1. Product Overview

Name: 8-Channel RTD Pt100 Analog Input Module
Model: SM_RTD_108i
Series: SUNIX ioSCADA SM Series – Industrial Modbus I/O Modules
Article Number: SM_RTD_108i
Manufacturer: Sunix Group

The SM_RTD_108i is an industrial-grade, 8-channel RTD (Resistance Temperature Detector) analog input module designed for precise temperature measurement and data acquisition in distributed control systems (DCS), programmable logic controllers (PLC), and supervisory control and data acquisition (SCADA) environments. It is part of the SUNIX ioSCADA SM series, which provides modular, high-reliability I/O solutions supporting the Modbus RTU and ASCII protocols over RS-485 communication networks.

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2. Key Features

- Eight Differential RTD Channels: Supports 8 fully isolated differential input channels for high-accuracy temperature measurement.
- Wide Sensor Compatibility: Compatible with Pt100, Pt1000, Cu50, Cu100, and Ni120 RTD types, covering a broad range of industrial sensing applications.
- High Precision and Resolution: 16-bit A/D conversion with 0.1°C resolution and ±0.1°C accuracy for platinum sensors.
- Inherent 3-Wire Compensation: Built-in 3-wire lead compensation ensures accurate readings by automatically correcting for lead resistance.
- Fast Conversion Rate: 140 ms per channel conversion time, suitable for real-time monitoring.
- Robust Electrical Protection: 100 V input protection and 3 kV isolation between communication, logic, and field sides.
- Industrial Communication: Standard Modbus RTU/ASCII protocol over RS-485 (3-wire) interface, supporting up to 63 modules on a single network without a repeater.
- High Noise Immunity: Meets IEC61000-4-4 EFT Level 3 and IEC61000-4-2 ESD Level 3 standards for electromagnetic compatibility.
- User-Friendly Indicators: LED indicators for power, communication (TX/RX), I/O activity, and termination resistor status.
- Flexible Mounting: DIN-rail mountable with compact dimensions (132 × 125 × 47.5 mm).
- Wide Operating Range: Designed for harsh industrial environments with an operating temperature range of -30°C to +75°C.
- Dual Watchdog System: Hardware and communication watchdogs ensure continuous operation and fail-safe behavior.

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3. Technical Specifications

Electrical and Measurement Parameters
- Input Channels: 8 differential
- Input Types: Pt100, Pt1000, Cu50, Cu100, Ni120
- Excitation Current: 200 µA DC typical (all types)
- Lead-Wire Compensation: Inherent for 3-wire RTD
- Maximum Lead Resistance:
- Pt sensors: 25 Ω per lead
- Cu sensors: 10 Ω per lead
- Ni sensors: 20 Ω per lead
- Resolution: 16-bit (1 part in 32,000)
- Accuracy: ±0.1°C for Pt sensors, ±0.2°C for Ni/Cu sensors
- Conversion Time: 140 ms per channel
- Input Filter Bandwidth: -3 dB at 1.5 Hz (typical)
- Noise Rejection:
- Normal mode: 60 dB @ 60 Hz
- Common mode: 90 dB @ 60 Hz
- Ambient Temperature Effect: Better than ±0.005% of input span per °C or ±1.0 µV/°C

Input Range and Accuracy Table
| Sensor Type | Alpha | Range (°C) | Resolution | Accuracy |
|--------------|--------|------------|-------------|-----------|
| Pt100 (0.00385–0.003926) | — | -200 to 850 | 0.1°C | ±0.1°C |
| Pt200 / Pt500 | 0.00385 | -200 to 850 | 0.1°C | ±0.1°C |
| Pt1000 (0.00375–0.00385) | — | -200 to 850 | 0.1°C | ±0.1°C |
| Ni120 | 0.00672 | -80 to 260 | 0.1°C | ±0.2°C |
| Cu100 / Cu50 | 0.00427 | -100 to 260 | 0.1°C | ±0.2°C |

Electrical and Power
- Power Supply: 10–30 VDC
- Typical Current Consumption: 0.1266 A @ 24 VDC
- Isolation Voltage: 3000 Vrms (RS-485, field-to-logic, and channel-to-channel)
- Overvoltage Protection: 70 VDC/Vp-p
- Input Protection: 100 V (voltage input)

Physical Characteristics
- Dimensions: 132 × 125 × 47.5 mm
- Mounting: DIN-rail
- Weight: Approx. 0.4 kg
- Material: Industrial-grade ABS enclosure

Environmental Conditions
- Operating Temperature: -30°C to +75°C
- Storage Temperature: -45°C to +85°C
- Relative Humidity: 5–90%, non-condensing

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4. Functionality

The SM_RTD_108i functions as a high-precision RTD input module for temperature measurement and data acquisition in industrial automation systems. Each of its eight channels can independently measure temperature from various RTD types, converting resistance values into temperature readings with linearization and digital filtering.

Operation Principle:
- The module excites each RTD sensor with a constant 200 µA current.
- The resulting voltage drop across the RTD is measured and converted to a digital value using a 16-bit ADC.
- The internal microcontroller linearizes the signal according to the selected RTD type and outputs the temperature in 0.1°C increments.
- Built-in 3-wire compensation automatically corrects for lead resistance, ensuring accurate readings even with long cable runs.

