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Table of Contents

What is circulate units?

Continuity of flow equation

Common circulate unit metering strategies in open channels

Eyeball methodology

Flow depth (Manning)

Main equipment

Surface Velocity Meters

Transport time meters

Flow unit measurement strategies in full tube functions

Venturi meters

Magnetic flowmeter

Turbine flowmeter

Conclusion

What is flow units?

Flow rate is the amount of fluid that passes through a unit of time. In water sources, move is usually measured in cubic feet per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or a wide selection of different models. The measurement of water useful resource move is important for applications corresponding to system control, billing, design and many different applications. There are a number of ways to measure circulate in a water resource system. This article outlines some of the extra frequent strategies of flow measurement and offers some useful information about circulate units measurement.
Continuity of circulate equation

For water flowing in a pipe underneath steady-state circumstances (i.e., not varying with time), continuity signifies that water flowing into one finish of the pipe should circulate out of the other finish. This also implies that the circulate in the pipe is the same at any point along the size of the pipe. The continuity equation can be expressed as

Flow = Velocity * Area

The idea of continuity in steady state situations results in the product of velocity * area being equal to a constant at any level in the pipe. This is a helpful precept for making flow measurements, as proven beneath.
This is an example of utilizing the continuity equation to calculate move. Velocity is measured at 10 toes per second and the cross-sectional space of the circulate is measured at 10 square ft. Flow price = 10 ft per second * 10 sq. ft = one hundred cubic ft per second.
Common circulate unit metering strategies in open channels

Eyeball methodology

It is sometimes useful to estimate the move velocity and cross-sectional area by eye and then multiply the move velocity by the world to acquire the circulate velocity (continuity equation). เพรสเชอร์เกจ or tape measure can be used to enhance the accuracy of cross-sectional space measurements, and a stopwatch can be used to improve velocity measurements by timing floating debris shifting a set distance. The eyeball method can be utilized to estimate flow when solely an “order of magnitude” of circulate is required or when the flow price is simply too low to be measured with a circulate meter.
Flow depth (Manning)

When the channel cross-sectional space and channel slope are known and uniform flow circumstances exist, the Manning’s equation can be utilized to calculate circulate by measuring depth only. The Manning’s equation is an empirical equation that describes the relationship between circulate fee in an open channel beneath uniform circulate conditions and depth, slope and channel friction coefficient (Manning’s n). Uniform move signifies that depth doesn’t differ with the length of the conduit or channel. Flow measurements using Manning’s equation for depth aren’t relevant to progressively changing flow conditions, similar to backwater conditions upstream of a dam or weir.
The depth circulate methodology of circulate measurement is extra correct than the “eyeball” technique. The main problem with depth-only move measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform move situations. This method is usually used with ultrasonic flow meters to estimate the flow of a river by measuring only the water degree of the river. Often in these causes, the river level/flow relationship is developed with the help of complicated river hydraulic models to account for complex channel geometry and channel friction situations.
Main gear

The main system is used to measure circulate in open channels, utilizing structures such as flumes, weirs or dams, to measure circulate by measuring depth. The measured depth can then be converted to a flow price utilizing an equation or rated curve equation.
Primary gadgets work by forcing the flow through a path of crucial depth, for instance on the prime of a weir or on the throat of a flume. In technical phrases, the crucial depth is defined because the depth of the minimal particular power state that leads to a specific discharge. In apply, this minimal state of power means that just one move corresponds to the important depth. Therefore, measuring only the depth produces a measurement of the corresponding flux and is therefore called a “primary” gadget.
Primary devices are a really handy methodology of flow measurement as a result of the depth could be measured from above the circulate without the necessity to insert a sensor within the water. This makes main move meters more dependable and simpler to keep up. A disadvantage of primary gadgets is that they’ll cause head loss and backwater within the system. Primary gadgets are often thought-about to be probably the most correct method of measuring open channel flow.
Surface Velocity Meters

