To Measure Average Velocity of Different Methods can be used in hydraulics engineering.Out of that Floats and Pitot Tube is already covered in earlier posts.In this post I will cover "Current Meter" which is used to Measure Average Velocity of Flow.This Average Velocity of Flow is required to Measure the River Discharge
It consist of a Wheel containing Blades or Cups which are Rotate by the Flowing Water.A Electric Current is supplied to Wheel by means of Wire.
A Rotation of Wheel makes and breaks the Electric Circuit,which causes an Electric Bell to Ring.The Velocity of Flowing Water is obtained by counting the ringing of the Bell,the Rotation at Wheel.
The Current Meter is suspended by means of a fine cable and lowered to the required Depth.The Current Meter is free to move about its Horizontal and Vertical Axis,so that it can Adjust itself with the Direction of Water Flow.
Rating of Current Meter:-
The process of obtaining the relationship between the number of Electric Signals,Transmitted from Current Meter in unit time,and the Velocity of Flowing Water,Flowing past the Meter is known as the Rating of Current Meter
By Rating Curve or Rating Table,we can Directly obtain the Velocity of Water with the corresponding Signals.
Precautions for Rating of Current Meter:-
01)The Water in the Rating Tank must be allowed to come completely to rest,after each run and beginning of the next.
02)The Current Meter must not be allowed to approach too closely to the sides or bottom of the Rating Channel.
03)The Rating Channel should not be less than 2 meter wide and 1.5 meter Deep.It should be long enough to permit a clear run at a Constant Speed for at least 15 meters.
04)The Current Meter should be supported by the same type of Rod or Cable,which is intended to be used during the Velocity observations in Field.