WO2007086049A1

WO2007086049A1 - Calibration method for turbine flow meter

Info

Publication number: WO2007086049A1
Application number: PCT/IL2007/000043
Authority: WO
Inventors: Ilan Paz; Lawrence Berman
Original assignee: Estec Flow Control Ltd
Priority date: 2006-01-24
Filing date: 2007-01-11
Publication date: 2007-08-02
Also published as: IL173321A0; WO2007086049A9

Abstract

The present invention provides a fluid flow meter that generates pulses proportional to the flow therethrough, both at high flow rates and low flow rates, the meter being at least temporarily in fluid connection with a further means for determining the actual flow rate through the flow meter, whereby the time between pulses can be calculated and a graph of time between pulses versus volume per pulse can be generated for each specific meter, enabling the creation of a table having discreet O order and first order curve regions with the characteristics of the specific meter which can then be downloaded into the specific meter when operating in any one of the specific predetermined regions and thereby enabling an accurate calculation of volume per pulse and hence flow rate for the specific meter.

Description

CALIBRATION METHOD FOR TURBINE FLOW METER

The present invention relates to an electronic fluid flow meter. More specifically the present invention relates to a self calibrating fluid flow meter that generates pulses proportional to the flow therethrough both at high and low flow rates.

As is known there are different types of flow meters, including jet meters of the single jet, multi jet and Waltman types, displacement meters of the undulating disc and rotating cup type, and electronic meters of the magnetic, doplar and ultrasound type.

The jet meters are known to have a large range, however, are not accurate at low flows. The displacement meters are very accurate, however, are prone to wear and can only be used in contexts in which the fluids are very clean. The electronic meters are very accurate, however, are affective only over a small flow range, are very expensive and involve high power consumption, and therefore cannot work for extended periods on a battery system, and therefore are used principally in plants where electric supply is available.

It is an object of the present invention to provide a fluid flow meter that generates pulses as a result of the flow therethrough, either with or without a mechanical moving part. It is further object of the present invention to provide a flow meter that generates pulses wherein the time between the pulses is directly proportional to the flow at each flow rate, i.e., the pulses per volume will change at different flow rates.

The present invention is preferably applicable to single or multi jet meters, and to volumetric meters of the various types, as will be described hereinafter.

In the meters of the present invention at least two pick-ups are used and said pick-ups can be magnetic, optical, inductive capacitive, etc. Each pick-up records the flow situation at a specific flow rate as described hereinafter.

More specifically according to the present invention, there is now provided a fluid flow meter that generates pulses proportional to the flow therethrough, both at high flow rates and low flow rates, said meter being at least temporarily in fluid connection with a further means for determining the actual flow rate through said flow meter, whereby the time between pulses can be calculated and a graph of time between pulses versus volume per pulse can be generated for each specific meter, enabling the creation of a table having discreet 0 order and first order curve regions with the characteristics of said specific meter which can then be downloaded into said specific meter when operating in any one of the specific predetermined regions and thereby enabling an accurate calculation of volume per pulse and hence flow rate for said specific meter.

In preferred embodiments of the present invention said meter is provided with a rotating element responsive to the flow of fluid and with at least two pick-ups positioned to register at least 4 pulses for each rotation of said element, such that a truth table may be created as a result of said flow, wherein said table consists of 4 sets of results representing a unit of flow through said meter as determined by a single rotation of said element, thereby providing a sampling interval, and information as to the number of pulses per interval, which increases the resolution by a factor of 4.

If these pickups are mounted at 90° from each other, then the 4 pulses will be equal.

As a result of mechanical mounting constraints, these pulses may not be identical, i.e., they may be slightly different from each other.

In such a case, each individual pulse can be used for determining volume.

An average of 4 pulses can be used for determining and presenting the flow rate. This gives a much more constant and accurate flow rate reading.

At very high flow rates, and in order to save power, the sampling rate of the microprocessor may not be capable of handling such a fast pulse rate. Under these circumstances, groups of pulses may be used for calculation purposes, e.g., groups of 4 pulses, groups of 8 pulses, etc.

Thus in preferred embodiments of the present invention, said flow meter is provided with 2 pickups positioned at 90° intervals from each other to provide 4 equal pulses per rotation of said element.

In especially preferred embodiments of the present invention, said fluid flow meter further comprises at least one further pickup to provide for redundancy.

