Which device would typically be used to input a numeric value into a PLC during configuration?

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

Answer: (B)

Entering a numeric value into a PLC during configuration is easiest when you have a device that can represent individual decimal digits directly. BCD thumbwheels provide this by giving you multiple wheels, each showing a digit from 0 to 9. By setting several wheels, you can compose a multi-digit number exactly as you want it, and the PLC reads those wheels as a binary-coded decimal value. This makes precise parameter entry quick, visible, and hardware-based, which is handy for settings like addresses, time intervals, or counts.

Pushbuttons can be used to change values, but they’re slow and impractical for entering a precise multi-digit number. An indicator lamp is only a display to show a state and cannot input data. A toggle switch offers only two states (on/off), which is insufficient for numeric configuration beyond a single binary choice.

So, BCD thumbwheels are the best fit for directly inputting a numeric value during PLC configuration.