WO2019063535A1

WO2019063535A1 - Device for measuring velocity, method and use thereof

Info

Publication number: WO2019063535A1
Application number: PCT/EP2018/075942
Authority: WO
Inventors: Anders WEDELL
Original assignee: Mark & Wedell A/S
Priority date: 2017-09-26
Filing date: 2018-09-25
Publication date: 2019-04-04
Also published as: DK179702B1; DK201770727A8; DK201770727A1

Abstract

A device (1) for measuring velocity inside a flowing channel (20). The device (1) is configured to be inserted into the flowing channel (20) through an opening (21) therein. The device (1) comprises a shaft (9) having a proximal end (11) and a distal end (10). A velocity measuring probe (3) located at the distal end (10) of the shaft (9), and at least a first and a second reference points (13,12). The first reference point (13) is moveable with respect to the shaft (9) and the second reference point (12) is at a predetermined location with respect to the proximal end (11) of the shaft (9) thereby providing a variable distance between the first and the second reference point (13,12). The device (1) comprises an electronic range sensor (16) configured for determining the variable distance.

Description

Device for measuring velocity, method and use thereof Background of the invention

The present invention relates to a device for measuring flow velocity in a flowing channel with particulate, and also method and use of such a device.

Such instruments are used for measuring in flowing channels, such as pipe or duct systems that transport dusts, such as for example pulverized coal, cement, lime, food stuff or similar dusts. Such pipe or duct systems is often comprised of many flowing channels transporting dusts from a storage or mill facility to a receiving facility. Coal dust may for example be transported via flowing channels from a storing facility to a burner, being injected into the burner at different entry points. It is important that the optimal volume of coal dust is injected into the burner at the different entry points to obtain an optimal combustion. This is controlled by regulating the pressure inside the channel. However, several factors affect the relation between pressure and flow volume of dust and adjusting the pressure is therefore nontrivial. Such factors may be varying particle size or the different channel layout resulting in different lengths and bends in each individual channel.

Measurement of flow properties in a flow comprising both a gas and dust is difficult since the flow often is far from laminar. The flow is likely to segregate and swirl inside the channel. The dust flows in swirling jets or "ropes" inside of the channel which results in high and low concentration areas of dust inside of the channel and thereby also a varying radial pressure gradient.

The degree of segregation and swirling is the highest after a change in flow, such as a change in flow direction.

In order to retrieve a representative sample from such a flow and obtain information about the flow volume of dust, it is preferred to have the measurement point at a straight part of the channel located at a distance downstream of a bend corresponding to 5 times the diameter of the channel. Depending on the sampling method this may for example require information about the pressures (such as pipe static pressure) and temperature in order to estimate the air velocity (so called dirty air velocity) and finally determine the volume flow of dust. The most accurate measurements are made by performing the measurements at operation conditions.

Several different methods can be used to measure the dust volumes in a flowing channel. A preferred method is an isokinetic sampling method where particles are sampled with the same velocity as the particles are flowing in the channel. In such a method an open tube is inserted into a flowing channel. The tube is arranged such that the flowing particles can enter the tube. The tube is provided with a suction which corresponds to the flowing velocity in the channel and the dust will therefore flow natural into the opening and give a representative sample. If a lower suction is used in the sampler this corresponds to a lower velocity and would give a smaller sample than otherwise. A higher suction in the sampler would correspond to a higher velocity and give a higher sample since it would suck out additional dust. Reliable data from such a measurement therefore requires reliable knowledge of the velocities in the channel.

According to standardized methods for sampling dusts, samples taken from a channel must represent the entire cross section of the flow channel. Similarly flow velocities representing the entire cross section of the channel are required to perform such a test.

As per ISO 9931 standard, multiple measurement points along the diameter are required. These measurements must be made with the per standard required precision and at the number of measurement points. The positions of the measurement points are calculated based on the diameter of the flowing channel. A requirement for performing this sampling is therefore to get an ac- curate velocity profile of the channel.

