Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Reexamination Certificate
1999-04-19
2002-02-12
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
Reexamination Certificate
active
06345539
ABSTRACT:
This invention relates to improvements in methods and apparatus for measuring the flow of fluid in a duct. In particular, although not exclusively, it relates to insertion monitoring, in which a flow measurement probe is inserted through an opening in a wall of a duct, such as a pipe.
It is becoming increasingly common place to install fixed flow rate monitoring equipment into a duct network. An example is the provision of water meters or gas meters in the domestic utility companies pipe networks. By providing a separate meter for each household, the flow of fluid and hence volume of fluid used over time by each household can be calculated.
Because fixed meters can by their very nature not be readily removed without considerable difficulty, it has been found that the only reliable way to test the integrity and calibration of the measuring devices in the meter is to take independent on-line measurements of flow rate. These measurements can then be compared with the readings from the fixed meters. Typically, the on-line measurements are obtained by using data from insertion flow measurement devices which are inserted through an opening in the wall of the duct. In some applications, the insertion flow measuring devices are removed following testing. However, it is also possible to leave the device in the duct for a longer period, say 12 or 24 hours, or perhaps permanently.
At present, the use of the insertion monitoring techniques that exist in the state of the art prior to the present invention is restricted by financial and practical problems. In one known insertion metering device, a probe is inserted into the duct through a hole or valve opening in the duct wall. The probe comprises a rod which carries a turbine or electromagnetic sensing element on its tip. The sensing element can take a point measurement indicative of the flow in a part of the pipe at a point in time. However, because the flow in the pipe is unknown, (varying both in profile across the cross-section of the pipe and with time) several measurements must be taken at different points in the cross-section of the duct and at different times. An average can then be built up which would approximate the average flow rate. Its accuracy is limited by the difficulty in aligning the sensing element correctly along the axis of the duct.
In order to obtain reasonably accurate results, the prior art insertion technique requires that measurements are taken at several positions across at least one diameter of the pipe. However, it has been found that in practice where flow profiles are distorted that it is necessary to measure across more than one diameter (i.e. two orthogonal diameters) to provide sufficiently accurate results which can be used for calibration. This introduces severe problems when the duct system is installed underground, as it requires that a large chamber must be excavated around the pipe in order to allow access for separate circumferentially spaced holes in the pipe to be made to allow the orthogonal measurements to be made. To make the chambers can be both expensive and time consuming.
A further problem with the prior art technique is that the surface area of the rod which supports the sensing element forms a variable blockage in the duct as the element is moved across the diameter. This blockage affects the results by altering the flow profile in the duct and increases turbulence. Furthermore, the process of taking the many measurements required is subject to variability due to the often difficult operating conditions in which the measurements must be made. Often, the insertion probe operator may be working in a water filled, muddy pit which makes it difficult to obtain the various readings with any certain degree of accuracy. Different operators can get different results. It is thus desirable to de-skill the measurement process.
According to a first aspect of the invention we provide an ultrasonic insertion flow meter having a probe adapted to be inserted into a duct, said ultrasonic probe having ultrasound transducers and being adapted to perform at a single site of introduction into the duct a first ultrasonic path interrogation having a component of travel of ultrasound in a first direction that is, in use, an axial direction relative to the region of the duct where the device is inserted, and also adapted to perform a second ultrasound path interrogation having a component of travel of ultrasound in a second axial direction opposite to said first axial direction, the arrangement being such that a comparison of the signal associated with ultrasound travel in one axial direction with that of the signal associated with ultrasound travel in the opposite axial direction enables the flow rate of fluid in said duct to be estimated.
Time of flight measurements of ultrasound are effected by the flow rate and the insertion meter uses a transit time ultrasonic measurement to evaluate the flow rate.
The meter has an ultrasound emitter and an ultrasound detector.
These may be different transducers, but we prefer to use the same transducer to emit and detect. It may be possible to use appropriate reflectors spaced in use axially (relative to the duct) of a combined emitter/receiver transducer.
There may be a first emitter and receiver pair spaced apart by spacing means. There may be a second emitter and receiver pair, which may be spaced apart by the same spacing means.
Preferably the probe is adapted to measure the transit time difference of an ultrasonic pulse in the forward and reverse direction of a first interrogation path and also the transit time difference in the forward and reverse directions of a second, different, interrogation path. The average of the transit time difference in forward and reverse directions of ultrasound travel along the different interrogation paths gives a representation of the flow rate of fluid in the duct. The difference between the forward and reverse transit times of the different interrogation paths may be indicative of the swirl of fluid in the duct.
Because the ultrasound path has at least two path environments and because the ultrasound does travel through the fluid in the pipe axially (at last with an axial component) rather than a single point measurement of flow being obtained as in the prior art, the fluid flow at man different points on the ultrasound path effects the signal that i s measured. This provides a degree of in-built averaging or integration which eliminates the need to obtain many measurements at different points in the cross-section of the duct. This in turn means that the measurement process is quicker and requires less skill.
A first pair of ultrasonic transducers may be provided on one transducer mounting and may be spaced from a second pair of ultrasonic transducers provided on a second transducer mounting. In this case, the first and second pairs of transducers may communicate along two different geometric paths. The first pair of transducers may comprise the emitter of one emitter/receiver pair and the receiver of another emitter/receiver pair. The second pair of transducers may comprise the receiver of said one emitter/receiver pair and the transmitter of said emitter/receiver pair.
Preferably, the insertion meter is adapted to use the reflection of ultrasound off the sidewalls of the duct to create the first ultrasonic path interrogation and/or the second ultrasonic path interrogation. The ultrasonic paths may be beams of ultrasound. There may be more than one reflection off the duct walls as the ultrasound travels from its emitter to its receiver.
The insertion flow meter probe is adapted to take the first and second ultrasonic path interrogations whilst it is stationary.
The first emitter/receiver pair is preferably adapted to be spaced axially of the duct in use, preferably in a direction parallel to the central longitudinal axis of the duct. Similarly, the second emitter/receiver pair is preferably adapted to be spaced axially of the duct in use, preferably in a direction that is parallel to the axis of the duct.
Preferably the or each emi
Rawes William Leslie Hodges
Sanderson Michael Langley
Baker & Botts L.L.P.
Cranfield University
Fuller Benjamin R.
Thompson Jewel V.
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