The Allen-Bradley 1775-AD1 is the chassis door (with a control panel) for the main chassis (catalog number 1775-A1) of the PLC-3 programmable controller system. The PLC-3 is a modular, field-expandable controller which supports multiple processors. It is engineered for large-scale and complex processes. A PLC-3 system can have a maximum of eight components including the main chassis, front panel, main processor, power supply, expansion system, memory modules, and the industrial terminal. The main chassis (1775-A1) for the PLC-3 houses the different controller modules. It provides 6 module slots and the front panel. The primary functions of the main chassis include protecting the PLC-3 components, providing air circulation, protecting against contaminants and radio-frequency interference (RFI), and displaying the status of the different modules.

The front panel on the chassis door (1775-AD1) contains a keyboard, a 16-character display, a keyswitch and status indicators. The keypad can be used to program the PLC and access the data table. The display enables system monitoring via status/diagnostic messages. The keyswitch provides selectable memory access and the status indicators facilitate troubleshooting by displaying the system status. The peripheral communication channel on the front panel enables connection to an industrial terminal. The monitoring, editing, and loading of program instructions can be carried out through the industrial terminal. The working temperature range for the PLC-3 system and the 1775-AD1 door is 32 -140 °F (0 – 60 °C). The 1775-AD1 and its host’s optimal operation requires relative humidity to be in the 5 – 95% range.