Flow meter with a metering device and a control unit

Abstract

A flow meter with a metering device for intaking and metering a defined volume of a fluid, and with a control unit for controlling the fluid intake of the metering device for determining a flow rate of the fluid.

Description

BRIEF DESCRIPTION OF DRAWINGS

Other objects and many of the attendant advantages of embodiments of the present invention will be readily appreciated and become better understood by reference to the following more detailed description of embodiments in connection with the accompanied drawing(s). Features that are substantially or functionally equal or similar will be referred to by the same reference sign(s).

FIG. 1 shows a schematic view of a closed-loop control system with a flow meter,

FIG. 2 shows a schematic view of a fluidic system coupled to a flow meter with a closed-loop control system,

FIG. 3 shows a schematic view of the closed-loop control system of the flow meter of FIG. 2,

FIG. 4 shows a graph of a gradient profile starting with water and ending with acetonitrile,

FIG. 5 shows a graph of the system pressure of a fluidic system supplied with the gradient profile of FIG. 4 by a high-pressure fluid delivery system, and

FIG. 6 shows a graph of a flow accuracy in percent of said fluidic system measured by a flow meter.

FIGS. 7 and 8 show embodiments of the metering device comprising a volume displacement device 700.

FIG. 9 shows a gear pump 900 as an embodiment of the volume displacement device 700.

FIG. 1 shows a schematic view of a flow meter 1 being part of a closed-loop control system 3. The closed-loop control system 3 comprises a control unit 5. The control unit 5 is coupled to a control element 7. The control unit 5 controls the control element 7. The control element 7 and the control unit 5 are component parts of the flow meter 1. The control element 7 of the flow meter 1 can be coupled to a controlled system 9. The controlled system 9 comprises a sensor 11. The sensor 11 is adapted for measuring a controlled condition 13 of the closed-loop control system 3. The sensor 11 is coupled to the control unit 5.

The controlled condition 13 is influenced or rather dependent on a flow rate 15 of a fluidic system 17. The fluidic system 17 is also coupled to the controlled system 9 or rather to the sensor 11 of the controlled system 9. The flow rate 15 of the fluidic system 17 is a disturbance variable 19 of the controlled system 9.

The controlled condition 13 of the controlled system 9 can be, for example, the system pressure at an outlet of the fluidic system 17. The controlled condition 13 can be any other characteristic value of the flow rate 15 of the fluidic system 17, for example, the level within a container coupled to the outlet of the fluidic system 17.

The control element 7 can comprise a volumetric displacement flow meter or rather negative-displacement flow meter, for example, a piston type flow meter, wherein the control unit 5 actively controls a sucking rate 21 of the displacement flow meter. Advantageously, under the premise of a constant controlled condition 13, the amount of the actively controlled sucking rate 21 of the control element 7 of the flow meter 1 is substantially equal to the amount of the disturbance value 19 representing the flow rate 15 of the fluidic system 17.

The control unit 5 calculates a control value 23 that controls the control element 7, wherein the sucking rate 21 depends on the control value 23 according to the transfer characteristic of the control element 7. Thus, the controlled condition 13 as measured by the sensor 11 and/or a calculated control value 23 for controlling the control element 7 of the control unit 5 can be used for determining the sucking rate 21 and consequently the flow rate 15 of the fluidic system 17.

For receiving the flow rate 15, the flow meter 1 can comprise a data interface 25 as symbolized with two arrows 27. The data interface 25 can be coupled to a storage device 28, for example, adapted for storing a series of measurements, for example, for a certain period of time.

The level of the controlled condition can be selected by changing a set point 29 of the control unit 5 of the closed-loop control system 3.

FIG. 2 shows a schematic view of a fluidic system 17 coupled to a flow meter 1 comprising a closed-loop control system 3. The closed-loop control system 3 of the flow meter 1 comprises a pressure sensor 31 coupled to and arranged downstream of the fluidic system 17 via a first conduit 33, a multiplexer comprising a Y-junction valve 35, and a second conduit 37. The flow direction within the conduits 33 and 37 is indicated with arrows 39.