Different types of such instruments, often referred to as a Dirty Air Probe (DAP), are known in the prior art. It typically comprises a probe mounted on a shaft configured to enter through an opening of a channel. A typical probe comprises a reflection disc. The disc should during a measurement be held with its radial axis perpendicular to the flow direction. Two small pressure sensors are located on each side of the reflection disc and performs a pressure measurement. The pressure measured on the up-stream side of the disc correspond to the total pressure in the channel and the pressure measured on the downstream side of the reflection disc correspond to the static pressure. The velocity can be found using the simplified Bernoulli equation which relates ve- locity to the difference between total pressure and static pressure and mass density of the fluid. For e.g. air, the air density at actual conditions can be found by correcting the mass density of atmospheric air to the conditions (temperature) in the flowing channel. Thus, the velocity can be determined based on temperature and differential pressure, i.e. the difference between total and static pressure.

In the opposite end of the probe, the shaft may comprise a handle. The device also comprises a manometer wherefrom the probe measurements can be read. Since the instrument is used while the channel is flowing, the insertion of the probe is typically made through a gate valve or "dustless connector", which ensures that the dust and gas is kept inside of the channel while the measurements are made. The instrument may comprise a lock arrangement which fits into the gate valve and ensures a tight seal between the valve and the instrument. The lock arrangement is movably attached on to the shaft, allowing the shaft, and thereby also the probe, to slide back and forth while the device is locked into the gate valve. The length of the shaft should be minimum as long as the outer diameter of the channel in which the measurement is performed.

In order to measure velocity at the determined positions inside the pipe, the prior art instruments are typically fitted with a ruler or similar means for measuring distance. The ruler is typically in one end fastened to the lock arrangement and is movably connected to the handle such that a movement of the handle will show as a displacement on the ruler. The ruler will typically have to be as long as the shaft in order to measure a full displacement of the probe. A device which can be used to measure inside a channel with a diameter of 60 cm will be at least 120 cm with a mounted ruler. The length makes the device unhandy and unsuitable for transport. During transport the ruler will therefore be unattached from the device. Prior to perfornning a measurement, the sampling points will have to be calculated. Firstly, the operator will have to find the inner diameter of the channel which can be calculated based on the outer diameter or looked up in the specifications of the channel. Once the internal diameter is determined the sampling points can be determined by calculation based on formulas e.g. found in the ISO standard.

Once the sampling points are determined, the probe is fully entered (or traversed) into the channel such that the probe touches the channel wall on the remote side of the channel. The dustless connector is then fastened to the lock arrangement on the device. The ruler may now be calibrated by moving a reference point near the handle to a starting value on the ruler. The probe is now moved to each of the sampling points by moving the reference point to the correct value on the ruler. For a channel with a diameter of 60 cm, the first three measurement points may e.g. be 1 ,9 cm, 6,3 cm and 1 1 ,6 cm. When the refer- ence point near the handle is positioned at the calculated measurement point the movement of the probe is stopped.

While keeping the probe precisely at the measurement point, the probe may now be rotated by turning the shaft, so that the reflection disc is oriented correctly. The measured differential pressure may now be read from the manometer and should be noted down.

A particular problem with this prior art method is that it is slow and leaves room for human error since both the value on the ruler and measurements from the probe has to be read simultaneous and noted down while keeping the probe at an angle sufficient to provide correct measurements.

A further typical complication occurs when a measurement point is located at a vertical section of a channel system. Since a measurement point should be located at a distance which is least 5 times the diameter from the nearest upstream bend, the operation of performing a measurement can occur at an elevated position. E.g. if the diameter of the channel is 60 cm the meas- urement point should be located at least 3 meters downstream from the nearest bend.

Unless the building is designed with catwalks, the operator may risk performing a measurement from a ladder 3 meters above the ground. The operator will in such a case have to climb up the ladder with the at least 120 cm long device, insert the probe into the opening of the measurement point, fasten the dustless connector to the lock arrangement, fully traverse the probe to the remote wall of the channel and now calibrate the ruler.