In preferred embodiments of the present invention, said fluid flow meter is provided in combination with a supporting program adapted to input information from said meter and to apply it for generating algorhythmic curves of 0 order and first order curve regions to create said table and to download the same into a meter. Preferably the test time interval is automatically set according to the flow rate.

In some preferred embodiments of the present invention, the pulse states are averaged in order to provide an accurate and smooth flow rate.

In other preferred embodiments of the present invention, for pulse rates which are too high for accurate measurement at the preferred micro processor sampling rate in light of power considerations and constraints, a plurality of pulses are grouped and recorded as a single unit and then multiplied by the number of pulses in the group.

The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood.

With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

In the drawings:

FIG. 1 is a sectional elevational view of a prior art meter as described in WO2005/043091 in which meter the features of the present invention can be incorporated; FIG. 2 is a perspective view of a rotor of said prior art meter;

FIG. 3 is an upside down perspective view of a printed circuit board carrying two pairs of optical transmitter-receivers for reverse rotation detection for said prior art meter; Figure 4 is a graphical representation of a typical flow curve of a multi jet meter, in which pulses per liter are plotted against flow rate on a log scale. Figure 5 is a graphical representation of a the same multi jet meter, wherein volume per pulses is plotted against time between pulses on a linear scale; and Figure 6 is an enlarged graphical representation of area A from Figure 5, wherein volume per pulses of high flows are plotted against time between pulses, and are subdivided using 0 order curves. There is seen in FIG. 1 a prior art flow-through fluid consumption meter 10 of the type described and claimed in WO2005/043091. The meter is suitable for use with most transparent fluids, including fuels. The meter 10 shown is optimized for use as a water meter.

The meter 10 is of the type having a chamber 12 in which a rotatable part 14 is revolved by fluid flowing through the chamber 12. The rotatable part 14 seen is arranged to drive a first, lower end of an upper shaft 16. An upper bearing 18 revolvably supports the upper shaft 16. Above the bearing 18 and proximate to an opposite upper second end of the upper shaft 16 there is rigidly attached an opaque rotor 20 having a partially cutaway surface 22.

A preferred embodiment of the rotor of said meter is shown in FIG. 2.

The rotor 20 is free to revolve without contacting the walls of a transparent enclosure 23, and is driven, being rigidly attached to the upper shaft 16, by the fluid-driven rotatable impeller part 14. In the shown embodiment the rotatable part 14 is flexibly supported between the upper shaft 16 free to revolve in the upper bearing 18 and a lower shaft 24 free to revolve in a lower bearing 26.

The rotor 20 is positioned between an optical transmitter 28 -receiver 30 pair which detects the blocking presence of the rotor 20 and the non-blocking cut-away area 32 of the rotor surface. The optical transmitter-receiver pair 28, 30 is supported on a printed circuit board 33 disposed in a dry chamber 34 electronically connected by a flexible cable 36 to an information processing unit 38 arranged to receive and record data regarding the revolution of the rotor 20.

The optical transmitter-receiver pair 28, 30 and supporting electronic circuits operate on a current of less than 5 microamperes. Power is supplied by a lithium cell 40 configured for low current/long life application. Voltage is about 2 - 5, and expected life of the cell is 15 years, which exceeds the expected life of the meter. In the present embodiment pulsed current is applied to further reduce power consumption.

A preferred operational mode is to arrange the optical transmitter-receiver pair 28, 30 to operate at infra-red frequency.

The information processing unit 38 appears as a printed circuit board housed in the fluid consumption meter 10. The board includes a digital display 42 which can be manually read through the glass 44, and communication means, which is part of the information processing unit 38, compatible with an AMR system. The meter does 10 not contain any magnet, and so it can not be manipulated to give false low readings.

With regard to the rest of the figures, similar reference numerals have been used to identify similar parts.

Referring now to FIG. 2, there is seen a half cut-away rotor 46 for use in a flow- through fluid consumption meter of the type shown in FIG. 1.

The rotor 46 has a cup-like shape, with about one half of its wall 48 cut away at 50. The rotor is attached to the upper shaft 16.

The rotor 46 is balanced by thickening of the lower portion 52 at a location opposite the wall 48.