The Y-junction valve 35 can be adapted for branching off, for example by multiplexing and/or branching off a continuous flow, a variable percentage of a flow of the flow source 45. Thus, not the complete flow delivered by the flow source has to be sucked into the metering device for determining the flow rate of the flow source 45. Due to the known percentage branched off, the flow rate of the flow source can be calculated. Such known percentage can achieved by time slices (pulse width modulation). Advantageously, the metering device can be designed for a lower sucking rate. In other embodiments, the multiplexer can comprise a plurality of inlets and/or a plurality of outlets, for example for coupling a plurality of flow sources 45 to a plurality of flow meters 1. For example, one flow source can be measured and/or checked after the other. Furthermore, the multiplexer can be used for coupling the flow source 45 to any other downstream device, for example, to a mass spectrograph. Advantageously, a quick performance check can be executed at a point of time when the mass spectrograph has not to be fed by the flow source. Thereafter, the mass spectrograph can be coupled to the flow source again.

The fluidic system 17 can be adapted for analyzing a fluid containing a fluidic sample, for example, with a high performance liquid chromatography process. For this purpose, the fluidic system 17 can comprise a chromatographic column 40 and a detection area 41. The chromatographic column 40 can be coupled to and arranged downstream of a flow source 45, for example to a high-pressure pump, via a third conduit 43. The flow source 45 can comprise a high-pressure meter pump system, for example, comprising one or more pistons, and/or comprising a combination of a master and a slave pump. Due to the high pressure needed for the chromatographic column 40, undesired side effects can occur in the flow source 45. This can lead to an undesired inaccurate flow rate 15 of the flow source 45. An inaccurate flow rate 15 can reduce the quality of the analysis executed with the fluidic system 17. Advantageously, such side effects can be minimized by calibrating the flow source 45, for example, over a gradient of two fluids delivered by the flow source 45. For this purpose, the flow accuracy of the flow rate 15 of the flow source 45 can be measured by the flow meter 1.

For measuring the flow rate 15 of the flow source 45, the flow meter 1 comprises a two-piston metering device 47 coupled to and arranged downstream of the pressure sensor 31 via a fourth conduit 49, a rotary valve 51 and a fifth and sixth conduit 53 and 55.

The rotary valve 51 comprises four ports 57, wherein two of each are coupled by two channels 59. The rotary valve 51 couples the fourth conduit 49 alternatively to a first pumping chamber 61 via the fifth conduit 53 and to a second pumping chamber 63 via the sixth conduit 55. Besides this, each of the pumping chambers 61 and 63 are coupled alternatively to a waste 65 via a seventh conduit 67.

Consequently, one of the pumping chambers 61 and 63 is coupled to the fluidic system 17 and the other one of the pumping chambers 61 and 63 is coupled to the waste 65. In FIG. 2, the rotary valve is shown in a position, wherein the first pumping chamber 61 is coupled to the waste 65 and the second pumping chamber 63 is coupled to the fluidic system 17. A second operating position 69 of the rotary valve 51 is indicated in FIG. 2 on the left hand side of the rotary valve 51. In the operating position 69, the second pumping chamber 63 is connected to the waste and the first pumping chamber 61 is connected to the fluidic system 17.

The rotary valve 51 is set by an actuator 71 controlled by a control unit 5 of the closed-loop control system 3 of the flow meter 1.

The pumping chambers 61 and 63 are component parts of the metering device 47 of the flow meter 1. The metering device 47 is realized as a two-piston metering device. The metering device 47 comprises a first piston 75 and a second piston 77 each actuated by a screw link actuator 79. The screw link actuators 79 of the metering device 73 are each coupled to one gear 81. The gears 81 mesh with each other, thus the screw link actuators 79 of the pistons 75 and 77 can be rotated oppositely. Consequently, the pistons 75 and 77 can be actuated opposite in direction as indicated with two double arrows 83, for example, in a blockwise, rectangular motion sequence.

One of the gears 81 of the screw link actuators 79 meshes with a drive gear 85 coupled to a servo drive 87 of the metering device 73. The servo drive 87 of the metering device can comprise, for example, an electro motor controlled by the control unit 5. In other words, the control unit 5 can control the motion sequence of the pistons 75 and 77 of the metering device 73. For this purpose, the control unit 5 can calculate the motion sequence of the pistons 75 and 77 as a control value 23 of the control unit 5 of the closed-loop control system 3 of the flow meter 1.

