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How Ultrasonic Flow meter works | Ultrasonic Flow meter working

This page describes working of ultrasonic flow meter used for water and gas flow rate measurement. It mentions advantages and disadvantages ultrasonic flow meter.

Introduction:
Ultrasonic waves use frequency from 20 KHz to 200 KHz range which are not audible to the human beings. They are used in various applications such as cleaning, distance measurement, welding, cutting of hard materials, medicine, communication, thermal effect, flaw detection etc.

Water meter is a device which measures volume of water flowing through the pipe line. These meters are installed in residential and commercial buildings to measure their water usage. Accordingly bills are generated by the respective water supply board.

How Ultrasonic flow meter works ?

Water meters measure flow of water in cubic meters (i.e. m3). Some meters display rate of flow in addition to total water usage. There are various types of water meters based on their flow measurement method and construction. The common types of water meters include mechanical meter, electromagnetic water meter and ultrasonic water meter.

Ultrasonic Flow Meter

Ultrasonic flow meter can be used as ultrasonic water meter, ultrasonic heat meter and ultrasonic gas meter. Ultrasonic flow meter uses ultrasonic transducer in order to send ultrasonic sound waves through the pipe carrying fluid. The system consists of microcontroller which determines velocity and translate the velocity into water volume or flow rate.

The ultrasonic sensors are usually attached outside of the pipe. Ultrasonic flow meters are mainly of two types viz. transit time transducer based and doppler transducer based. Both of these ultrasonic flow meters measure flow rate using sensors clamped outside of the pipe. Both uses ultrasonic transducer which is a piezo-electric crystal having size of a coin.

When electrical energy is applied to one of these crystals, it emits ultrasonic beams approx. at 5 degree wide angle which can easily pierce through the wall of pipe.The returning echo impacts the second crystal mounted on pipe which creates electrical energy.

Transit time transducer based : It uses pair of transducers each having piezo-electric crystal. In this type, one transducer transmits sound waves while the other receives them. The transit time flow meter measures time duration from emission of pulses till their reception. Both upstream and downstream time measurements are compared using specifically developed algorithm to determine flow rate. The transit flow meter works with clean liquids such as water, oils and chemicals.

Doppler transducer based : In this type, sound waves at particular frequencies are transmitted by one sensor and received by the other sensor. Due to fluid in motion, frequency gets altered. This frequency shift is directly proportional to velocity of fluid. Specifically developed algorithm is used by ultrasonic flow meter manufacturers to determine flow rate. Doppler flow meter works in dirty or aerated liquids.

Maxim Integrated Products Inc. has developed components for ultrasonic flow meter design. The major components include MAX35101 (time to digital converter) and dual SPST switch (MAX 4721). MAX35101 measures low flow with low power consumption. It houses ultrasonic piezoelectric transducers, SPI interface etc. Other parts include microcontroller, LCD, ultrasonic sensors etc.

Benefits or advantages of Ultrasonic flow meter

Following are the benefits or advantages of Ultrasonic flow meter:
➨It offers very accurate flow measurement for billing as well as leak detection.
➨It consumes less power and hence battery will last for longer duration.
➨It is available at lower cost.
➨No external power sources are required for its operation.
➨Long term stability and accuracy over wide range of conditions.
➨It is highly reliable and hence minimum maintenance is needed.
➨Modern flow meter houses GSM/GPRS or other wireless technologies to transfer the data to remote stations.

Drawbacks or disadvantages of Ultrasonic flow meter

Following are the drawbacks or disadvantages of Ultrasonic flow meter:
➨Pipe walls should be clean and dust free to achieve better results.
➨The accurate flow measurement pre-requisite is fluid media must conduct sonic energy and pipe should be full.



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