While balancing on the ladder, the operator will, most like using only one hand, have to look up the calculated measurement point and move the probe to a first position. The operator will then have to rotate the shaft in order to orient the reflecting disc correctly, and while keeping the probe at the desired position, note down the measurement from the manometer, before moving on to the next measurement point.

This is an additional problem when the channel diameter is shorter than the ruler. In such a situation it will not be possible to traverse the probe the its fully extended length and the starting point which is read on the ruler will not correspond to zero. Each calculated probe position will therefore have to be shifted according to this distance.

Summary of the invention

It is an object of the present invention to mitigate the above mentioned problems and provide an improved device and method for measuring inside a flowing channel.

According to a first aspect of the invention this object is achieved by a device for measuring velocity inside a flowing channel, said device being configured to be inserted into said flowing channel through an opening therein; the device comprising a shaft having a proximal end and a distal end, a velocity measuring probe located at the distal end of the shaft, and at least a first and a second reference points, wherein the first reference point is moveable with respect to the shaft and the second reference point is at a predetermined location, located with respect to the proximal end of the shaft thereby providing a variable distance between the first and the second reference point, said variable distance between the first and second reference point serving to identify the position of the velocity measuring probe in the flowing channel; wherein the device comprises a range sensor configured for determining the variable distance value between the at least first and the second reference point.

The range sensor should be understood as an electronic device which is able to determine a variable distance.

The range sensor may determine a variable distance in a contactless manner. The range sensor could be a laser range sensor which utilize laser to obtain such a measurement. Alternatively, the range sensor could use ultra sound to obtain such a measurement.

The range sensor could also be of another type of electric range sensor able to determine a variable distance.

The range sensor makes it possible to determine the distance between the at least first and second reference points and thereby also the probe location in the flowing channel, much faster and provides a more reliable positioning of the probe. Furthermore, the length of the measuring device is reduced con- siderable as compared to the prior art devices since the second reference point is at a predetermined location located with respect to the proximal end of the shaft rather than on a ruler.

The meaning of the wording "located" is to be interpreted as "located in the vicinity of. For instance, the predetermined location of the second refer- ence point may be at an offset from the proximal end of the shaft. The second reference point may therefore be located on a portion located in the proximal end of the device. This position ensures that the reference point is located outside of the flowing channel when performing a measurement. As an example the reference point may be displaced towards a direction perpendicular to the length of the shaft. E.g. the second reference point is located on a surface, said surface contacting the proximal end of the shaft.

The wording "measuring velocity" means in this context a measurement of any physical parameter which can be used to determine the velocity. The "velocity measuring probe" may therefore perform a measurement of any desired parameter which can be used to determine the flow velocity. This could for instance be rotations in a vane anemometer, resistance of a hot-wire anemometer or pressures measured by a tube anemometer. The latter might be a pitot-static tube.

According to a preferred embodiment the device for measuring velocity further includes a data processing means adapted to receive measurement data from the probe.

The data processing means is connected to the probe by communication means such as by wire or by a wireless connection.

The data processing means improves the usage of the device since the measurement data from the probe automatically can be send to the data processing means without any action from the operator. Furthermore, since the data processing means is adapted to receive the measurement data from the probe the operator do not have to read the instrument and several measurements can therefore be made faster.

According to a further embodiment the data processing means is adapted to calculate probe positions in said flowing channel, based on a known cross sectional dimension value, and performing measurements at predetermined probe positions.

The data processing means is adapted to communicate with the range sensor and is adapted to calculate probe positions in the flowing channel based on a known cross sectional dimension value. Thus, the data processing means is adapted to communicate with both the range sensor and the probe.