Besides this, the control value 3 can comprise the position of the servo drive 87, the velocity of the servo drive 87, the positions of the pistons 75 and 77, and/or the velocity of the piston 75 and 77. Besides this, the flow meter 1 or rather the piston 75 and 77 of the flow meter 1 can comprise a negative force feedback with a force sensor, wherein any force exerted to the pistons exceeding a limit value effects a movement of the pistons reducing said force. For example, the force exerted to the pistons 75 and 77 can be a control value of the control unit 5. The force exerted on the pistons 75 and/or 77 is a characteristic value of the pressure within the fifth and sixth conduit 53 and 55 coupled to the pumping chambers 61 and 63. Advantageously, thus the pressure sensor can be integrated in the metering device 47 and/or in the servo drive 87 of the metering device 47. For example, the current flow rate can be determined by interpreting the actual position of the servo drive 87, for example, by the control unit 5.

The pistons 75 and 77 protrude into the pumping chambers 61 and 63 and displace the volume of the pumping chambers 61 and 63.

The pressure sensor 31 is coupled to the control unit 5 and measures a controlled condition 13, the system pressure of the fluidic system 17 between the chromatographic column 9 and the metering device 47.

Thus, the second and the third conduits 37 and 49, and the pressure sensor 31 realize a—pressure—controlled system 9. For adjusting the controlled condition 13—the pressure—the control unit 5 controls the servo drive 87, the rotary valve 51 via the actuator 71, and the Y-junction valve 35. For receiving the flow rate 15 of the flow source 45, the flow meter 1 or rather the control unit 5 of the flow meter 1 comprises a data interface 25 as indicated in FIG. 2 with an arrow 27. The control unit 5 can be coupled via the interface 25 to a mass storage device 28. The mass storage device 28 can sore a measurement series.

FIG. 3 shows a schematic view of the closed-loop control system 3 of the flow meter 1 of FIG. 2. The transfer characteristics of the single components of the closed-loop control system 3 of the flow meter 1 are indicated in the according rectangles. The Y-junction valve 35 is not shown. As can be seen in FIG. 3, the flow rate 15 generated by the flow source 45 is the disturbance variable of the closed-loop control system 3 of the flow meter 1. Any changes of the flow rate 15 effects the system pressure measured by the pressure sensor 31. The pressure, the controlled condition 13 is measured by the pressure sensor 31 and stabilized by the control unit 5, wherein the metering device 47 and the rotary valve 51 realize the control element 7 of the closed-loop control system 3 of the flow meter 1. By stabilizing the system pressure, the sucking rate 21 of the metering device 47 is indirectly adjusted to the amount of the flow rate 15 generated by the flow source 45, but with the opposite sign. Consequently, with the transfer characteristics of the servo drive, the screw link actuators, the rotary valve 51, and the pressure sensor 31, the flow rate of the flow source can be back-calculated out of the control value 23 and the controlled condition 13, the system pressure—for example as set and/or as measured—of the control unit 5 and can output via the interface 25 of the control unit 5.

FIG. 4 shows a graph 89 of a gradient profile starting with 100% water and ending with 100% acetonitrile. An x-axis 91 represents the time between 0 and 60 minutes, wherein a second x-axis 93 and a y-axis 95 represent the concentration of acetonitrile in percent.

FIG. 5 shows a graph 97 of the system pressure of the fluidic system 17 supplied with the gradient profile of FIG. 4 by the high-pressure flow source 45 of the fluid delivery system 45. The x-axis 91 represents the time between 0 and 60 minutes. A y-axis 99 represents the system pressure depending on the gradient as shown by the graph 89 of FIG. 4. As can be seen in the graph 97 of FIG. 5, the system pressure increases slightly from approximately form 500 bar to 550 bar while increasing the concentration of acetonitrile from 0% to approximately 20%. A further increase of the concentration causes a rapid pressure drop from approximately 550 bar to approximately 250 bar. This pressure behavior can be explained in particular by changes of the viscosity of the mixture of the two fluids dependant on the composition.

FIG. 6 shows a graph 101 of a flow accuracy of said fluidic system 17 in percent measured by the flow meter 1. The x-axis 91 represents the time-axis between 0 and 60 minutes. A y-axis 103 represents the accuracy of the flow rate 15 of the flow source 45 as a function of the time and of the gradient of composition as represented by the graph 89 of FIG. 4. It can be seen that the pressure variation as shown by the graph 97 of the FIG. 5 together with other side effects causes a deviation of the desired flow rate 15 approximately up to minus 2.5%. The graph 101 of FIG. 6 can be obtained by the flow meter 1 as a function of time and of the gradient as shown in the graph 89 of FIG. 4.

