Plug-in bases make the connection

The system builder can keep a range of these relatively low cost units in stock, only ordering the active units when detailed system configuration requirements have been confirmed. It could be changed if, for example, control units with greater memory capacity are found to be necessary. Furthermore, because the screw-up or quick-connect terminals in the base units are laid out below the active units, the terminals provide easy access for test probes. The base units may either be DIN rail mounted or screwed to a panel, and clicked together. The PLCs are available with three different CPUs: PM571 (micro), PM581 (mini) and PM591 (midi). All units have the same physical size and plug into the same terminal base units. The PM571 has a memory of 64kbits, while the PM591 has 4MB. S500 I/O modules provide extra expansion options including decentralised expansion. The module heads are fieldbus neutral and can be set up to use Profibus DP, CANopen, DeviceNet, Modbus or CS31, by using ABB’s fieldbus plug. The AC500 can also be accessed remotely from a PC via Ethernet or serial networks. Operation is simplified by using an LCD display that can help users to identify and locate specific problems via on-screen diagnostic codes. Other features include an operator keypad, two integrated serial interfaces, and an SD card to download or upload data, such as firmware updates or programming codes, without the use of a PC. Data can also be written to and from the SD card to enable data logging.