When in operation the rotor 46 is disposed on the inside of the transparent cover 23, as seen in FIG.1 , The light transmitter (emitter) 28 sends a horizontal beam to the receiver (detector) 30 which is disposed in a central cavity of the transparent cover 23. The wall 48 forms an opaque section which prevents light from the transmitter 28 reaching the detector 30, while the cut-away portion 50 allows the free passage of light. Determination of the number of revolutions made by the rotor 46 is easily handled by the information processing unit 38 seen in FIG. 1 on the basis of the current pulse transmitted by the detector or pick up 30.

FIG. 3 illustrates a detail of a flow-through fluid consumption meter, the detail being shown upside down for illustrative purposes.

Two sets of the transmitter-receiver pairs 28, 30 are arranged, at about 90° to each other, and are positioned on a printed circuit board 54 so that when in operation the wall 48 of the cup-like rotor 46 seen in FIG. 2 passes between the pick ups 30 and the light emitters 28. The arrangement detects whether the rotor 46 is revolving in the forward direction, or in the reverse direction as could result by a consumer tampering with the meter. The information processing unit 38 seen in FIG. 1 simply compares the time between a pulse received from pick up 3OA and the pulse received from pick up 3OB to determine direction of motion. Reverse direction rotation can be arranged to signal an alarm to an AMR system, or to trigger a release mechanism (not shown) for a red dye fluid held in a frangible container to stain components in the dry section of the meter.

For purposes of description and understanding of the invention, reference will now be had to a mechanical multi jet flow meter as a preferred embodiment of the present invention. Referring to Figures 2 and 3, there is shown a half cut-away rotor 46 mechanically linked by shaft 16 to an impeller 14 (shown in Figure 1), which impeller rotates as a result of fluid flow through the meter.

Two sets of the transmitter-pick up pairs 28, 30 are arranged, at about 90° to each other, and are positioned on a printed circuit board 54 so that when in operation the wall 48 of the cup-like rotor 46 seen in FIG. 2 passes between the pick ups 30 and the light emitters 28., although a third or more transmitter-pick up pair can be added for redundancy.

As the rotor 46 rotates, first, pick-up 1 (hereinafter referred to as PU1) (30A), and then pick-up 1 and pick-up 2 (hereinafter referred to as PU2) (30B) are obstructed. Thereafter, PU1 is not obstructed, while PU2 is obstructed, and then both PU1 and PU2 are not obstructed.

Based on the above, a truth table can be constructed for the 4 states of the pick-ups during a full rotation of the half cut-away rotor, as shown in Table 1 , hereinafter.

Table 1

As the rotor position changes from state to state, it is also possible to identify if the meter is recording a forward or backward flow based on whether the state is changing in the direction of state 1 to state 4, which is designated as forward flow, or in the direction of state 4 to state 1 , which is designated as backward flow, said changes of state being referred herein as pulses.

It is therefore possible to pick-up 4 flow pulses for each rotation of the impeller which provides for 4 times the resolution of commonly used electronic meters.

By conducting a test in order to construct a flow curve, flow through the meter at specific flow rates is measured, the time between pulses is recorded, and by utilization of an external master flow meter recording the flow rate through said meter, the specific characteristics of a specific meter can be plotted.

When testing, and thus constructing the flow curve for a meter, there is chosen a testing time interval with an arbitrary default of e.g. 4 seconds, which default is increased at the low flow rates to e.g. 30 seconds. The time interval from the start time of the first pulse to the end time of the last pulse is then measured, and in order to obtain a full pulse after said end time, one waits for the next pulse stop time. Pulses are counted in this time.

The standard manner of plotting a flow curve is that of pulse per liter or pulses per unit volume, versus flow rate wherein a logarithmic scale is usually used for plotting flow rates from low flow rates to high flow rates.

As is known, each and every meter type will have its own specific meter characteristics.

The above method of representation as shown in Figure 2, is an acceptable way for viewing the flow characteristics of the meter, however, for it to be of any use, the flow rates must always be plotted on a logarithmic scale, in order to compensate for accuracy. In this format, it is extremely cumbersome and problematic for said representation to be readily handled by a micro processor.

A preferred objective of the present invention, is to compensate for the curve characteristics generated in the above manner, and to provide for a curve correction which would render the meter more accurate at all flow rates.

According to the present invention, the electronic flow meter records the time between pulses, i.e., the changes of state as discussed above, as well as the number of pulses in the time interval being tested. As will be realized, the longer the time interval, the more pulses and the greater the accuracy.

At each specific flow rate, the flow rate is determined either by recording volume passing through the meter in a measured time interval, wherein flow rate is equal to volume over time, or by an external master flow meter.

