The IS200DRTDH1A is a Simplex RTD Input Terminal Board designed by General Electric (GE) for its Mark VI Control System. This board is the standard version within the DRTD series, featuring a compact design specifically for DIN-rail mounting. It provides the control system with 8 RTD (Resistance Temperature Detector) input channels for signal acquisition and processing. The IS200DRTDH1A board works in conjunction with the VRTD processor board, connecting via a single 37-pin cable to acquire 8 RTD signals.
The design of the IS200DRTDH1A 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. Each VRTD processor board can support two DRTD boards, providing a total of 16 temperature inputs. The board features a permanently mounted Euro-Block type terminal block with 36 terminals for connecting RTD wires. An onboard ID chip identifies the board to the VRTD for system diagnostic purposes.
Key features of the IS200DRTDH1A include:
Compact Design: Suitable for DIN-rail mounting, can be stacked vertically to save cabinet space.
8 RTD Inputs: Supports three-wire RTDs, capable of measuring various RTD types.
Coordination with VRTD: Connects to the VRTD processor board via a single 37-pin cable. Each VRTD can support two DRTD boards, providing 16 RTD inputs total.
Long-Distance Measurement: RTDs can be located up to 300 meters (984 feet) from the control cabinet, with a maximum two-way cable resistance of 15 Ω.
Excitation Current: Provides 10 mA dc multiplexed (non-continuous) excitation current, supporting grounded or ungrounded RTDs.
Noise Suppression: Features similar noise suppression as the TRTD board.
Fault Detection: Can detect RTD open circuits, short circuits, and out-of-hardware-limit conditions.
Multiple RTD Types: Supports 15 RTD types, covering a wide temperature range.
ID Chip Identification: Onboard ID chip read by the VRTD ensures hardware compatibility.
Jumperless Design: The board has no configurable jumpers; all functions are fixed, simplifying field maintenance.
The board operates within a temperature range of -30 to 65°C, suitable for industrial control cabinet environments. It is important to note that the DRTD is only available in a simplex version, does not support TMR applications, and is not compatible with the PRTD I/O pack.
II. Main Functions
The primary functions of the IS200DRTDH1A include, but are not limited to, the following:
1. RTD Signal Acquisition
The IS200DRTDH1A board provides 8 three-wire RTD input channels for acquiring signals from various field temperature sensors. Each RTD connects to the terminal block on the board via three wires: excitation positive, signal positive, and common (B wire).
2. Excitation Current Supply
The board, via the VRTD processor board, supplies a 10 mA dc multiplexed (non-continuous) excitation current to each RTD. This design reduces power consumption and self-heating effects, improving measurement accuracy. RTDs can be either grounded or ungrounded, adapting to different field installation conditions.
3. Long-Distance Measurement Support
RTDs can be installed at locations remote from the control cabinet, up to a maximum distance of 300 meters (984 feet), with a maximum two-way cable resistance of 15 Ω. This feature allows RTDs to be flexibly deployed at various measurement points in the industrial field without requiring the control cabinet to be located near the equipment under test.
4. Signal Conditioning and Noise Suppression
The IS200DRTDH1A features similar onboard noise suppression as the TRTD board, including filtering and surge protection, ensuring signal integrity in harsh industrial environments. All RTD signals undergo noise suppression processing upon entering the board, effectively reducing the impact of electromagnetic interference.
5. Analog-to-Digital Conversion and Scanning
The VRTD's VCO type A/D converter uses voltage to frequency converters and sampling counters. The converter samples each signal and the excitation current at a time interval related to the power system frequency:
6. Linearization Processing
The digital signal processor within the VRTD performs linearization of the RTD signals via software, supporting 15 RTD types, including platinum, copper, nickel, and other materials, covering a wide temperature range.
7. Fault Detection
RTD open and short circuits are detected by out-of-range values. When an RTD is determined to be outside the hardware limits, that input channel is removed from the scanned inputs to prevent adverse effects on other input channels. Repaired channels can be reinstated automatically after 20 seconds or can be manually reinstated.
8. ID Chip Identification
The board features a read-only ID chip storing the board's serial number, type, revision number, and connector location information. The VRTD reads this information during initialization. If a mismatch is encountered, a hardware incompatibility fault is generated, preventing system problems caused by incorrect configuration.
III. System Applications
1. Application in Mark VI Control System
The IS200DRTDH1A is a compact terminal board for temperature measurement within the Mark VI control system, widely used for temperature monitoring in gas turbines, steam turbines, generators, and other equipment. Working with the VRTD processor board, it forms a complete RTD input subsystem.
In the system, IS200DRTDH1A plays the following roles:
Temperature Monitoring: Acquires critical temperature points such as bearing temperature, exhaust temperature, and cooling medium temperature.
Process Control: Provides feedback signals for temperature control loops.
