The IS200STTCH2A is a compact, high-density simplex thermocouple input terminal board within the General Electric (GE) Mark VIe control system. As an important member of the STTC family, the IS200STTCH2A is specifically designed to connect to the PTCC thermocouple processor board (model IS220PTCC), providing 12 thermocouple temperature signal acquisition channels for industrial process control. The board integrates high-precision signal conditioning circuitry and a cold junction temperature reference, enabling it to accurately convert weak millivolt signals from various types of field thermocouples into digital temperature values. It is widely used in high-temperature measurement applications in power generation, petrochemical, steel, and glass industries.
A distinguishing feature of the IS200STTCH2A is its pluggable Euro-block terminal block design, which makes on-site wiring and future maintenance extremely convenient. Its signal conditioning and cold junction compensation circuitry are identical to those on the larger TBTC terminal board, achieving the same level of accuracy and reliability in a compact form factor. The board includes an onboard ID chip that supports system-level hardware identification and automatic fault diagnostics. Working with the PTCC I/O pack, it seamlessly connects to the Mark VIe control network via Ethernet, establishing an integrated temperature acquisition chain from the thermocouple to the controller.
System Positioning and Compatibility
Within the Mark VIe control architecture, the IS200STTCH2A serves as the front-end temperature acquisition unit for distributed I/O, positioned between the controller's Ethernet network and the field thermocouple sensors. The PTCC I/O pack plugs directly into the DC-37 pin connector (JA1) on the IS200STTCH2A board and communicates with the controller via dual RJ-45 Ethernet ports. One IS200STTCH2A corresponds to one PTCC I/O pack, forming a compact simplex temperature acquisition unit.
It is important to note that the IS200STTCH2A is specifically intended for the Mark VIe control system and is only compatible with the PTCC I/O pack (all versions of IS220PTCC). It is not compatible with the YTCC I/O pack used in the Mark VIeS safety system. The board supports only simplex operation and does not support Triple Modular Redundant (TMR) applications. If thermocouple inputs with a SIL safety rating are required, the STTCS2A model (pluggable terminals, IEC 61508 safety certified, used in conjunction with YTCC) should be selected.
Core Functional Features
1. 12 Thermocouple Input Channels
The IS200STTCH2A provides 12 thermocouple input channels. When used with different versions of the PTCC I/O pack, it supports a wide range of standard thermocouple types. With the PTCCCH1 version, it supports types E, J, K, S, T and millivolt inputs. With the PTCCCH2 version, support for types B, N, and R is added. This compatibility covers nearly all commonly used thermocouple types in industrial temperature measurement, allowing flexible adaptation to various process temperature measurement requirements.
2. Wide-Range Millivolt Signal Acquisition
The IS200STTCH2A board integrates precision signal conditioning circuitry. When used with PTCCCH1, the input signal range is -8 mV to +45 mV. When used with PTCCCH2, the input signal range is -20 mV to +95 mV. These ranges cover the thermoelectric potential generated by each thermocouple type across its operating temperature range and provide sufficient upper margin. After on-board filtering and anti-interference processing, the signals are sent to the A/D converter in the PTCC I/O pack for digitization through the DC-37 connector.
3. Cold Junction Temperature Compensation
The working principle of thermocouples necessitates compensation for the temperature of the cold (reference) junction. The IS200STTCH2A board integrates a cold junction temperature reference measurement circuit, for which the PTCC I/O pack provides the excitation source. The cold junction temperature is measured at a single fixed location on the board and serves as the compensation reference for all 12 channels. Cold junction temperature measurement accuracy over the Celsius operating range is 1.1°C, and over the Fahrenheit operating range is 2°F. This level of accuracy ensures the overall thermocouple measurement precision under typical ambient temperature conditions found in industrial control cabinets.
4. Pluggable Terminal Design
The IS200STTCH2A employs a right-angle header that accepts a variety of commercially available standard pluggable Euro-block terminal blocks, totaling 42 terminals. The pluggable design offers significant convenience compared to fixed-terminal versions: during field wiring, all thermocouple extension wires can be pre-wired to the pluggable terminal block, which can then be inserted as a single unit onto the board for quick installation. When replacing the board, only the terminal block needs to be unplugged, the board swapped, and the block plugged back in—no individual wire disconnection or reconnection is required. This drastically reduces downtime caused by board failures.
