Description

Yokogawa ACM22 RS-422/RS-485 Communication Module

The Yokogawa ACM22, also cataloged as the ACM22 Communication Module, operates as a dedicated hardware component for serial data interfacing between Field Control Stations and peripheral devices within CENTUM CS 1000 / CS 3000 platforms.

Hardware Specifications

Parameter	Specification
ModelBrand	ACM22
Origin	Japan
Weight	0.50 kg
Dimensions	Nest-mount, 1 slot
OperatingTemp	0 to 55 degC
PowerConsumption	Max. 1.2 A at 5.0 VDC (backplane supplied)
Number of Ports	2 (independent, RS-422/RS-485 selectable)
Communication Mode	Half-Duplex, 2-wire or 4-wire
Supported Baud Rates	1200 / 2400 / 4800 / 9600 / 19200 / 38400 bps
Maximum Transmission Distance	Up to 1,200 m per port
Maximum Connected Nodes	31 slave devices per port (RS-485 mode)
Transmission Media	Shielded Twisted Pair (STP) cable
Isolation Voltage	500 V AC between comm circuit and internal logic
Connection Interface	Terminal block or D-sub connector (per nest plate suffix)
Synchronization	Asynchronous / Start-Stop

DCS Integration Features

The ACM22 provides channel-to-channel isolation to prevent interference between serial lines. It supports 4-20 mA HART loop protocol integration when connected to analog I/O subsystems. Cold junction compensation (CJc) circuitry ensures minimal thermal-induced offset when communicating with temperature-sensitive instruments.

Frequently Asked Questions

Q: Can the ACM22 be hot-swapped while the FCS is powered?
A: No. The module must be inserted or removed only with the nest power off to prevent backplane current spikes.

Q: What is the effect of connecting more than 31 devices on an RS-485 port?
A: Exceeding 31 nodes can result in bus reflections, communication errors, or reduced signal integrity.

Q: Are firmware updates required for compatibility with newer CENTUM CS 3000 revisions?
A: The ACM22 is firmware-independent; compatibility relies on nest and FCS backplane versions.

Field Installation Guidelines

• Install in a properly grounded nest slot; avoid shared ground loops with high-current devices.
• Use shielded twisted-pair cables; terminate shields at one end only to prevent circulating currents.
• Set DIP switches or jumpers for RS-422 or RS-485 mode and termination resistor value (100 or 120 ohms).
• Maintain minimum separation from high-frequency switching devices to reduce EMI.
• Verify LED status indicators (Ready, Run, Tx/Rx) after installation for proper line operation.

Specifications

• Brand: Yokogawa

Advantages

• High reliability in industrial environments
• Supports continuous operation
• Compatible with major PLC/DCS systems