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The Schneider Electric TM2ARI8LT is an 8-channel temperature input expansion module for the Modicon M238 logic controller. It is used to acquire temperature measurements from PT100 and PT1000 resistance temperature detectors (RTDs), allowing the PLC to monitor multiple temperature points within a machine or industrial process.
Unlike general-purpose analog input modules that accept standard voltage or current signals, the TM2ARI8LT is specifically configured for resistance temperature measurement. It supports PT100 probes over a range of -200 to 600°C and PT1000 probes over a range of -50 to 200°C.
This configuration is useful in applications where several temperature measurement points must be monitored by one controller. For example, an industrial heating system may require separate measurements from heating chambers, process pipes, fluid tanks, and equipment surfaces. The TM2ARI8LT collects these sensor signals and transfers the measured values to the PLC for processing.
The module uses 12-bit conversion resolution and provides eight independent temperature input channels. Its self-scanning acquisition arrangement allows the controller to receive measurements from multiple connected probes without requiring a separate temperature transmitter for every measurement point.
The TM2ARI8LT also supports broken-wire detection and out-of-range detection. These functions help identify sensor connection problems and abnormal measurement conditions during machine operation.
Electrical isolation between the input circuitry and internal logic is provided through photocoupler-based isolation. The module uses an external 24 V DC supply and two removable screw terminal blocks, one for sensor connections and another for power supply wiring.
For existing Modicon M238 installations, the TM2ARI8LT is particularly useful when additional RTD temperature measurement channels are required without changing the main PLC configuration.
| Parameter | Specification |
|---|---|
| Manufacturer | Schneider Electric |
| Model | TM2ARI8LT |
| Product Series | Modicon M238 |
| Product Type | Analog Input Module |
| Number of Analog Inputs | 8 |
| Input Type | Temperature Probe / RTD |
| Supported Sensor Types | PT100 / PT1000 |
| PT100 Measurement Range | -200 to 600°C |
| PT1000 Measurement Range | -50 to 200°C |
| Analog Input Resolution | 12 bits |
| PT100 LSB Value | 0.2°C |
| PT1000 LSB Value | 0.006°C |
| Input Impedance | ≥ 10 kΩ |
| Sampling Duration | ≤ 160 ms |
| Acquisition Period | 320 ms per channel group + 1 controller cycle |
| Measurement Error (PT100) | ±0.5% FS at 25°C |
| Measurement Error (PT1000) | ±0.3% FS at 25°C |
| Temperature Coefficient | ±0.01% FS/°C |
| Repeat Accuracy | ±0.1°C |
| Total Error (PT100) | 4°C |
| Total Error (PT1000) | 1°C |
| Broken-Wire Detection | Yes |
| Out-of-Range Detection | Yes |
| Isolation Type | Photocoupler |
| External Supply Voltage | 24 V DC |
| Supply Voltage Limits | 19.2–30 V DC |
| Internal Current Consumption | 90 mA at 5 V DC |
| External Current Consumption | ≤ 140 mA at 24 V DC |
| Electrical Connection | 2 Removable Screw Terminal Blocks |
| Mounting Type | DIN Rail / Panel Mounting |
| Dimensions | 90 × 70 × 90 mm |
| Weight | 0.19 kg |
The TM2ARI8LT measures temperature by monitoring the resistance changes of connected PT100 or PT1000 sensors.
An RTD sensor changes its electrical resistance according to temperature. The module measures this resistance-related signal and converts it into a digital temperature value that can be processed by the PLC.
For example, in an industrial heating system, PT100 probes may be installed at different positions inside a heating chamber. As the temperature changes, the resistance of each probe changes accordingly. The TM2ARI8LT acquires these signals through its eight input channels and converts them into digital measurement values.
The PLC program can then compare the measured temperatures with configured setpoints. If a heating zone falls below its target temperature, the controller can activate the corresponding heating output. If a temperature exceeds the permitted operating range, the control program can initiate an alarm or protective action.
The module supports two sensor types:
Each channel must be configured according to the actual sensor type. Selecting PT1000 in the programming software while connecting a PT100 sensor, or vice versa, can produce incorrect measurement results.
A simplified signal path is:
PT100 / PT1000 Sensors → TM2ARI8LT → Resistance Measurement and Conversion → Digital Temperature Values → Modicon PLC → Heating / Cooling Control
The module uses a self-scanning acquisition method. It continuously acquires temperature information from the connected channels and transfers the resulting values to the controller.
Broken-wire and out-of-range detection provide additional diagnostic information. These functions are useful when a sensor becomes disconnected or when the measured temperature exceeds the supported measurement range.
Within the Modicon M238 architecture, the TM2ARI8LT functions as a dedicated temperature acquisition module. It extends the controller’s ability to monitor multiple RTD measurement points through a single expansion module.
The M238 controller executes the main control program, while the TM2ARI8LT handles the acquisition and conversion of temperature signals. This arrangement separates temperature measurement from the main logic-processing function.