The known cross sectional dimension value is the cross sectional dimension value of the flowing channel in which the measurements are to be performed. For a cylindrical flowing channel, the cross sectional dimension value corresponds to the diameter. Based on the cross sectional dimension value of the flowing channel, the data processing means calculates the positions of the required measurement points. The data processing means is therefore able to determine the probe position inside the flowing channel and can register when the probe is at a measurement point, while it simultaneously obtains velocity measurements from the probe. During a traverse of a flowing channel the data processing means will continuously receive probe locations and probe measurements and is able to determine which probe measurements were performed at the required measurement points. By traversing the probe across the cross sectional dimension and thereby in succession, positioning the probe at the measurement points it allows the data processing means to gather measurement data from each of the measurement points. The traverse can, as a consequence, be one continuous movement, which provides a much faster reading compared to the prior art. The cross sectional dimension value can be manually entered into the data processing unit whereby the measurement points are calculated. In another embodiment the known cross sectional dimension value of the flowing channel is found by traversing the velocity measuring probe across the flowing channel. By traversing the probe across the cross section of the flowing channel to obtain the cross sectional dimension value the data processing device will always use the correct value. This hinders that an erroneous value inadvertently is used to calculate the measurement points.

In a particular embodiment the device for measuring velocity com- prises a data storing unit. The data storing unit is adapted to receive and store data from the data processing unit. The data which is measured by the probe and the range sensor and processed by the data processing unit can be stored. The data storing unit may be an internal data storing unit or may be a removably connected data storing device such as a usb-device or a memory card. This allows the operator to perform measurements and store data without handling any of data.

In another embodiment the device for measuring velocity comprises means for transferring data to a remote recipient.

The remote recipient may be a data processing device adapted for receiving data. The remote recipient may also be a device for collecting a dust sample, such as for example an isokinetic sampler which comprises a data processing unit adapted to receive data. The data processing unit in an isokinetic sampler uses the measured velocities to regulate the pressures in the sampler while performing the sampling. The transfer of measurement data di- rectly from the velocity measuring device to a dust sampling device prevents any inadvertently typing mistakes.

In a particular embodiment the velocity measuring probe measures differential pressure. The probe may e.g. comprise a reflection disc wherein a pressure measurement is made on each side of the reflection disc. Based on the two pressure measurements the differential pressure can be obtained and used by the data processing means to calculate the velocity. By having the data processing means calculate velocity rather than displaying the differential pressure, the measurement is made easier for the operator, since the actual measurement does not have to be calculated manually. Thus, the data processing means determines the velocity based on pressure measurements made by the probe.

For instance, the probe may be a piezoelectric sensor or the like, which can measure pressures and or differential pressure which can be used to calculate the velocity.

The velocity may be calculated based on the simplified Bernoulli equation, which relates the velocity with the differential pressure between the total pressure and static pressure and the mass density of the fluid. The mass density of the fluid medium in the flowing channel, e.g. the mass density of air, can be found at the actual conditions by having information about the temperature inside the flowing channel. If the temperatures are known, the velocity can be determined by measuring the static and total pressure in the flowing channel. In another embodiment the probe may also comprise means for measuring other parameters such as temperature, pH or concentrations. The device could in this manor retrieve more information from the flowing channel during one measurement which could save time for the operator. As an example the probe may comprise means for measuring differential pressure and means for meas- uring temperature.

In yet another embodiment the device for measuring velocity comprises a thermometer. The thermometer should have its measuring portion at the probe such that it is near the means for measuring velocity. By measuring temperature inside the flowing channel, near the pressure measuring probe it is possible to calculate and accurate mass density of the fluid and thereby determine a more accurate velocity. The thermometer is preferably adapted to communicate with the data processing means which may be adapted to perform the calculation.

In yet another embodiment the device for measuring velocity comprises a manometer. The manometer could for instance be located near the proximal end of the shaft or at a portion of the device which will be on the external side of the flowing channel during a measurement.