An space velocity meter is an open channel flow meter that measures move by making two separate measurements of depth and velocity. The depth is transformed to a cross-sectional space using the geometry of the pipe or channel. The move rate is then calculated by multiplying the move space by the velocity utilizing the continuity equation, therefore the identify “AV meter”. Velocity is usually measured utilizing a Doppler sensor, which displays ultrasound waves back from particles within the fluid and makes use of the Doppler shift in the reflected sound sign to estimate velocity. Some AV meters measure floor velocity optically to estimate velocity.
AV meters are often used to measure open channel move in sewers because the probes are comparatively small and they can be put in in current sewer pipes without inflicting important head loss in the pipe. This also permits them to be used for temporary or short-term circulate metering applications for sewer studies. one drawback of AV meters is that the sensor should be put in within the fluid. In sewers, this requires frequent upkeep to clean the sensor. AV meters are often thought-about much less accurate than major circulate meters as a result of primary gadgets only have to measure depth and depth measurements are extra correct than velocity measurements.
Transport time meters

Transport time meters had been developed in the oil industry to precisely measure move in massive pipelines. They have been used with some success for open channel circulate in water metering purposes. Transport time meters also use ultrasound like Doppler meters, but as a substitute of bouncing the sound waves off particles in the water like Doppler flow meters, they send ultrasound waves between two sensors separated from each other by a certain distance alongside the length of the pipe and uses the transmission time of the sound waves to calculate the velocity of the water move. Because the speed of sound in the water is understood, the speed of the water may be calculated based mostly on the offset in ultrasonic wave transmission time that occurs due to the pace of the water.
Transmission time meters could be expensive relative to Doppler flow meters as a result of many sensors and sophisticated set up concerned. They can be extra correct due to the capability to split the move into horizontal cross sections and measure the speed of each section.
Flow unit measurement strategies in full tube purposes

Venturi meters

Venturi circulate meters use the Venturi effect to measure flow in a full or pressurized pipe by utilizing the converging part of the pipe to restrict the move. According to the continuity equation, the cross-sectional area of the converging part is small and subsequently the rate is larger within the throat. Due to power conservation and Bernoulli’s principle, larger velocities within the throat end in a drop in throat stress. The move fee can then be determined by measuring the stress drop in the convergent part and calculating the circulate fee utilizing Bernoulli’s equation. Venturi meters are extra frequent in water metering purposes because the stress measurement ports can become clogged in wastewater functions.
Magnetic flowmeter

The electromagnetic flow meter works by making use of a magnetic field to the fluid passing via the pipe. This causes a small electron potential difference that can be measured by the electrode sensor (due to Faraday’s regulation and electromagnetic induction). The magnitude of the electron potential distinction is proportional to the rate of the water, and the continuity equation can then be used to calculate the circulate price.
An advantage of the magnetometer is that the metering part is similar diameter because the adjoining pipe, so the magnetometer causes no further head loss. For essentially the most half, magnetometers are used for full (pressure) pipe purposes, however these days open channel magnetometers can also be used.
Turbine flowmeter

A turbine flow meter is a mechanical move meter that uses a rotating turbine in circulate to measure the move of water in a pipe. The pace of the turbine is proportional to the speed and the circulate rate can then be calculated using the continuity equation. Turbine circulate meters are solely used for water functions as a outcome of potential issues with wastewater solids assortment and clogging generators.
Conclusion

There are some ways to measure circulate. Each method has completely different advantages, disadvantages and accuracy in several purposes.
It is essential to know the characteristics of assorted circulate measurement strategies to help select the best kind of circulate metering on your software or to properly interpret the move measurements of current move meters. Tools like Apure (IoT-based water information analysis) assist to look at measurements collected by flow meters and carry out diagnostics to grasp move meter efficiency and shortly process and analyze the data. Contact us for technical or product service assist.
More articles on move meters:
Mass circulate rate vs volumetric circulate price

Relation between move and pressure

Ultrasonic circulate meter working principle

Difference between flow meter and circulate transmitter
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Table of Contents

What is flow units?

