Question

Calibration of a current meter for use, in channel flow measurement is done in a

• A. wind tunnel
• B. water tunnel
• C. towing tank
• D. flume

Answer 1

The correct option is C towing tank

The relation between the stream velocity and revolutions per second of the current meter is called the calibration equation. The calibration equation is unique to each instrument and is determined by towing the instrument in a special tank called towing tank.

Towing tank is a long channel containing still water with arrangements for moving a carriage longitudinally over its surface at constant speed. The current meter to be calibrated is mounted on the carriage with the rotating element immersed to a specified depth in the water body in the tank. The carriage is then towed at a predetermined constant speed (v) and the corresponding average value of revolutions per second $\left(N_s\right)$ of the instrument is determined.

This experiment is repeated over the complete range of velocities and a best-fit linear relation in the form of the equation
$v=a{N}_s+b$
where a, b are constants of the current meter.