In another embodiment of the invention, the second reference point is located on an arrangement configured to seal the opening in the flowing channel. By sealing the opening when the probe measures velocity, more accurate measurements are obtained because any disturbances caused by an opening in the channel wall is prevented.

According to another aspect, the invention relates to the use of a device for measuring velocity according to the first aspect of the invention.

According to yet another aspect, the invention relates to a method of measuring velocity at a number of predetermined positions in a flowing channel using a device according to a first aspect of the invention, wherein velocity measurements are obtained at at least one predetermined position during the traverse of a probe across a cross sectional dimension of a flowing channel.

The traverse and measurement of velocity at a number of predeter- mined positions can be made in a continuous movement. By continuous is meant a movement without stopping the probe. The traverse may also be made with several stops, but for the fastest measurement a single movement is preferred. If measurement data from e.g. one of the measurement points are missing after the traverse, the data processing means may alert the user by means of a message on a display or a sound. The missing data may then be obtained by performing a partial traverse in the area around the measurement point with the missing data.

Brief description of the drawings

This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing a particular non-limiting exemplary embodiment of the invention. In the drawings: Figure 1 illustrates an embodiment according to the invention of the device for measuring velocity from a perspective view,

Figure 2 shows a schematic drawing of the velocity measuring probe according to the invention,

Figure 3 illustrates an embodiment according to the invention of the device for measuring velocity, shown from a side view, and

Figure 4 illustrates two embodiments according to the invention of the device for measuring velocity, where the device is inserted into an opening of a flowing channel. The figure shows one device having the probe at a position near the remote channel wall and one device having the probe at an initial position shown, both shown from a side view.

Detailed Description

Figure 1 shows one embodiment of a device for measuring velocity according to one embodiment of the invention.

The illustrated device for measuring velocity 1 comprise a probe 3 for measuring flow velocity.

Turning to figure 2 which shows a schematic drawing of a probe 3 for measuring flow velocity according to one embodiment of the invention. The probe 3 comprises a measuring object in the form of a reflecting disc (RD) 4 having an upstream side 5 and a downstream side 6. The RD 4 is arranged between two tubes 7 such that the radial plane of the reflecting disc is parallel to the tubes 7 and that one tube 7 is connected to the upstream side 5 and the other tube 7 connected to the downstream side 6 of the RD 4. This connection (not shown) is typically displaced sideways from the centre of the RD 4 and the tubes 7 such that the centre of the RD 4 can be exposed to flow.

In normal use, when the probe 3 measures inside a flowing channel, the RD 4 is oriented such that the radial axis of the RD 4 is sufficiently parallel to the cross sectional dimension plane of the channel in a manner such that the downstream side 6 of the RD 4 is oriented downstream of the flowing channel 20. The pressure near the upstream side 5 of the RD 4 corresponds to the stagnation (total pressure) and the pressure near the downstream side 6 of the RD 4 corresponds to static pressure.

The two tubes 7 are provided with pressure measurement ports 8 near the surfaces of the RD. The tubes 7 runs from the RD 4 inside the guiding tube 9 to the data processing means located in the operating handle 12.

The probe 3 may also comprise means for measuring gas temperature

15.

Now returning to figure 1 , it can be seen that the device 1 comprises a guiding tube 9 having a distal end 10 and a proximal end 1 1 . The probe 3 is attached at a distal end 10 of the guiding tube 9, which thereby enables an operator to manoeuvre the probe 3 inside a flowing channel.

The proximal end 1 1 of the guiding tube 9 has a reference point in the form of an operating handle 12 to be held in one hand by an operator. The operating handle 12 may be shaped in a manner ergonomically suitable for operator, in particular but not exclusively for the hand of the operator, as arms and joints may also play a role in ergonomics. This is particular important when measurements are performed at awkward positions, such as elevated positions on a ladder, where the operator is forced to hold on to the ladder with one hand, and only has his one remaining hand available for operating the device 1 . Accordingly, the operating handle 12 may have different shapes which facilitate proper arrangement of the RD 4 with respect to flow direction. In the particular embodiment this is achieved by a distribution of weight towards the bottom of the operating handle 12 such that the operating handle 12 is oriented by aid of gravity.