Continuity of flow equation

Common move unit metering strategies in open channels

Eyeball method

Flow depth (Manning)

Main tools

Surface Velocity Meters

Transport time meters

Flow unit measurement strategies in full tube purposes

Venturi meters

Magnetic flowmeter

Turbine flowmeter

Conclusion

What is circulate units?

Flow price is the quantity of fluid that passes through a unit of time. In water sources, flow is usually measured in cubic ft per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or quite a lot of other models. The measurement of water useful resource move is important for purposes corresponding to system management, billing, design and many other applications. There are a quantity of methods to measure flow in a water resource system. This article outlines a variety of the extra common strategies of circulate measurement and supplies some useful details about circulate units measurement.
Continuity of flow equation

For water flowing in a pipe under steady-state situations (i.e., not various with time), continuity signifies that water flowing into one end of the pipe should circulate out of the other finish. This also means that the flow within the pipe is similar at any level along the length of the pipe. The continuity equation could be expressed as

Flow = Velocity * Area

The concept of continuity in regular state situations ends in the product of velocity * space being equal to a constant at any point in the pipe. This is a helpful precept for making move measurements, as shown below.
This is an example of utilizing the continuity equation to calculate circulate. Velocity is measured at 10 feet per second and the cross-sectional area of the flow is measured at 10 square ft. Flow price = 10 ft per second * 10 square feet = a hundred cubic toes per second.
Common circulate unit metering methods in open channels

Eyeball technique

It is typically useful to estimate the move velocity and cross-sectional area by eye and then multiply the flow velocity by the realm to acquire the move velocity (continuity equation). A ruler or tape measure can be utilized to enhance the accuracy of cross-sectional area measurements, and a stopwatch can be used to improve velocity measurements by timing floating debris moving a set distance. The eyeball method can be utilized to estimate move when only an “order of magnitude” of move is required or when the move rate is simply too low to be measured with a circulate meter.
Flow depth (Manning)

When the channel cross-sectional space and channel slope are identified and uniform flow situations exist, the Manning’s equation can be utilized to calculate flow by measuring depth solely. The Manning’s equation is an empirical equation that describes the relationship between move price in an open channel under uniform circulate situations and depth, slope and channel friction coefficient (Manning’s n). Uniform move means that depth does not differ with the size of the conduit or channel. Flow measurements using Manning’s equation for depth aren’t relevant to progressively altering flow conditions, such as backwater situations upstream of a dam or weir.
The depth move technique of circulate measurement is more correct than the “eyeball” method. The primary problem with depth-only flow measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform flow situations. This technique is usually used with ultrasonic move meters to estimate the flow of a river by measuring only the water degree of the river. Often in these causes, the river level/flow relationship is developed with the help of advanced river hydraulic fashions to account for complicated channel geometry and channel friction conditions.
Main gear

The major device is used to measure move in open channels, utilizing structures such as flumes, weirs or dams, to measure circulate by measuring depth. The measured depth can then be converted to a flow fee utilizing an equation or rated curve equation.
Primary devices work by forcing the move through a path of important depth, for instance on the prime of a weir or on the throat of a flume. In technical phrases, the crucial depth is defined because the depth of the minimum particular vitality state that leads to a selected discharge. In follow, this minimum state of power implies that only one flow corresponds to the critical depth. Therefore, measuring only the depth produces a measurement of the corresponding flux and is therefore called a “primary” gadget.
Primary devices are a really handy methodology of circulate measurement because the depth can be measured from above the circulate without the need to insert a sensor in the water. This makes main circulate meters extra reliable and easier to take care of. A drawback of primary gadgets is that they’ll cause head loss and backwater in the system. Primary devices are sometimes thought of to be essentially the most correct technique of measuring open channel circulate.
Surface Velocity Meters

