Mechanical Current Meter – STM Flowmeter

Mechanical instrument for measuring velocity and flow, for example through a plankton net or a concrete channel.

Main components

• Propeller (rotor)
  Helical shape, made of metal or composite material. Its rotation speed is proportional to the water velocity.

• High-precision shaft and bearing
  Minimize friction to ensure accurate measurements even at low velocities.

• Current meter body (rod / support)
  Allows immersion at a precise depth. Can be mounted on a graduated rod or suspension cable.

• Rotation sensor / pulse generator
  Each full turn produces an electrical pulse (reed switch, induction, or embedded magnet), counted by:

  • an electromechanical counter,

  • a portable logger,

  • or an STM measurement unit.

• STM calibration table
  Provides the pulse ↔ velocity relation to obtain the accurate water velocity (m/s).

Operation

1. The current meter is placed in the flow, usually horizontally.

2. The current drives the propeller’s rotation.

3. The STM system converts the number of rotations into instantaneous velocity (m/s) using the calibration curve.

4. Multiplying average velocity by the wet cross-section gives the discharge.

Typical specifications

• Velocity range: ~0.03 to 5 m/s

• Accuracy: ±1–2 %

• Robustness: suitable for field measurements

• Passive operation: no complex electronics, highly reliable

Applications

• Velocity measurement for river discharge calculations

• Hydrodynamic monitoring of ponds and drained reservoirs

• Flow studies in aquaculture systems

• Monitoring of pumping, drainage, and irrigation flows