In another embodiment the orientation of the RD 4 may be aided by means of a bubble or similar inclination indicator means arranged near the operating handle 12 in order to visually orient the operating handle 12.

Turning now to figure 4 which shows an embodiment of the invention mounted onto a flowing channel 20.

The probe 3 is inserted into the flowing channel 20 through an opening 21 therein. To prevent any leaking of dust laden air from the channel 20 while inserting, mounting and/or using the device 1 , a second reference point, in the form of a bushing 13, enclose the guiding tube 9 and provide a seal between the opening 21 in the flowing channel 20 and the surroundings.

The bushing 13 may e.g. be made of brass. The guiding tube 9 is axi- ally displaceable in the bushing 13, meaning that the bushing 13 is movable along the axis of the guiding tube 9 between the distal end 10 and proximal end 1 1 of the guiding tube 9. This design enables a moveable probe 3 inside of the channel 20, by means of the operating handle 12, while the bushing 13 provides a gas tight seal. A lock arrangement 14, adapted to releasably lock onto an interface on the opening 21 of the flowing channel 20, is rotary connected to the bushing 13 allowing the bushing 13 to be easily fastened/released from the opening 21 of the flowing channel 20.

Turning now to figure 3 showing a device according to one embodiment of the invention from a side view.

In order to locate the position of the probe 3 inside the flowing channel 20, the device 1 comprises an electronic range sensor 16. Dust laden air can easily damage exposed electronic equipment and it is therefore preferred to mount limited electronic equipment/sensors on portions of the device 1 which enters the inside of the flowing channel 20. An electronic range sensor 16 is therefore adapted into the operating handle 12 to measure a variable distance between the operating handle 12 and the proximal side 17 of the bushing 13. The variable distance is illustrated as a visual light laser beam 19, but the beam may not necessarily be visual or visible during use.

This variable distance can be subtracted from the known total length of the guiding tube 9, to calculate the length of guiding tube 9 axially displaced on the distal side 18 of the bushing 13. Alternatively, the electronic range sen- sor 16 may be located in the bushing 13 and measure the distance from the bushing 13 to the operating handle 12.

This calculation is made by a data processing means (not shown) which may be located inside the operating handle and which is adapted to receive data from the electronic range sensor 16.

The data processing means is further adapted to receive data from the probe 3.

When the data processing means is turned on it continuously receives data from both the electronic range sensor 16 and the probe 3. Based on a known cross sectional dimension value of the flowing channel 20 and the measured variable distance, the data processing means calculates the position of probe 3 inside of the flowing channel 20. This position is found continuously as the variable distance is changed.

The device 1 further comprises a battery (not shown) which also may be located in the operating handle 12. The device 1 further comprises a data storing unit (not shown) which also may be located in the operating handle 12. The device 1 further comprises a data transmitter (not shown) which also may be located in the operating handle 12.

The operating handle 12 further comprise a display 30 viewable to the operator. The operating handle has three operating members 31 in the form of push-bottoms which may be individually depressed by the operator, e.g. by the index, middle and ring finger. This allow single handed use of the device 1 .

Turning now back to figure 4 showing an embodiment of the device wherein the bushing 13 is connected onto an opening 21 in the flowing channel 20, wherein the opening 21 comprises a so called dust-less connection 22, which prevents dust laden air at an elevated pressure to enter the surroundings.

In the particular illustrative drawing the flowing channel 20 is a cylindrical channel. Thus, the cross sectional dimension value corresponds to the diameter.