Advantageously, the graph 101 of FIG. 6 can be used for calibrating the high-pressure flow source 45 of the fluidic system 17. For this purpose, the fluidic system 17 can comprise a not shown control unit adapted for correcting the side effects caused by mixing and compressing the fluids water and acetonitrile as depicted in the graph 101 of FIG. 6.

The actuator 71 of the rotary valve 51 can comprise an incremental encoder. The pressure sensor 31 can be realized as a high-pressure sensor. The pressure control routines of the control unit 5 tune the flow value (as a negative flow) or rather the sucking rate 21 of the metering device 47 of the flow meter 1. The flow value can be recorded, for example, by the mass storage device 28, wherein a data trace, for example the graph 101 of FIG. 6 can be generated. The data can be generated, for example, with a system clock as short as 100 Hz.

Advantageously, the flow meter 1 can be used as a diagnostic feature to catch any undesired leakage flow of the fluidic system 17. The calibration routines, for example, based on the graph 101 as show in FIG. 6, can reach an accuracy of the flow source 45 as less as 0.1%. Besides this, a backlash compensation correction can be realized, for example, up to 60 nl total volume. Furthermore, the flow meter 1 can be used as a safety feature, for example, for detecting power fail, overpressure, and so on. Finally, a special wakeup routine on LS-indicator can be realized.

Advantageously, a pressure control valve is not necessary because the control unit 5 can adjust any desired set point 29 as the measuring pressure. For example, the system can be operated at higher pressure. By this, any undesired gassing of the fluid delivered by the flow source 45 can be avoided. The flow rate can be measured at the same pressure as at the end of the chromatographic column 39 or at any desired higher pressure adjustable by the closed-loop control system 3 of the metering device 1. For example, at zero pressure differential to reference value, for example ambient pressure, to prevent any undesired leakages of the control element (7).

Advantageously, the metering device of the flow meter can be used as described above or as a reference flow source. For this purpose, the flow meter can be coupled with a fluid delivery system, for example, a fluid container.

The fluidic system 17 can be adapted for analyzing liquid. More specifically, the fluidic system 17 can be adapted for executing at least one microfluidic process, for example an electrophoresis and/or a liquid chromatographic process, for example a high performance liquid chromatographic process (HPLC). Therefore, the fluidic system 17 can be coupled to a liquid delivery system 45, in particular to a pump, and/or to a power source. For analyzing liquid or rather one or more components within the liquid, the fluidic system 17 can comprise a detection area 41, such as an optical detection area and/or an electrical detection area being arranged close to a flow path within the fluidic system 17. The fluidic system 17 can be coupled to the flow meter 1 for determining or measuring the flow rate of the liquid delivery system 45. Otherwise, the fluidic system 17 can be coupled to a laboratory apparatus, for example to a mass spectrometer, for analyzing the liquid. For executing an electrophoresis, the flow path can comprise a gel. Besides this, the fluidic system 17 can be a component part of a laboratory arrangement.

FIG. 7 shows an embodiment, wherein the metering device of the flow meter 710 comprises a volume displacement device 700. The volume displacement device 700 is adapted for displacing a defined volume of the intaken fluid received at its input 720. Such volume displacement device 700 might be or comprise a gear pump, a toothed wheel pump (as shown e.g. in FIG. 9), a worm gearing, a worm gear drive, etc. The volume displacement device 700 in the example of FIG. 7 is driven by a drive (as indicated by arrow 730) for actively driving the volume displacement. The drive 730 is controlled by the control unit 740 and allows for compensating a pressure drop according along the volume displacement device 700 otherwise resulting e.g. from leakages or mechanical and/or hydraulic friction within the volume displacement device 700.

The control unit 740 receives an input pressure value Pi (from a pressure sensor 750) indicative of an input pressure at the input 720 of the volume displacement device 700. The control unit 740 in the example of FIG. 7 further comprises a comparator 760 having as inputs the input pressure value Pi and a preset pressure value Pp. The control unit 740 thus controls the fluid intake of the metering device in response to the received input pressure value Pi by comparing the received input pressure value Pi with a preset pressure value Pp und controlling the volume displacement device 700 based on a difference between the received input pressure value Pi and the preset pressure value Pp.

