ABB AI820 S800 I/O Differential Analog Input Module

Configured for differential analog signal acquisition in ABB System 800xA and S800 I/O systems, the ABB AI820 (AI820 Analog Input Module, Article Number 3BSE008544R1) provides direct physical/electrical execution across four bipolar current or voltage channels. The unit converts +/-20 mA or +/-10 V field inputs into 12-bit digital values, distributing external 24 VDC transmitter power through extended Module Termination Units (MTUs) to direct 2-wire field instruments. Onboard current-sensing circuits feature 5 W rated 250 Ohm resistors to protect single channels against accidental 30 VDC overvoltage faults.

Hardware Specifications

Deterministic ModuleBus Execution and Input Overvoltage Protection

The AI820 transmits acquired process image data over the backplane using deterministic backplane bus communication velocity, achieving complete input loop conversion cycles within 1.5 ms. Firmware flash compatibility ensures seamless communication synchronization with cluster controllers across the S800 backplane. Built-in thermal dissipation limits on the 250 Ohm current sense resistors withstand temporary 24 VDC cross-connection events, while groupwise galvanic isolation isolates field signal ground loops from sensitive ModuleBus digital components.

Frequently Asked Questions

Q: How does the AI820 protect its input circuitry if 24 VDC loop power is accidentally miswired to a current input?

A: Each current input relies on robust 5 W rated 250 Ohm sense resistors designed to absorb temporary 30 VDC normal mode overvoltage conditions on a single channel without destroying the input stage.

Q: Are transmitter power supply terminals on the AI820 module current-limited?

A: No. When distributing process power to 2-wire transmitters via extended MTU baseplates, the transmitter power terminals carry no internal current limiting and must rely on external power supply protection.

Q: Can channels on the AI820 be configured independently for current or voltage measurement?

A: Yes. Each of the four differential channels can be individually selected for current (-20 mA to +20 mA) or voltage (-10 V to +10 V) operation in software.

Field Installation Guidelines

Mount the S800 terminal unit onto a standard 35 mm DIN rail, verifying that the integrated grounding clip maintains low-impedance contact with an unpainted metal section of the rail. Insert the AI820 module straight into the MTU guide slots, pressing firmly until the locking latches secure the module in place.

Wire signal leads to the correct differential input terminals, paying strict attention to polarity for bipolar voltage and current loops. Connect shielded cables to the main ground bar via low-impedance grounding clamps. When powering 2-wire field transmitters directly from the module termination unit, ensure the external 24 VDC process power supply incorporates dedicated branch fusing. Keep at least 50 mm of vertical ventilation space above and below the module enclosure for natural thermal dissipation up to +55 deg C ambient operating limits.