Protection Functions: Provides input signals for overtemperature protection.
Performance Monitoring: Acquires temperature parameters for efficiency and performance calculations.
2. Differences from TRTD
The main differences between DRTD and TRTD are size and mounting method:
| Feature | DRTD | TRTD |
| Size | Compact | Standard size |
| Mounting Method | DIN-rail | Panel mount |
| Number of Channels | 8 | 16 |
| Stackability | Can be stacked vertically | Not stackable |
| Connection Cable | Same 37-pin cable | Same 37-pin cable |
| Compatibility | Not compatible with PRTD | Compatible with PRTD |
3. Typical Application Scenarios
Gas Turbines: Monitoring compressor inlet/outlet temperatures, bearing temperatures, etc.
Steam Turbines: Monitoring bearing temperatures, cylinder temperatures, etc.
Generators: Monitoring stator winding temperature, bearing temperature, cooling medium temperature, etc.
Auxiliary Equipment: Monitoring oil system temperature, cooling water system temperature, etc.
Small Control Systems: Suitable for small control systems with limited I/O points and space.
IV. Detailed Interface Description
1. Terminal Block
The IS200DRTDH1A features a permanently mounted 36-terminal Euro-Block type terminal block for connecting the 8 three-wire RTDs. Terminal assignments are as follows:
Terminals 1-24: 8 RTD inputs (each input uses 3 terminals: excitation, signal, common).
Terminals 25-34: Spare terminals.
Terminals 35-36: SCOM (shield common), must be connected to ground.
2. Connector
The board connects to the VRTD processor board via a single 37-pin D-type connector with latching fasteners. This cable is identical to those used on the TRTD terminal board, facilitating spare parts management.
3. Grounding Requirements
Important: SCOM (terminals 35 and 36) must be connected to ground to ensure shielding effectiveness and system stability. The board has no dedicated shield terminal strip, making this ground connection particularly critical. The ground wire should be as short as possible.
4. Wiring Precautions
Use #18 AWG shielded twisted triplet wire.
Optional Ground: The B wire can be connected to ground.
RTD Group Wiring: B wires can be shared; tie the B wires together at the RTDs, tie the signal wires together at the terminal board, and interconnect with one wire.
V. Diagnostics and Maintenance
1. Diagnostic Functions
The IS200DRTDH1A provides the following diagnostic functions via the VRTD:
| Diagnostic Item | Description |
| Hardware Limit Check | Each RTD 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_VRTD composite diagnostic alarm. |
| System Limit Check | Each RTD input has system limit checking based on configurable high/low levels, which can be used to generate alarms and configured as latching or non-latching. |
| ID Chip Verification | The VRTD reads the board's ID chip and compares it with the configuration. A mismatch generates a hardware incompatibility fault. |
| RTD Resistance Check | Checks the resistance of each RTD and compares it with the correct value. If high or low, a fault is created. |
2. Fault Handling
When a channel exceeds hardware limits, it is removed from the scanned inputs to prevent affecting other channels.
Repaired channels can be automatically reinstated after 20 seconds or manually reinstated.
Diagnostic signals can be individually latched and reset with the RESET_DIA signal after returning to normal.
System limit out-of-range signals can be reset with RESET_SYS.
3. Common Troubleshooting
| Fault Symptom | Possible Cause | Troubleshooting Suggestions |
| No reading on a channel | RTD open circuit, wiring error, channel fault | Check RTD and wiring, measure RTD resistance |
| Reading abnormally high/low | Incorrect RTD type configuration, excessive lead resistance | Check RTD type configuration, check cable resistance |
| Reading fluctuating or unstable | Poor shield grounding, electromagnetic interference | Check SCOM grounding, check cable routing |
| L3DIAG_VRTD composite diagnostic alarm | A channel has exceeded limits | Identify the specific fault channel, check the corresponding RTD 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 IS200DRTDH1A 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 DRTD board into the holder until it snaps into place.
Connect RTD Wires: Connect the three wires of each RTD to the corresponding terminals on the terminal block. Use #18 AWG shielded twisted triplet wire.
Ground Connection: Connect terminals 35 and 36 (SCOM) to ground using the shortest possible wire.
Connect Cable: Connect the 37-pin cable to the board and to the VRTD processor board.
Verify Installation: Confirm all connections are secure.
2. Multi-Board Stacking
When multiple DRTD boards are required, they can be stacked vertically on the DIN rail. Each board connects independently to the VRTD processor board (each VRTD can support up to two DRTD boards). When stacking, ensure adequate spacing between boards for heat dissipation and wiring access.
3. Wiring Precautions
Use shielded twisted triplet wire to reduce electromagnetic interference.
The SCOM connection should be as short as possible and connected directly to ground.
For optional grounding, the B wire can be connected to ground as needed.
When grouping wiring, ensure reliable connections for the B wires of each RTD.