If one were to plot the time between pulses in a meter as measured by a micro processor versus volume per pulse, determined by the number of pulses in the time period measured by the micro processor in the meter and flow rate as above, one can plot the results on a linear scale wherein the low problematic flow rates are represented in more detail than the high flow rates. The higher the flow rate, the shorter the time between pulses (TBP) and the lower the flow rate, the longer the TBP. It has now been found that this is a perfect representation for curved compensation as both scales on the graph are linear and can be easily computed by a micro processor with a spreading out of the problematic area of low flow, as shown in Figures 3 and 4 appended hereto.

All calibration calculations and building of graphs, are carried out in a supporting calibration software package.

Each meter to be calibrated communicates its information with regard to its predetermined test time and the number of pulses in the predetermined test time period, at the request of the calibration software.

Before testing, the calibration software informs the meter of the predetermined test time. If this is not done, then the meter uses a default time period of e.g., 4 seconds. The flow rate will be proportional to the volume registered by the meter.

This default time may be set automatically by the microprocessor of the meter. Once a curve TBP (time between pulses) versus volume per pulse is in the calibration software, then the curve maybe cut up using a predetermined algorithm. In specific regions, 0 order slope and first order slope curves can be used. Typically 0 order curves will be used where changes are small in the meter curve characteristics, i.e., relating to high flows, and first order curves will be used where changes are great, typically at low flows. Any number of steps or regions may be used, and in any order, however, it has been found that about 15 0 order curves and about 3 one order curves are sufficient.

As will be realized, calibration may be done in both the forward and the reverse directions.

A text table of volume per pulse and TBP (time between pulses) for 0 order and, additional slope for first order is downloaded into the meter micro processor.

As the meter rotates, the time between pulses is measured. For each pulse a volume is incremented to the volume according to the above table..

As is known, flow meters are rated by their "Qmax" and their "Qnom", wherein, the Qmax, or Q maximum, is the maximum flow rate that will pass through the meter, and "Qnom", or Q nominal, is equal to Qmax divided by 2, and is a typical representation of a standard flow meter and its characteristics as are shown in Figure 2 appended hereto.

Referring to Figure 3, there is seen a graphical representation of volume per pulse as plotted against time between pulses (TBP) in a linear graph and in Figure 4, there is seen an enlargement of block A of Figure 3, wherein the curve generated is cut up using an algorhythm using 15 zero order curves to identify the characteristic steps at high flows and 3 first order curves are used to identify the characteristic steps at low flows as seen in Figure 3.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

WHAT IS CLAIMED IS:

1. A fluid flow meter that generates pulses proportional to the flow therethrough, both at high flow rates and low flow rates, said meter being at least temporarily in fluid connection with a further means for determining the actual flow rate through said flow meter, whereby the time between pulses can be calculated and a graph of time between pulses versus volume per pulse can be generated for each specific meter, enabling the creation of a table having discreet 0 order and first order curve regions with the characteristics of said specific meter which can then be downloaded into said specific meter when operating in any one of the specific predetermined regions and thereby enabling an accurate calculation of volume per pulse and hence flow rate for said specific meter.

2. A fluid flow meter according to claim 1 , wherein said meter is provided with a rotating element responsive to the flow of fluid and with at least two pick-ups positioned to register at least 4 pulses for each rotation of said element, such that a truth table may be created as a result of said flow, wherein said table consists of 4 sets of results representing a unit of flow through said meter as determined by a single rotation of said element.

3. A fluid flow meter according to claim 2, provided with 2 pickups positioned at 90° intervals from each other to provide 4 equal pulses per rotation of said element.

4. A fluid flow meter according to claim 2, comprising at least one further pickup to provide for redundancy.

5. A fluid flow meter according to claim 1 , in combination with a supporting program adapted to input information from said meter and to apply it for generating algorhythmic curves of 0 order and first order curve regions to create said table and to download the same into a meter.

6. A fluid flow meter according to claim 1 , wherein the test time interval is automatically set according to the flow rate.

7. A fluid flow meter according to claim 2, wherein the pulse states are averaged in order to provide an accurate and smooth flow rate.

8. A fluid flow meter according to claim 2, wherein, for pulse rates which are too high for accurate measurement at the preferred micro processor sampling rate in light of power considerations and constraints, a plurality of pulses are grouped and recorded as a single unit and then multiplied by the number of pulses in the group.