Measuring the Rate of Flow

Introduction:

Measuring the rate of flow is one of the most vital parts in most of the plants. In some plants the accurate measurement of flow is so important that it can makes a difference of profit or loss. Apart from this inaccurate flow measurement can also lead to various disastrous consequences.

In most of the cases the flow rate of the liquid is measured by the determining the velocity or change in kinetic energy of the fluid. As the area of the pipe remains constant generally we can write,

Q=V x A

Where Q= liquid flow through the pipe.

There are various types of method to measure the flow. As example,

1. Magnetic flow measurement.

2. Turbine flow measurement.

3. Pitot tube flow measurement.

Among these the turbine flow measurement is discussed below.

Turbine flow measurement:

The basic construction of turbine flow meters includes a bladed turbine rotor which is axially suspended in the pipe. When the fluid flows through the pipe, it causes the rotor to spin on its axis at a speed which is proportional to the velocity of the fluid. There are gears, photoelectric cell or magnetic pickup installed on the outside of the flow tube or the meter body, adjacent to the perimeter of the rotor whose job is to sense the passage of each rotor

Fig: Turbine flow measurement

There are different equipment in the turbine flow measurement. But there are 4 major parts in the flow measurement. These are,

1) Turbine

2) Bearing

3) Preamplifier.

4) Signal reception and display.

A pick-up sensor is mounted above the rotor. We supply our standard Turbine flow meters with either an inductance type pick-up sensor or a Hall-effect sensor. The difference is that the Inductance type sensor generates a voltage pulse each time a rotor blade passes by. Depending on the type of signal receiving instrument a pre-amplifier may be needed. The Hall-effect sensor provides a square wave output each time a blade passes by and has a built in pre-amplifier. The Hall-effect sensor also produces less magnetic drag on the rotor and is more suitable for lower flow rates. The pick-up sensor produces pulses as soon as the rotor blades pass by, this provides an extremely fast reaction time making this type of flow meter highly suitable for batching applications. All Turbine Flow Meters come with very small variations from the manufacturing process. As such, they all need to be calibrated individually. The pulses generated by the pick-up sensor represents pulses per unit volume, also referred to as the k-factor. All of our Flow Meters are supplied with individual calibration certificates and k-factor.

Application:

1. Superheated steam.

2. Liquid flow metering, particularly fluids with lubricating properties.

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