The AI820 is a high-performance, multifunctional differential analog input module, part of the ABB Ability™ System 800xA® hardware family, designed for high-precision signal acquisition in industrial automation and control systems. This module provides 4 fully isolated differential input channels. Each channel can be independently configured as a current or voltage input, supporting various industrial standard signal ranges including ±20 mA, 4…20 mA, ±10 V, 2…10 V, etc., offering strong compatibility and flexibility.
The AI820 employs a differential input design, effectively suppressing common-mode interference and ensuring signal acquisition accuracy and stability in harsh industrial environments. The module features a high-precision analog-to-digital converter with 14-bit resolution plus a sign bit. Combined with low-temperature drift and high noise immunity, it is suitable for various demanding applications such as process control, monitoring systems, and data logging.
The module also integrates power distribution for external two-wire transmitters. When used with Extended Module Termination Units (MTUs), it simplifies field wiring and reduces system integration complexity. All channels are designed with group isolation, ensuring signal safety and system reliability.
2. Key Features and Benefits
| Feature | Description |
| Multi-Signal Type Support | Supports current (-20…+20 mA, 0…20 mA, 4…20 mA) and voltage (-10…+10 V, 0…10 V, 2…10 V, -5…+5 V, 0…5 V, 1…5 V) inputs with excellent compatibility. |
| Differential Input & High Isolation | 4 differential input channels, all channels within a group are isolated from ground. Rated insulation voltage: 50 V. High Common Mode Rejection Ratio (CMRR > 80 dB). |
| High Accuracy & Resolution | 14-bit resolution plus sign bit. Total error ≤ 0.1%. Low temperature drift (Current: 50 ppm/°C, Voltage: 70 ppm/°C). |
| Built-in Protection Mechanisms | Input shunt resistors withstand accidental connection up to 30 V DC. The 250 Ω current sense resistors have a 5 W instantaneous overload capability to protect the input circuit. |
| HART Communication Compatibility | The input circuit can carry HART communication signals, supporting integration with smart instruments. |
| External Transmitter Power Supply | The module can distribute 24 V DC power to external two-wire transmitters via the MTU, simplifying wiring. |
| Fast Response | Update cycle for all 4 channels < 26 ms. Input filter rise time: 40 ms. Suitable for fast process signal acquisition. |
| Comprehensive Diagnostics | Front panel equipped with F (Fault), R (Run), and W (Warning) LEDs. Supports module and channel-level status monitoring. |
| Wide Environmental Suitability | Suitable for Class I Div 2 / Zone 2 hazardous locations. Certified by multiple marine classification societies. Operating temperature range: 0…+55°C. |
| Modular Installation | Compatible with various MTUs (TU810, TU812, TU814, TU830, TU833). Flexible installation suitable for compact or extended cabinet layouts. |
3. Functional and Design Description
3.1 Input Channel Configuration
Each channel of the AI820 can be independently configured as a voltage or current input via hardware wiring and software settings. Voltage inputs utilize a high-impedance differential structure to minimize loading effects. Current inputs are converted to voltage signals for measurement via an internal 250 Ω precision resistor. The module supports HART digital signal superposition, making it suitable for smart transmitter systems.
3.2 Isolation and Noise Immunity
All 4 channels are electrically isolated from the ModuleBus and ground as one group, with a rated insulation voltage of 50 V and a dielectric strength of 500 V AC. The high Common Mode Rejection Ratio (≥80 dB) and Normal Mode Rejection Ratio (33 dB) ensure signal integrity even in environments with strong electromagnetic interference.
3.3 Power Supply and Distribution
The module receives 24 V DC power from the ModuleBus and provides power distribution for external two-wire transmitters. When used with Extended MTUs (e.g., TU830), power can be supplied directly to field instruments without additional terminals. The power supply lines do not have current limiting; protection relies on fuses within the MTU or external circuits.
3.4 Protection Mechanisms
Overvoltage Protection: Current inputs can withstand accidental connection up to 30 V DC. The 250 Ω sense resistors have a 5 W instantaneous overload capability.
Filtering and Stability: Each channel is equipped with a low-pass filter (LPF) with a 40 ms rise time, effectively suppressing high-frequency noise.
Status Monitoring: The module includes internal power supply monitoring and channel diagnostics. Faults are indicated via front panel LEDs and system bus alarms.
3.5 Wiring and MTU Compatibility
The AI820 is compatible with various Module Termination Units, including:
TU830/TU833 Extended MTU: Integrates power distribution and fuses, supporting direct connection of three-wire instruments.
TU810/TU814 Compact MTU: Provides terminals for 24 V process voltage input; requires external power distribution.
TU812 Compact MTU: Features a D-Sub 25-pin connector, suitable for high-density wiring applications.
4. Typical Application Scenarios
The AI820 is suitable for various industrial process control and monitoring systems, including but not limited to:
Process Variable Acquisition: Precise measurement of analog signals such as temperature, pressure, flow, and level.
Energy Management Systems: Monitoring and recording of electrical parameters like voltage, current, and power.
Equipment Condition Monitoring: Signal acquisition from mechanical sensors for vibration, displacement, speed, etc.
Laboratory and Test Benches: Multi-channel, high-precision data acquisition systems.
Hazardous Area Applications: Suitable for environments certified for Class I Div 2 / Zone 2, such as chemical, oil, and gas industries.
5. Installation and Configuration Recommendations
MTU Selection: Choose the appropriate MTU type based on field wiring complexity and power supply requirements.
Grounding and Shielding: It is recommended to use shielded twisted-pair cables and implement single-point grounding on the cabinet side to reduce noise interference.
Power Distribution: When powering multiple two-wire transmitters, calculate the total current and ensure the MTU fuse capacity is sufficient.
Environmental Considerations: In high-temperature or densely packed installations, ensure adequate heat dissipation to keep the module within its rated temperature range.
Software Configuration: Configure each channel's signal type, range, and filter parameters via the System 800xA or corresponding controller platform.