5. Onboard Diagnostics and Identification
A read-only ID chip is integrated onto the IS200STTCH2A board, storing the terminal board's serial number, board type, revision number, and connector location information. The PTCC I/O pack reads this ID chip data during power-up initialization. If a mismatch is detected between the actual connected board model and the configured one, a hardware incompatibility fault alarm is immediately generated, effectively preventing system abnormalities caused by incorrect board insertion.
During operation, the PTCC I/O pack injects a very small detection current into each thermocouple channel path. This is used to detect open circuits in the thermocouple or its wiring. If an open circuit occurs, due to the designed polarity of the injection current, the temperature reading for that channel will drift in the low-temperature direction, allowing the control system to trigger an open-circuit alarm. Furthermore, each thermocouple type has preset hardware high/low limits. When an input signal exceeds its operating range, the corresponding channel is automatically removed from the scan sequence and a composite diagnostic alarm is generated, preventing a faulty channel from adversely affecting other normal channels.
6. Zero Configuration, Plug-and-Play
The IS200STTCH2A is designed as a zero-hardware-configuration board: there are no jumpers, switches, or adjustable components on the board. All channel configuration, thermocouple type selection, range settings, alarm limits, and other parameters are performed by the PTCC I/O pack through the ToolboxST application software. This design eliminates the need for field engineers to perform specific settings and tests on each terminal board, significantly reducing installation and commissioning time, while also minimizing the risk of system failures caused by human configuration errors.
Installation and Wiring Highlights
The installation steps for the IS200STTCH2A are straightforward: first, assemble the plastic insulator and the terminal board onto a metal carrier, then snap the carrier onto a standard 35 mm DIN rail. If direct panel mounting is required, the carrier and insulator assembly can be bolted directly. Sufficient space should be left around the board for heat dissipation and wiring.
When wiring, thermocouple extension wires must be connected directly to the terminal block. The use of #18 AWG (approximately 0.8 mm²) wires is recommended. The shield of any shielded cable should be terminated on the designated shield terminals on terminal block TB1 (internally connected to SCOM) to ensure noise immunity. Using the pluggable terminal blocks: insert the stripped extension wire ends into the corresponding holes of the terminal block and tighten the screws. After confirming the connections are secure, align the entire terminal block with the right-angle header on the board and push it into place to complete the electrical connection. Pay attention to the polarity of the thermocouple extension wires to ensure correct positive and negative connections.
The board has two holes (E1 and E2) for chassis grounding screws, through which the board can be grounded to the cabinet's Protective Earth (PE) system. Proper grounding is critical for ensuring measurement accuracy and noise immunity.
Diagnostics and Maintenance
The IS200STTCH2A, working with the PTCC I/O pack, provides diagnostic coverage spanning board identification, channel health status, and sensor integrity. When a hardware over-limit or open-circuit fault occurs, the relevant diagnostic alarm signals are presented in the controller, and detailed channel-level diagnostic information is available through the ToolboxST application.
During maintenance, if the IS200STTCH2A board needs to be replaced, simply disconnect the I/O pack from the terminal board, unplug the terminal block, replace the board, plug the terminal block back in, and reconnect the I/O pack. The entire process requires no rewiring and no reconfiguration of the PTCC I/O pack (provided the replacement board is the identical model, and this board has no jumpers). This greatly reduces maintenance labor hours and dependency on personnel skills.
Application Scenarios
The IS200STTCH2A is suitable for various industrial applications requiring high-temperature measurement and process temperature monitoring. Typical applications include:
Monitoring of gas turbine and steam turbine exhaust temperatures.
Measurement of combustion chamber and boiler furnace temperatures.
Temperature control for heat treatment furnaces and glass melting tanks.
Temperature monitoring in flue gas desulfurization and denitrification processes.
Temperature monitoring of high-temperature media in chemical reactors and pipelines.
Bearing and lubricant temperature monitoring for auxiliary equipment in power plants.
For Mark VIe systems requiring up to 12 thermocouple inputs with a simplex architecture, the IS200STTCH2A, paired with a PTCC I/O pack, provides a compact, reliable, and precise temperature acquisition solution.
