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Flow measurement equipment PDF Print E-mail
Written by Administrator   
Sunday, 09 September 2012 23:00


The purpose of this document is to present different modes of the use of equipment. 

The document transfers experiences gained during many years of equipment handling in different conditions and fields of work, and is in accordance with the training provided in more then 100 water utility

   Measurement Equipment

  General Information on Measurement Equipment

Measurement equipment is used for the measurement of hydraulic parameters in the water systems and it is essentially divided into measurement equipment for flow measurement (flow meters) and measurement equipment for pressure measurement (pressure probes and pressure gauge).  In addition to the equipment for measurement of hydraulic parameters, also used is the auxiliary equipment such as an ultrasonic wall thickness measurement device, measurement wheel for the measurement of pipe length between the probes of the correlator, mobile meter and measuring tape for the measurement of pipe diameter (for the  purpose of calculating the outer diameter of the pipe).  GPS device for the identification of coordinates of interesting positions prior and during the time of the measurement campaign and leak detection can also be considered as a part of measurement equipment. 

The ViKs, at specific points in their systems also have built-in el-magnetic flow meters installed which can also be used during measurements in those areas and should be taken into consideration during the production of the Loss Measurement Plan. 

Pressure measurement equipment is founded on the two types of digital probes with data logger and one type of analog probe making records on measuring tape.

Measurement Equipment for Flow Measurements – Portable Ultrasonic Flow Meter

 Preparing the Device for Measurements

Ultrasonic portable flow meter is used for occasional flow measurements at permanent or temporary measurement points.  It is very easy to perform measurements with this device; however, certain preconditions should be fulfilled in order for the measurement to be accurate.

The device operates on the principle of time difference of ultrasonic signal transmission through the liquids.  This time directly depends on the speed of sound and volumetric flow.

Two probes that are constituent parts of this device operate alternatively as receivers and as transmitters of ultrasonic waves.  The measurement is mostly performed in line with the so-called reflex method when the probes are located on the same side of the pipe, at appropriate distance.  The application of this method depends on the manufacturer and the types of probes and is followed during measurements performed at pipes with diameter up to 200 mm.

Before starting to operate the device, it is necessary to prepare it for measurement in order to avoid interruptions at moments which could endanger the measurement campaign itself.  Therefore it is necessary to check and provide the following:

1. Check and recharge the battery of the device

Batteries for the devices (this refers to all types of equipment) have their useful life which can, depending on the device handling mode, between one and three years.

When the time for battery replacement comes, the battery is being ordered from the manufacturer of the device (more expensive alternative) or, in case we have battery data, we can find on the market (on the internet or alike) a replacement battery with same characteristics which shall be installed by a skilled person (cheaper alternative).

It is important to emphasize that the batteries for the devices are not produced by the companied that produce the devices but that they are being bought on the market or procured by their suppliers.  Apart from that, often batteries of higher capacity than the original batteries can be found on the market; therefore, it is possible to use the device on site for a longer period of time.

Before the beginning of measurement the battery must be fully charged and the device kept connected to the recharger until going to the measurement point where it is to be installed.

If the device is not going to be used for a longer period of time, the battery should be completely emptied, and if possible (with devices which battery is reachable and do not need disassembling) disconnect the battery from the device.

2. Check and set time and date

Setting the time and date on the device before the beginning of measurement should never be forgotten.  In case the number of devices is high, time and date setting should be done simultaneously for all of them in order for all data for data processing to be referring to the same time.

3. Check whether all accessories and appurtenances are given with the device

Additional equipment used with the mobile ultrasonic flow meter includes: ultrasonic probes, cables, gel and connections for pipes.  Without the aforementioned equipment it is not possible to use the ultrasonic flow meter.   In addition to that, there is also some equipment which to a large extent facilitates the measurement and makes it more reliable, and it includes: ultrasonic wall thickness measurement device, measurement tape or mobile meter for the measurement of pipe diameter with the purpose of obtaining precise data on outer diameter, electric or battery powered grinder for the preparations of measurement points on metal pipes, as well as glass paper for the same purpose.

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During the installation of the device it is useful to have a flashlight and paper towel which shall serve multiple purposes (wiping the gel, cleaning the pipes etc).

4. Provide back-up power supply for the device

Based on the data from the measurement plans, for measurements with definite period of duration a back-up power supply must be provided as well as extension cords (take care that the cable is long enough), 12 V accumulator, spare batteries, petrol or solar aggregate for the same purpose.   

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5. Preparation of measurement point and testing the device

If there is a possibility, one day or several hours prior to the beginning of measurement it is good to prepare the measurement point for measurement.  Pipes made of plastic masses are necessary to be well cleaned, while steel and ductile iron pipe points where probes shall be installed must be cleaned until shiny clear. 

