Explain how a voltage divider scales a sensor signal for a PLC input.

• A. A voltage divider reduces a higher sensor voltage to a safe, readable level by using two resistors in series whose ratio sets the output voltage.
• B. A voltage divider increases the sensor voltage to maximize PLC input range.
• C. A voltage divider is used to filter EMI.
• D. A voltage divider stores energy for the PLC.

Answer: (A)

The idea behind using a voltage divider is to attenuate a sensor’s voltage to a level the PLC can safely read. It uses two resistors in series between the sensor output and ground, and the junction between them provides a fraction of the sensor voltage. That fraction is set by the resistor ratio, giving Vout = Vin × (R2/(R1+R2)). This lets a higher sensor voltage be scaled down to the PLC’s input range (for example, 0–5 V or 0–10 V) without amplifying the signal. It’s a passive attenuation, so it won’t store energy or actively filter EMI by itself; if EMI filtering or energy storage is needed, separate components would be added. The PLC input’s impedance matters: if the input draws significant current or loads the divider, the ratio can shift, so you choose resistor values that keep the divider’s loading negligible or add buffering if needed.