A current meter is a flow measuring device to measure the flow by mechanical or electrical means.
To Measure the Average Velocity of water flow, Different Methods can be used in hydraulics engineering. Out of that Pitot tube is already covered in the below post.
Read: Important Tube Gauges Which Are Used to Measure Fluid Pressure
Here I will cover the “Current Meter” which is used to Measure the Average Velocity of Flow.
This Average Velocity of Flow is required to Measure the River Discharge.
So, here are the details about the Current Meter
It consists of a Wheel containing Blades or Cups which are rotated by the Flowing Water.
An Electric Current is supplied to the Wheel by means of Wire.
A Rotation of the Wheel makes and breaks the Electric Circuit, so it causes an Electric Bell to Ring.
Hence the Velocity of Flowing Water is obtained by counting the ringing of the Bell, and the Rotation of the Wheel.
The Current Meter is suspended by means of a fine cable and lowered to the required Depth.
Hence the Current Meter is free to move about its Horizontal and Vertical Axis.
So that it can adjust itself to the Direction of Water Flow.
Rating of Current Meter
So, the process of obtaining the relationship between the number of Electric Signals, Transmitted from the Current Meter in unit time, and the Velocity of Flowing Water, Flow past the Meter is known as the Rating of the 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. It should happen after each run and the beginning of the next.
02) The Current Meter must not be allowed to approach too closely the sides or bottom of the Rating Channel.
03) The Rating Channel should not be less than 2 meters wide and 1.5 meters deep. It should be long enough to permit a clear run at a Constant Speed of 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 the Field.
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