The control unit 740 might further comprise an amplifier 770 adapted for converting the output signal of the comparator 760 into corresponding energy required for driving the drive 730.

In the example of FIG. 7, the flow meter 710 is coupled to an output of an HPLC device 780 and its output 790 might be coupled to any kind of adequate fluid containing device 795 such as a fluid fractionator or a waste. Thus the flow meter 710 allows monitoring the (actual) flow rate of the fluid flow streaming at the output 720 of the HPLC device 780.

FIG. 8 shows a further embodiment, wherein the control unit 740 receives as second input an output pressure value Po measured by a pressure sensor 800 at the output 790 and being indicative of the pressure at the output 790. The control unit 740 controls the fluid intake of the volume displacement device 700 in response to the received input Pi and output Po pressure values. In the example of FIG. 8, the comparator 760 compares both the input Pi and output Po pressure values and provides a control signal at its output in response to a difference between the received input Pi and output Po pressure values. In the example of FIG. 8, a further comparato 810 might compare the difference signal to a setpoint value (Δ Pp) being coupled between the comparator 760 and the amplifier 770 in order to allow controlling the volume displacement device to act for achieving a preset differential pressure. This differential pressure may include the value of zero.

In the example of FIG. 8, the flow meter 710 is coupled between the output of the HPLC device 780 and a hydraulic load 820. This hydraulic load might comprise one or more of: an HPLC sampling device; an HPLC separation column; a fraction collector; or just a certain length of passage tubing. The hydraulic load 820 might then be coupled to the fluid containing device 795, which might also be or comprise a sink. Thus the flow meter 710 allows monitoring the (actual) flow rate of the fluid flow streaming into the hydraulic laod 820 at a certain working pressure.

In both FIGS. 7 and 8, the data output (data interface) of the flow meter 710 is indicated by the arrow 27, so that any kind of data output, e.g. a value of flow rate, can be provided to and used by one or more units external to the flow meter 710.

FIG. 9 shows a gear pump (or toothed wheel pump) 900 as an embodiment of the volume displacement device 700. The gear pump 900 comprises two meshing gears 910 and 920 (in a housing 930) to pump incoming fluid 940 by displacement. The gear pump 900 has a fixed displacement, thus pumping a constant amount of fluid for each revolution, or a portion thereof, of the gears 910 and 920. As the gears 910 and 920 rotate they separate on the intake side of the pump, creating a void and suction which is filled by fluid. The fluid is carried by the gears 910 and 920 to the discharge side 790 of the pump 900, where the meshing of the gears 910 and 920 displace the fluid. The mechanical clearances are preferably designed to be as small as possible, as tight clearances, along with the speed of rotation, effectively prevent the fluid from leaking backwards. A rigid design of the gears 910, 920 and the housing 930 allow for very high pressures and the ability to pump highly viscous fluids.

Other types of gear pumps 900 might be used accordingly, e.g. as the gear pumps disclosed in U.S. Pat. No. 5,184,519 A, U.S. Pat. No. 4,409,829, U.S. Pat. No. 4,815,318, WO 2005/119185 A1, or U.S. Pat. No. 6,658,747 B2.

Readout of the actual displacement rate can be done by monitoring the driving speed of the volume displacement device 700 or a sensing device may be employed, which records the actual speed or volumetric displacement.

It is to be understood, that embodiments described are not limited to the particular component parts of the devices described or to process features of the methods described as such devices and methods may vary. It is also to be understood, that different features as described in different embodiments, for example illustrated with different Fig., may be combined to new embodiments. It is finally to be understood, that the terminology used herein is for the purposes of describing particular embodiments only and it is not intended to be limiting. It must be noted, that as used in the specification and the appended claims, the singular forms of “a”, “an”, and “the” include plural referents until the context clearly dictates otherwise.

Claims

1. A flow meter comprising a metering device adapted for intaking and metering a defined volume of a fluid, anda control unit adapted for controlling the fluid intake of the metering device for determining a flow rate of the fluid.

2. The flow meter of claim 1, wherein the sucking rate of the metering device is a control variable or a dependent variable of one or more control variables of the control unit.