A typical temperature control arrangement is:
PT100 / PT1000 Sensors → TM2ARI8LT → Modicon M238 Controller → Heating Elements / Cooling Equipment
| System Component | Function |
|---|---|
| Schneider Electric TM2ARI8LT | Acquires temperature signals from eight PT100/PT1000 sensors |
| Schneider Electric Modicon M238 | Processes temperature values and executes control logic |
| Schneider Electric TM2AMI4LT | Provides additional analog input channels for temperature and other supported signals |
| Schneider Electric TM2ARI8LRJ | Provides eight RTD input channels using RJ11 connections |
| Schneider Electric TM2ARI8HT | Provides temperature-related input channels for NTC/PTC sensors |
| Schneider Electric Heating Controller | Regulates heating equipment according to temperature setpoints |
| Industrial Temperature Sensors | Measures process, equipment, or ambient temperature |
| Cooling System | Reduces process temperature according to controller commands |
The TM2ARI8LT is particularly suitable when multiple temperature measurement points must be integrated into an existing M238-based machine control system.
The TM2ARI8LT is suitable for industrial equipment that requires multi-point temperature monitoring using PT100 or PT1000 resistance temperature detectors.
| Industrial Application | Typical Use |
|---|---|
| Industrial Ovens | Monitoring temperatures at multiple heating zones |
| Heat Treatment Equipment | Measuring furnace and workpiece temperatures |
| Plastic Processing | Monitoring barrel, mold, and heating-zone temperatures |
| Food Processing | Monitoring temperatures in cooking, heating, and processing equipment |
| Chemical Processing | Measuring temperatures in tanks, pipes, and process vessels |
| HVAC Systems | Monitoring temperature at multiple points in heating and cooling equipment |
| Pharmaceutical Equipment | Acquiring temperature measurements in controlled processing systems |
| Industrial Dryers | Monitoring heating chambers and drying zones |
| Water Treatment | Measuring temperatures in tanks and process pipelines |
| Manufacturing Equipment | Monitoring motor, machine, and process temperatures |
When troubleshooting inaccurate temperature readings, first check the selected sensor type and wiring arrangement. PT100 and PT1000 probes have different resistance characteristics, so an incorrect software configuration can result in significant measurement errors.
| Component | Function |
|---|---|
| Schneider Electric Modicon M238 | Main logic controller for the TM2 expansion system |
| Schneider Electric TM2ARI8LT | Eight-channel PT100/PT1000 temperature input module |
| Schneider Electric TM2AMI4LT | Four-channel analog input module supporting temperature and other analog signals |
| Schneider Electric TM2ARI8LRJ | Eight-channel PT100/PT1000 input module with RJ11 connections |
| Schneider Electric TM2ARI8HT | Eight-channel NTC/PTC temperature input module |
| Schneider Electric Modicon Twido | Compatible controller family listed for the module |
| Schneider Electric Advantys OTB | Compatible distributed I/O platform |
| PT100 Temperature Probes | Resistance temperature sensors for industrial measurement |
| PT1000 Temperature Probes | Higher-resistance RTD sensors for temperature acquisition |
| Industrial Heating Equipment | Provides temperature regulation according to PLC commands |
| Model / Product | Product Type | Typical Application |
|---|---|---|
| Schneider TM2ARI8LRJ | Modicon TM2 Analog Input Module | Eight-channel PT100/PT1000 temperature measurement with RJ11 connection |
| Schneider TM2ARI8HT | Modicon TM2 Analog Input Module | Eight-channel NTC/PTC temperature acquisition |
| Schneider TM2AMI4LT | Modicon TM2 Analog Input Module | Four-channel temperature and analog signal acquisition |
| Schneider TM2AMI2LT | Modicon TM2 Analog Input Module | Two-channel thermocouple temperature input |
| Schneider TM2AMI8HT | Modicon TM2 Analog Input Module | Eight-channel voltage/current signal acquisition |
| Schneider TM2ALM3LT | Modicon TM2 Analog Mixed I/O Module | Low-level temperature input and analog output applications |
Yes. The module supports both sensor types. Each input channel must be configured for the corresponding sensor type in the programming software. PT100 supports -200 to 600°C, while PT1000 supports -50 to 200°C.
Both modules provide eight temperature input channels for PT100/PT1000 sensors. The main difference is their electrical connection arrangement. The TM2ARI8LT uses removable screw terminal blocks, whereas the TM2ARI8LRJ uses RJ11 connectors.
Yes. The module supports broken-wire detection, allowing the controller application to identify a disconnected sensor. This diagnostic capability is useful for detecting wiring faults during operation.
No. The TM2ARI8LT is specifically intended for PT100 and PT1000 temperature probes. For standard voltage or current measurements, a compatible high-level analog input module such as the TM2AMI8HT should be selected instead.