By testing the device at the measurement point before the measurement it is possible to avoid problems in reference to the quality of ultrasonic wave transmission through the pipeline and alike. 

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6. Protect the device from bad weather conditions

  • The majority of ultrasonic flow meters is not protected from the bad weather conditions and that should be taken into consideration in order not to cause any permanent damage of the device
  • During measurements in the open space it is necessary to provide adequate protection of the device from precipitation and sun rays
  • Air temperature required during the operation of the ultrasonic flow meter should be between 0 and 50 °C, and between -5 and 50 °C when it is kept on stock
  • During installation on the pipe, ultrasonic meter probes can be partly submerged into the water (in extraordinary situations) and that shall not affect the quality of measurement or safety of the device, but the water level by no means can reach the connector to which the cables are connected
  • Flow meter central processing unit must not get in contact with water, and the best way to protect it is to keep the device in its original, half-closed box, at all times
  • For this purpose different types of covers, stands and umbrellas are being provided, and the best thing to do is definitely to keep the device in measurement or any other vehicle.

7. Secure the device from theft during measurement

During the operation of the device in the open air, when the measurement lasts only for a couple of hours, an operator has to stand by the device.  In addition to the precautionary measures from potential theft, the presence of the operator is also essential so that a continuous control of the operation of the device could be performed.

When the measurements last for a longer period of time, it is essential to plan in advance to physically protect the device by locking the manhole with the device, park the car over the manhole etc.

Selection of the Measurement Point Location for the Installation of Ultrasonic Flow Meter

During the selection of measurement location, the following should be taken into consideration:

1. Location at which the manhole shall be constructed must be dry, and the manhole itself has to be large enough to easily accept the installation of measurementDuring the construction of the manhole for occasional measurements, one should bear in mind that there is enough space for the fixed meter to be installed, should the need arise later on.

2. If possible, the manhole should be located in the vicinity of electric and telephone lines in order for the device to get easily supplied with electricity and in order to potentially perform electronic remote data transfer from the meter into the PC where the data would be stored.

3. Manhole location must be downstream from potential water overflows or unmetered connections, because such measurement could not be compared with customer measurements.

4. If there is an opportunity for further development of the settlements or the extension of distribution network itself, then the manhole construction point must be upstream from respective settlement.

5. Ultrasonic flow meters can perform accurate measurements only if the is completely filled with a very important precondition for the selection of measurement location is that the pipe is filled with water.  One should also take care not to leave any possibility of creating air pockets at the measurement point.

6. Pipe where the flow meter shall be installed must be on a certain line at a certain length upstream and downstream from the measurement device in order to avoid uneven turbulence at the measurement point due to which the measurement would beThese principles for each individual case are described later in text.

Basic Data Required for Measurement with Ultrasonic Flow Meter

Regardless of the manufacturer, production year and model, the same data is entered in all flow meters:

1.Pipe material

2.Outer pipe diameter in mm

3.Wall thickness

4.Type of fluid measured

5.Pipe insulation thickness (always try to remove the pipe insulation because the measurement is more reliable and the device installation much simpler)

Since we previously identified measurement unit in which the measurement shall be expressed (in most cases m3/h or l/s) and entered the above data, by putting the device into operation, it shall give us data on the type of probe, mode to be used during the measurement (diagonal or reflex) and the distance between the probes.  One probe is always fixed while the other is installed at a certain distance from it. 


 Figure : Flow measurement with the ultrasonic flow meter – diagonal mode



Figure: Flow measurement with the ultrasonic flow meter – reflex mode

The probes at most of devices are installed on calibrated transducer pipe mounting fixture and this installation is very simple. Probes set in this way are being fixed, together with the calibrated transducer pipe mounting fixture, to the pipe with the chain or tape which are the accessories of the water meter. 

Once the probes are connected to the processor of the meter, it is necessary to check the signal strength through the pipe.

Then the flow measurement can start, following which the only remaining thing to do is to switch on and customize the logger on the device which shall record data in the memory of the device.

During the customization of the logger, it is necessary to be careful that the number of data we shall receive by the determination of the recording intervals corresponds to our needs, as well as not to overload the device memory because it can stop the operation of the logger.

For night measurement, as well as all other measurements that last less than 6 hours, measurement interval should be between 30 and 60 sec.

When the device is used during the measurement with balance method which lasts 7 day minimum, recording interval is set to the period between 5 and 30 min.

Measurement unit is determined based on the flow value.  In the event of lower flows it is better to set the measurement device at u m3/h which value index is 3,6 times higher in comparison to the measurements expressed in l/s. Measurements in l/s is more convenient with higher flows.