3. The flow meter of claim 1, wherein the metering device comprises at least one of: a pumping chamber, wherein preferably the volume of the pumping chamber is a control variable of the control unit;a piston projecting into the pumping chamber,two pistons and a valve adapted for metering a substantially continuous flow.

4. The flow meter of claim 1, comprising at least one of: at least one of the position and the velocity of the piston/s is a control variable of the control unit;at least one of the position and the velocity of a servo drive adapted for actuating the piston/s and coupled to the piston/s is a control variable of the control unit;the motion sequence of the two pistons and the operating position of the valve are control variables of the control unit;the valve is a rotary valve and comprises two operating positions.

5. The flow meter of claim 1, comprising a displacement device, at least partly capable of precise displacement,wherein preferably the displacement of the displacement device is a control variable of the control unit.

6. The flow meter of claim 1, comprising at least one of: the admission pressure of the metering device is a controlled condition of the control unit,the flow rate of a flow source connected to the metering device is determinable as a dependent variable of the control variable/s and the controlled condition of the control unit,the flow rate of the flow source is determinable as a dependent variable of the motion sequence of the two pistons, the operating position of the valve, and the admission pressure,the sucking rate of the metering device is adjustable to a value substantially equal to the flow rate of the flow source connected to the metering device.

7. The flow meter of claim 1, wherein: the metering device comprises at least one of a multiplexer and an inlet Y-junction valve, adapted for branching off a variable percentage of the flow rate of the flow source.

8. The flow meter of claim 7, wherein the multiplexer is adapted for coupling at least one of: a plurality of flow sources to the metering device,a plurality of metering devices to the flow source,the plurality of flow sources to the plurality of metering devices,the flow source or the plurality of flow sources to a device or to a plurality of devices.

9. The flow meter of claim 1, wherein the metering device comprises a volume displacement device adapted for metering the defined volume of the fluid by displacing the defined volume of the intaken fluid.

10. The flow meter of claim 9, wherein the control unit receives an input pressure value indicative of an input pressure at the input of the metering device, and the control unit is adapted to control the fluid intake of the metering device in response to the received input pressure value.

11. The flow meter of claim 10, wherein the control unit receives an output pressure value indicative of an output pressure at the output of the metering device, and the control unit is adapted to control the fluid intake of the metering device in response to the received output pressure value, preferably in response to a difference between the received input and output pressure values.

12. The flow meter of claim 9, wherein the volume displacement device comprises one of a gear pump, a toothed wheel pump, a worm gearing, and a worm gear drive.

13. The flow meter of claim 9, wherein the volume displacement device comprises a drive for actively driving the volume displacement as controlled by the control unit.

14. The flow meter of claim 9, wherein the volume displacement device is one of a microfluidic device and a micromechanically made device.

15. A fluidic system adapted for analyzing a fluid, comprising: a flow meter of claim 1;a fluid separation device for housing a fluid sample and for separating components of said fluid for analysis, anda fluid delivery system, in particular a flow source, in particular a high-pressure fluid delivery system.

16. The fluidic system of claim 15, comprising at least one of: the fluid separation device comprises a chromatographic column adapted for separating components of a sample delivered by flow from said fluid delivery system, wherein said chromatographic column is fluidically coupled to said flow meter;a detection device adapted for detecting said separated components within said fluid;a chromatographic system,a high performance liquid chromatographic system,an HPLC arrangement comprising a chip and a mass spectrograph,a high throughput LC/MS system,a purification system,a micro fraction collection/spotting system,a system adapted for identifying proteins,a system comprising a GPC/SEC column,a nanoflow LC system,a multidimensional LC system adapted for separation of protein digests,a parallel LC system.

17. A method of determining a flow rate with a flow meter having a metering device adapted for intaking and metering a defined volume of a fluid, and a control unit adapted for controlling the fluid intake of the metering device for determining a flow rate of the fluid, the method comprising: controlling the fluid intake of the metering device adapted for intaking and metering a defined volume of a fluid.

18. The method of claim 17, comprising at least one of: monitoring a drive speed of the flow meter, in particular the drive speed of a displacement device of the flow meter;monitoring an actual speed of movement of the flow meter;monitoring a cycle time of the flow meter, wherein preferably the cycle time is inverse proportional to the flow rate;monitoring an actual position of the flow meter over time to derive its speed.integrating the metered volume.

19. A software product, encoded on a computer readable medium, for executing the method of claim 17, when run on a data processing system.