An space velocity meter is an open channel move meter that measures move by making two separate measurements of depth and velocity. The depth is converted to a cross-sectional area utilizing the geometry of the pipe or channel. The flow price is then calculated by multiplying the move space by the speed utilizing the continuity equation, hence the name “AV meter”. Velocity is often measured utilizing a Doppler sensor, which reflects ultrasound waves again from particles in the fluid and makes use of the Doppler shift within the mirrored sound sign to estimate velocity. Some AV meters measure surface velocity optically to estimate velocity.
AV meters are sometimes used to measure open channel flow in sewers as a end result of the probes are comparatively small and they can be installed in current sewer pipes without causing significant head loss in the pipe. This additionally permits them to be used for short-term or short-term flow metering applications for sewer studies. one disadvantage of AV meters is that the sensor have to be put in in the fluid. In sewers, this requires frequent upkeep to clean the sensor. AV meters are often thought-about less accurate than primary flow meters as a result of major units only must measure depth and depth measurements are extra accurate than velocity measurements.
Transport time meters

Transport time meters had been developed within the oil industry to precisely measure flow in massive pipelines. They have been used with some success for open channel move in water metering purposes. Transport time meters additionally use ultrasound like Doppler meters, but as a substitute of bouncing the sound waves off particles within the water like Doppler flow meters, they ship ultrasound waves between two sensors separated from one another by a certain distance alongside the size of the pipe and uses the transmission time of the sound waves to calculate the velocity of the water circulate. Because the pace of sound within the water is known, the speed of the water could be calculated primarily based on the offset in ultrasonic wave transmission time that occurs due to the velocity of the water.
Transmission time meters can be expensive relative to Doppler move meters due to the many sensors and sophisticated installation concerned. They may be more correct due to the capability to separate the flow into horizontal cross sections and measure the speed of every section.
Flow unit measurement strategies in full tube functions

Venturi meters

Venturi circulate meters use the Venturi impact to measure circulate in a full or pressurized pipe by utilizing the converging section of the pipe to restrict the flow. According to the continuity equation, the cross-sectional space of the converging section is small and due to this fact the rate is higher within the throat. Due to power conservation and Bernoulli’s precept, larger velocities within the throat end in a drop in throat strain. The flow fee can then be determined by measuring the pressure drop within the convergent section and calculating the circulate rate utilizing Bernoulli’s equation. Venturi meters are extra widespread in water metering functions because the strain measurement ports can become clogged in wastewater applications.
Magnetic flowmeter

The electromagnetic flow meter works by making use of a magnetic area to the fluid passing by way of the pipe. This causes a small electron potential difference that can be measured by the electrode sensor (due to Faraday’s regulation and electromagnetic induction). The magnitude of the electron potential difference is proportional to the rate of the water, and the continuity equation can then be used to calculate the flow price.
An benefit of the magnetometer is that the metering section is the same diameter because the adjacent pipe, so the magnetometer causes no extra head loss. For essentially the most part, magnetometers are used for full (pressure) pipe purposes, but these days open channel magnetometers can be used.
Turbine flowmeter

A turbine circulate meter is a mechanical move meter that makes use of a rotating turbine in circulate to measure the move of water in a pipe. The velocity of the turbine is proportional to the velocity and the move rate can then be calculated utilizing the continuity equation. Turbine move meters are only used for water functions as a outcome of potential problems with wastewater solids collection and clogging generators.
Conclusion

There are some ways to measure move. Each methodology has completely different benefits, disadvantages and accuracy in several applications.
It is important to know the traits of varied move measurement strategies to help select the right sort of flow metering in your utility or to properly interpret the move measurements of existing move meters. Tools like Apure (IoT-based water data analysis) help to look at measurements collected by circulate meters and perform diagnostics to grasp circulate meter performance and shortly course of and analyze the info. Contact us for technical or product service help.
More articles on circulate meters:
Mass move fee vs volumetric move fee

Relation between move and stress

Ultrasonic circulate meter working principle

Difference between flow meter and circulate transmitter