Use Cases and Applications:
- Industrial process temperature monitoring
- Power plant and steel manufacturing temperature control
- Petrochemical and refinery process automation
- Environmental and HVAC monitoring systems
- SCADA and DCS distributed I/O networks

Compatibility:
- Fully compatible with Modbus RTU and ASCII master devices such as PLCs, PACs, DCS controllers, and SCADA software (e.g., LabView, Wonderware, Citect, Intellution).

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5. Components & Accessories

Included Items:
- SM_RTD_108i module
- DIN-rail mounting accessory
- Installation CD with ioCFG configuration software
- Quick installation guide

Optional Accessories:
- RS-232/RS-485 isolation converter
- RS-485 repeater (for networks exceeding 1200 m)
- Shielded twisted-pair communication cables (16–24 AWG)

Connectors:
- Removable terminal blocks for power, communication, and I/O
- RS-485 (3-wire): Data+, Data–, COM

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6. Installation & Setup

Requirements:
- Power supply: 10–30 VDC industrial-grade, compliant with IEC-61000-4-4 2 kV surge protection
- Host system: PC, PLC, or SCADA with RS-485 interface
- Configuration software: ioCFG (Windows-based utility)

Mounting Options:
- DIN-rail (horizontal or vertical orientation)
- Panel mounting (optional accessory)

Configuration:
- DIP switches for baud rate, Modbus address, and protocol selection (RTU/ASCII)
- Default settings:
- Baud rate: 115.2 kbps
- Address: 1
- Parity: None, 8 data bits, 1 stop bit
- Up to 63 modules can be connected on a single RS-485 bus (4000 ft maximum without repeater).

LED Indicators:
- PWR: Power status
- RX/TX: Communication activity
- IO_ACC: I/O access status
- Rt_ON: RS-485 termination resistor status

Reset to Factory Defaults:
- Via DIP switch (SW-2, pin 7 INIT) procedure:
1. Power off the module
2. Set INIT switch ON
3. Power on
4. Set INIT OFF within 5 seconds

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7. Performance & Capabilities

- Measurement Speed: 140 ms per channel (approx. 1.12 s for all 8 channels)
- Resolution: 0.1°C
- Accuracy: ±0.1°C for Pt sensors, ±0.2°C for Ni/Cu sensors
- Noise Rejection: 60 dB normal mode, 90 dB common mode
- Isolation: 3-way isolation (RS-485, logic, and field)
- Network Capacity: Up to 63 modules per RS-485 segment
- Communication Speed: 1200–115200 bps (default 115200 bps)
- Reliability: Dual watchdog (hardware and communication) ensures continuous operation even under communication loss or hardware fault.
- Fail-Safe Operation: In case of communication failure, outputs revert to user-defined safe states.

Limitations:
- Conversion time limits ultra-fast sampling applications.
- Designed for RTD sensors only (not thermocouples or thermistors).
- Requires proper grounding and shielding for optimal noise immunity.

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8. Standards & Compliance

Communication Standards:
- Modbus RTU/ASCII over RS-485 (3-wire)
- Supports Modbus function codes: 01, 02, 03, 04, 05, 06, 08, 15, 16, 17

Electrical and Safety Standards:
- Isolation Voltage: 3000 Vrms (RS-485, field-to-logic, channel-to-channel)
- Overvoltage Protection: 70 VDC/Vp-p
- Surge Immunity: IEC61000-4-5 (0.5 kV)
- EFT Immunity: IEC61000-4-4 Level 3 (power and signal lines)
- ESD Immunity: IEC61000-4-2 Level 3 (8 kV air, 4 kV contact)
- CE Compliant

Environmental Compliance:
- Operating temperature: -30°C to +75°C
- Storage temperature: -45°C to +85°C
- Humidity: 5–90%, non-condensing

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9. Additional Information

Warranty:
- 2 years from delivery or 1 year after installation (whichever comes first)
- Covers manufacturing defects under normal operating conditions
- Excludes damage from improper installation, misuse, or environmental conditions outside specifications

Support & Maintenance:
- Free ioCFG configuration software for Windows
- Firmware updates available through Sunix technical support
- RMA process available for defective units (requires authorization code and problem description)
- Typical repair cost after warranty: ~25% of product price

Service Policy:
- Free repair, testing, and adjustment during warranty period (shipping costs borne by customer)
- Post-warranty repairs subject to quotation; customer notified if cost exceeds 50% of product value

Documentation & Updates:
- User manual and Modbus register maps included on installation CD
- Sunix reserves the right to modify specifications without prior notice

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Summary

The Sunix SM_RTD_108i is a robust, high-precision RTD input module engineered for industrial automation and SCADA systems requiring accurate temperature measurement and reliable communication. With its 16-bit resolution, 3-way isolation, and Modbus RTU/ASCII compatibility, it integrates seamlessly into distributed control networks. Its rugged design, wide operating temperature range, and compliance with IEC and CE standards make it ideal for demanding environments such as power generation, steel manufacturing, and petrochemical processing.

The module’s combination of precision, configurability, and industrial durability positions it as a versatile solution for temperature monitoring and control in modern automation infrastructures.