Fluid Flow Sensors (Flow Sensor)

Flow measurement known since 1732 when Henry Pitot regulate the amount of fluid flowing. In the measurement of fluid necessary to determine the amount and flow velocity vector at a point in the fluid and how the fluid changes from point to point. Measurement of fluid flow or censorship can be classified as follows:
1. Measurement of the quantity
These measurements provide guidance that is comparable to the total quantity that has flowed in a given time. Fluid flows through the primary element in a row in a quantity less isolated by alternately filling and emptying the measuring vessel of known capacity. Quantity measurement are classified according to:
a. Gravimetric gauge or weight measurement
b. Volumetric gauges for liquids
c. Volumetric gauge for gas

2. Measurement of flow rate
The flow rate Q is a function of the pipe area A and the velocity V of the fluid flowing through the pipeline, namely:
Q = AV
but in practice, the speed is uneven, more in the center. So the average measured velocity of liquids or gases may differ from the actual average speed. These symptoms can be corrected as follows:
Q = KAV
where K is a constant for a particular pipe and describes the relationship between average actual speed and the speed measured.

This constant value can be obtained through experimentation. Measurement of flow rate used to measure the velocity of the liquid or gas flowing through the pipe. These measurements are further grouped according to the measured jemis materials, liquid or gas, and according to the properties of the primary elements as follows:
a. Flow rate measurement for liquids:
1) the type of deflection vanes
2) the type of propeller rotation
3) type of helical vane
4) The type of turbine
5) measuring combination
6) magnetic flow meter
7) ultrasonic flow meter
8) the flow meter range (vortex)
9) measuring the vortex (swirl)

b. Measurement of gas flow rate
1) the type of deflection vanes
2) the type of propeller rotation
3) types of thermal

3. Measurement of pressure differential method
Type flow meter is the most widely used is the measurement of differential pressure. In principle, different cross-sectional area of ​​the flow is reduced by that lead to higher speed, thus also raising energy or kinetic energy movement. Since energy can not be created or destroyed (law of energy transfer), the increase in kinetic energy is obtained from the pressure energy change.

More specifically, when the fluid moves through the conductor (pipe) uniform at low speed, then the motion of each particle is generally aligned along the line of the pipe wall. If the flow rate increases, the peak point reached when the random motion of particles becomes more and more complex. Free roughly where this change occurs is called the critical velocity and flow at higher speed level called turbulent and at a lower speed level is called laminar.

Critical velocity also called Reynold numbers, written without

dimensions:
where: D = cross-sectional dimension of the fluid flow, usually diameter
ρ = density of the fluid
V = velocity of fluid
μ = absolute velocity of fluid
The speed limit is critical to the pipe, usually located between 2000 and 2300.

This method of flow measurement can be done in many ways, for example: using a pipe venturi, pitot pipe, orifice plate (small holes), turbine flow meter, rotameter, thermal means, using radio active materials, electromagnetic, sonic and flowmeter ultar gyro. Another way can be developed according to the needs of the process. Discussed in this book is the flow rate sensor is based on the difference in pressure.