Which device allows an operator to input or change PLC programs?

Which device allows an operator to input or change PLC programs?

• A. Pushbutton
• B. BCD thumbwheels
• C. Indicator lamp
• D. Toggle switch

Answer: (B)

Direct numeric input to a PLC for programming is done with BCD thumbwheels. These devices present decimal digits in binary coded form that the PLC can read as data, allowing an operator to input or modify program parameters or steps directly on the hardware. Pushbuttons, toggle switches, and indicator lamps serve as run-time inputs or status indicators rather than methods to enter or change the program itself. In older PLC setups, BCD thumbwheels provided a straightforward hardware means to load or adjust program data; today, programming is typically done via software, but the principle remains that a device capable of entering or altering program values is the thumbwheel input.

Direct numeric input to a PLC for programming is done with BCD thumbwheels. These devices present decimal digits in binary coded form that the PLC can read as data, allowing an operator to input or modify program parameters or steps directly on the hardware. Pushbuttons, toggle switches, and indicator lamps serve as run-time inputs or status indicators rather than methods to enter or change the program itself. In older PLC setups, BCD thumbwheels provided a straightforward hardware means to load or adjust program data; today, programming is typically done via software, but the principle remains that a device capable of entering or altering program values is the thumbwheel input.