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Introduction
1
1.0 INTRODUCTION
The Liebert AC4 is ideal for coordinated control of systems with redundant equipment, such as
multiple environmental units or pumps. When the AC4 controller detects an alarm in an operating
device, the AC4 enables a standby device and controls the device in alarm as configured, either
leaving that device operating or disabling it.
The AC4 controller can also balance usage of devices by rotating units through Operating and
Standby modes according to a user-defined schedule. This helps keep redundant equipment operating
efficiently and only when needed. The AC4 can perform routine testing of standby devices and alert
personnel if a standby device fails an operating test and requires attention.
Another capability of the AC4 is monitoring the status of connected devices and keeping personnel
apprised through local alarming.
The AC4 controller can interface with anything that closes an electrical contact. To improve process
efficiency and troubleshooting, the controller tracks data in two types of logs: alarm and event. The
AC4 has a local LCD interface and an RS232 interface.
When an alarm condition arises, the AC4 displays alarm information, sounds an audible alarm,
changes the state of the common alarm relay and turns connected devices on or off according to user
configuration. See 1.5 - Typical Configuration for a more detailed example.
1.1 Methods of Viewing and Configuring the AC4
The AC4 features access through two interfaces that allow users to configure the unit, silence alarms,
back up logs, and perform many other functions to keep a large or small operation running smoothly
and safely.
• LCD—liquid crystal display on the front of the panel
• Service Terminal Interface—accessible via a computer connected directly to an RS232 port
These interfaces permit easy access and configuration of the AC4, allowing users to view data, silence
alarms and have full access to information stored in the controller, including logs of alarms and
events.
1.2 Data Logs
The two types of data logs—alarm history and event history—can be viewed on the LCD on the front
of the AC4 or the Service Terminal Interface. The logs may also be downloaded to a computer through
the Service Terminal Interface.
1.3 Available Alarms
The alarms available with the AC4 are:
• Discrete input alarm (for each digital input)
• Loss of power
• No standby available
• Standby device failed
• No restart available