Which option is not among the three main water meter classifications?

• A. Ultrasonic
• B. Velocity
• C. Compound
• D. Displacement

Answer: (A)

The main concept is that three traditional water meter classifications are displacement, velocity, and compound meters. Displacement meters measure volume by trapping a fixed amount of water and counting cycles as that volume moves through, giving direct flow volume. Velocity meters determine flow rate from how fast the water moves through a flow element and then convert that velocity into a volume. Compound meters blend both approaches to handle a wide range of flow rates, switching between displacement at low flows and velocity at higher flows to maintain accuracy.

Ultrasonic meters operate on a different principle. They use sound waves to measure flow—transit-time or Doppler methods—to infer volume without moving mechanical parts. Because this relies on acoustic measurements rather than the mechanical displacement or velocity-based methods of the three main categories, Ultrasonic is not considered one of the three main classifications.