Measurements with the Ultrasonic Flow Meter Depending on the Pipe Material 

The most convenient pipes for the measurements with the ultrasonic flow meter are PVC pipes on which internal walls, due to being very smooth, the lime scale is least formed.  Apart from that, PVC pipes are easy to prepare for measurements, and it is sufficient only to clean them.  Slightly less convenient are PE and PEHD pipes.  Steel pipes require much longer and wider measurement preparation. 

On steel pipes, before beginning with the installation of probes on the measurement point, it is useful to hit the pipe with the hammer so as not to damage the pipe.  By doing this, the internal lining of the pipe is released from lime scale deposits which shall enable better reception of the signal.  Ductile iron pipes are even more demanding in comparison to the steel ones, while asbestos cement pipes are inconvenient for the measurements with the ultrasonic flow meter and measurements on them should never be performed with this device.  In case the such measurement really have to be performed, if the measurement can be set-up, then data obtained should not be taken for granted and on no account can we rely on them.  We can only regard is as information about the flow direction.

Preconditions to be Provided for the Measurement with the Ultrasonic Flow Meter

In order to perform accurate measurements with any ultrasonic flow meter, the following should be done: 

1.The pipe must be completely filled with water 

The ultrasonic meter operates on the principle on measurement of liquid flow velocity in the pipe.  This velocity is being multiplied by a pipe cross-section and the flow value is obtained. 

Q=A x V

If the pipe is not filled with water, then the flow displayed on the instrument shall be higher by the same value as the pipe cross-section is higher than the cross-section of the pipe filled with water and which shall remain unknown.

This is something that should be always taken care of because very often it is the case that because of making this mistake, a result which makes no sense and flows that are much higher than realistic ones are obtained.

If here is a doubt that the pipe is completely filled with water, then it is necessary to install probes perpendicular to the pipe.  In case there is no way to set up the measurement, than it is a sure sign that the pipe is not completely filled with water.

In case the measurement can be set up, then the pipe is completely filled with water and the probes are installed in accordance with the norms at “two o’clock” in reference to the closk (2/3 the height of the pipe).

Figure: Flow measurement with the ultrasonic flow meter – is the pipe full



2.There should not be too many air pockets in the pipe

 As stated in the abovementioned case, the presence of the air pockets stops or obstructs the measurement. 


Figure: Flow measurement with the ultrasonic flow meter – air pockets

If the probes are installed vertically, the possibility that the air pockets shall obstruct the measurement is much greater than in case the probes are installed on the sides of the pipe (on the upper half of the cross-section of the pipe).

3.Water flow velocity through the pipe must be above the lower sensitivity level of the


Figure : Flow measurement with the ultrasonic flow meter – velocity

Ultrasonic flow meters have a defined sensitivity level for the liquid flow velocity.  This limit depends on the type of the device and usually ranges between 0,05 and 0,03 l/s.  This limit can become a problem with oversized pipelines.  The only way to solve a problem is to construct a measurement point where a lower-profile pipe shall be installed.

4.Water flow in the pipe must be uniform turbulent, not nonuniform

If the flow through the pipe is turbulent, the measurement shall be more difficult and invalid.  Sure sign of turbulent flow in the pipe is great and fast flow fluctuations which are read on the device.  Turbulence always occurs behind pipe joints, valves, T-pieces and alike.  



Figure : Flow measurement with the ultrasonic flow meter – turbulence

In order to be sure that the flow in the pipe where the measurement shall be performed is laminated, the following criteria must be met:

  • Impact of 90° elbow on the selection of measurement point
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Figure : Schematic representation of the impact of 90ş elbow

The best position for measurements is at 5 diameters upstream (the most), or 15 diameters downstream (the most) the joint.

  • Impact of active valve on the selection of the measurement point
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The best position for measurements is at more than 10 diameters upstream or at 25 or more diameters downstream the active valve.

  • Impact of “T” junction on the selection of the measurement point
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Figure: Schematic representation of the impact of “T” junction

The best position for measurements is at more than 5 diameters upstream or at 10 or more diameters downstream the “T” piece.

  • Impact of transfer from smaller - large junction  on the selection of the measurement point

The best position for measurements is at more than 1 diameter upstream or at more than 10 diameters downstream the reduction.


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Figure: Schematic representation of the impact of samall - large junction

  • Impact of “Y” junction on the selection of the measurement point


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Figure: Schematic representation of the impact of “Y” junction


The best position for measurements is at more than 5 diameters upstream or at more than 10 diameters downstream the “Y” junction.


  • Impact of the pumping station on the selection of the measurement point

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Figure : Schematic representation of the impact of the pumping station


Different types of pumps cause different flow fluctuations, but for each it shall be enough to install the device at the distance of 15 diameters from the last pump in the series.