For Level measurement, which sensors are used?

• A. Orifice plate, magnetic flow meter
• B. Pressure transducer, piezoelectric sensor
• C. Float switch, ultrasonic, capacitive
• D. Thermocouple, RTD

Answer: (C)

Level sensing relies on methods that determine how high the liquid surface is, using devices that either touch the liquid or measure distance to the surface. A float switch uses a buoyant float that follows the liquid level and actuates a switch or transmitter as the level changes. Ultrasonic sensors send a sound pulse and measure its round-trip time to the surface to calculate distance, providing a non-contact level measurement. Capacitive sensors detect level by changes in capacitance caused by the liquid’s dielectric difference from air, often with probes inserted into the tank or arranged around it.

These approaches cover the common ways to gauge level: mechanical (float), acoustic (ultrasonic), and electrical/dielectric (capacitive). The other options are primarily for measuring something else: orifice plate and magnetic flow meters measure flow rate, while pressure transducers and piezoelectric sensors measure pressure or dynamic signals (not directly the liquid height). Temperature sensors like thermocouples and RTDs are unrelated to level.

So the best choice aligns with typical level measurement methods: float, ultrasonic, and capacitive sensing.