stacking, ensure adequate spacing between boards for heat dissipation and wiring access.
3. Wiring Precautions
Use appropriately sized thermocouple extension wire or compensating cable.
Thermocouple wires should be shielded, with the shield grounded at the DTTC end.
The SCOM connection should be as short as possible and connected directly to ground.
Avoid running thermocouple wires parallel to power cables to reduce electromagnetic interference.
Ensure the cold junction compensation area is not affected by external heat sources.
4. Configuration Method
The IS200DTTCH1A board has no configurable jumpers. All configuration (such as thermocouple type, range, etc.) is done via the VTCC processor board's software. Users must configure the corresponding parameters in the Toolbox software.