When the bushing 13 is mounted onto the dust-less connection 22 the probe 3 can be manoeuvred inside the flowing channel 20. For illustrative pur- poses figure 4 shows two mounted velocity measuring devices (50,51 ), each in a different position. The device 50 is displaced such that the probe 3 is near the remote inner wall 24 of the flowing channel 20. The probe 3 is oriented such that the downstream side 6 of the probe 3 is oriented towards the flow direction F. When the radial axis of the RD 4 is sufficiently parallel to the diameter plane and the probe 3 is positioned at a determined measurement point, the data processing means stores the velocity measurement. The probe 3 is then traversed along the diameter of the flowing channel 20 by increasing the variable distance between the bushing 13 and the operating handle 12.

The device 51 is illustrated in a position with its maximum variable distance. The probe 3 is in this case in a neutral position located in the opening 21 of the flowing channel 20.

By varying the variable distance, the probe 3 can be traversed over the entire diameter of the flowing channel 20. A traverse (or full traverse) is to be understood as movement of the probe 3 from the remote inner wall 24 of the flowing channel 20 to the neutral position in the opening 21 , i.e. a withdrawal, or a movement of the probe 3 from the opening 21 to the remote inner wall 24, i.e. an insertion. In a typical measurement, a number of measurements are desired, all at different positions along the cross sectional dimension of the flowing channel 20. In a full traverse, the probe 3 will be positioned at all the measurement points subsequently and the data processing unit will perform the measurement at all positions. Thus, a number of measurements can be obtained by a single movement of the device 1 , i.e. the above mentioned withdrawal or insertion.

In a method of using the invention according to any embodiment shown, the probe 3 may be entered into through the opening 21 of the flowing channel 20. The probe 3 is then positioned in the neutral position, by maximiz- ing the variable distance. By traversing the probe 3 from this initial position, towards the remote inner wall 24 of the flowing channel 20, and thus minimize the variable distance as much as possible, i.e. the above mentioned insertion, the data processing means is able to obtain the diameter value of the flowing channel 20. Based on this diameter value the data processing unit is able to determine the positions of the number of measurement points required for a complete measurement. Now, by performing the above mentioned withdrawal, and thus maximizing the variable distance as much as possible, the data processing means is able to obtain measurements from all of the measurement points.

Claims

P A T E N T C L A I M S

1 . A device for measuring velocity inside a flowing channel, said device being configured to be inserted into said flowing channel through an opening therein; the device comprising a shaft having a proximal end and a distal end, a velocity measuring probe located at the distal end of the shaft, and at least a first and a second reference points, wherein the first reference point is moveable with respect to the shaft and the second reference point is at a predetermined location with respect to the proximal end of the shaft thereby providing a variable distance between the first and the second reference point, said var- iable distance between the first and second reference point serving to identify the position of the velocity measuring probe in the flowing channel; wherein said device comprises an electronic range sensor configured for determining the variable distance value between the at least first and the second reference points.

2. The device for measuring velocity according to claim 1 , wherein the device comprises a data processing means adapted to receive measurement data from said probe.

3. The device for measuring velocity according to any preceding claim, wherein the data processing means is adapted to calculate probe positions in said flowing channel based on a known cross sectional dimension value, and performing measurements at predetermined probe positions.

4. The device for measuring velocity according to claim 3, wherein the known cross sectional dimension value is found by traversing the velocity measuring probe across the flowing channel.

5. The device for measuring velocity according to any preceding claim, wherein the device comprises a data storing unit.

6. The device for measuring velocity according to any preceding claim, wherein the device comprises means for transferring data to a remote recipient.

7. The device for measuring velocity according to any preceding claim, wherein the velocity measuring probe is adapted to measure static and total pressure in the flowing channel.

8. The device for measuring velocity according to any preceding claim, wherein the first reference point is located on an arrangement configured to seal the opening in the flowing channel.

9. Use of a device for measuring velocity according to any preceding claim.

10. Method of measuring velocity at a number of predetermined positions in a flowing channel using a device according to any preceding claim, wherein velocity measurements are obtained at at least one predetermined position during the traverse of a probe of the device across a cross sectional dimension of a flowing channel.