MXPA98008139A - Liqui meter - Google Patents

Abstract

A meter (2), for measuring the volumetric flow rate of a liquid, for example, water, is formed with a pipe (4), forming a flow path of the liquid containing a low-energy electric heater (12). A temperature sensor (19) measures the temperature T1 of the liquid adjacent an end upstream of the heater and a temperature sensor (20) measures the temperature T2 of the liquid adjacent to a downstream end of the heater. The heater (12) adds heat energy from a P value to the liquid. A control installation (18), comprising computing means calculates the flow rate Q using expression (a) where ST1 and DT1 are the specific heat capacity of the liquid and the density of the liquid respectively, at the measured temperature T1 by the detector (1

Description

METHOD OF LIQUIDS Field of the Invention This invention relates to a liquid meter and in particular the invention relates to a method for measuring the volumetric flow rate of a liquid flow along a path and also refers to a liquid meter to measure the volumetric flow rate of a liquid flow along a trajectory. The liquid can be water. Background of the Invention Conventional water meters use a variety of technologies. They can use turbines or other rotating elements that are responsible for the volume of water flow and have a known feature related to the flow rate for the rotational speed of the turbine. 0 can use the ultrasonic speed measurement, when the "duration of the path" between the transmission and reception of an ultrasound pulse is related to the speed of the water flowing. 0 can use the electromagnetic velocity measurement, where the average velocity of the magnetic particles passing or ions suspended in the water are related to a measurement of the flow in large volume.

Existing low-cost flow meters, particularly those suitable for measuring domestic water consumption, suffer from a number of deficiencies, including poor reliability and poor accuracy. The problem of reliability is mainly due to the susceptibility of existing technologies to the pollutants that are deposited from the water supply over a long period. Turbine meters are particularly susceptible to oxidation, which affects the friction of the support / shaft, this problem most likely affecting the calibration for low flow rates. However, electromagnetic meters can also be affected by use, very clean deionized water, where measuring principles do not operate at all. Poor accuracy can be caused in part by pollutants, partly by poor facilities and partly by the particular technology used. Oxidation will affect the calibration of the turbine, ultrasonic and electromagnetic meters, due to the change in the dimensions of the flow channels, which in turn affect the velocities of the fluids for a flow rate volumetric given. The characteristics of the turbine impeller will also be altered by the increase in oxidation. Installation errors can affect the accuracy of all water meters that measure speed. Particular care should be taken to ensure that sufficient sections of straight pipe are installed both upstream and downstream of the meter. The limited operational range of the flow measurements provided by many conventional water meters can cause large errors, particularly when the meters are thicker than the particular installation or when the actual flow rates vary over a wide range. High costs must be paid for acceptance and reliability. It has been estimated that for a utility water meter with + or - 1% accuracy, similar to that provided by a gas or electricity meter, the price is as much as five to ten times. Even with such an investment, long-term reliability is unlikely to be as good as that provided by gas or electricity meters. The experience of unreliability of the meters is indicated by the requirements in Germany that all water meters must be withdrawn from service every five years for its re-calibration and maintenance, if they are used for billing purposes. SUMMARY OF THE INVENTION It is an object of the invention to provide a method of measuring the volumetric flow rate of a liquid, in which if the liquid must be water, it avoids the aforementioned disadvantages. Another object is to provide a liquid meter which if used to measure the volumetric flow rate of water, avoid the disadvantages mentioned above. According to a first aspect of the invention there is provided a method of measuring the volumetric flow rate of the liquid flowing along a path comprising adding heat from a value of heat energy P to the liquid at a location on said path , measuring a temperature difference value (T2-Ti) between a temperature Tx of the liquid in said path in a first position adjacent to an extremity upstream of said location and a temperature T2 of the liquid in said path in a second position adjacent to the extremity downstream of said location, being upstream and downstream with respect to the direction of the flow of the liquid passing said location and calculating the flow velocity volumetric Q of the liquid according to the expression: PQ = STjxDTl-x (T2-Tl) where STX is the specific heat capacity of the liquid in said first position and DTi is the density of the liquid at the temperature of said liquid in said first position. According to a second aspect of the invention there is provided a liquid meter for measuring the volumetric flow rate of a liquid comprising a path for the flow of the liquid along the same, means of adding heat to add heat of the liquid. a value of heat energy P to said liquid at a location in said path when the meter is in use, means of measuring the temperature difference to measure a temperature difference value (T2-Ti), when the meter is located in use, between a temperature Ti of the liquid in said path in a first position adjacent an end upstream of said location and a temperature T2 of the liquid in said path in a second position adjacent to a downstream end of said location, being waters up and downstream with respect to the direction of the liquid flow passing said location when the meter is in use and means for ac Calculate the proportion of the volumetric flow Q of the liquid according to the expression: P STjxDT, lx (T2-Tl) 'where STX is the specific heat capacity of the liquid in said first position and DTX is the density of the liquid at the temperature of the liquid in said first position. BRIEF DESCRIPTION OF THE DRAWINGS Each aspect of the invention will now be described further with reference to the accompanying drawings in which: Figure 1 shows diagrammatically and partially in section, a mode of a liquid meter for measuring the proportion of volumetric flow of a liquid according to the second aspect of the invention and capable of carrying out the method according to the first aspect; Figure 2 is a graph showing the variation of density DTX (in kg per m3) of water with water temperature in degrees Celsius ° C and shows the variation of specific heat STi (in Joules J per kg per ° C) of water with water temperature in ° C and Figure 3 is a graph showing the variation of a K factor (in J per m3 per ° C) for water with the water temperature in ° C where K = STi x DTi Detailed Description of the Invention With reference to the accompanying drawings a volumetric liquid flow rate meter 2 comprises a path or pipe 4 which can be surrounded by a good thermal insulation 6 and can be adapted to each end for example by means of threads 8 and 10 for connection through suitable couplers in a supply line through which the liquid is supplied. The liquid may be water and the aforementioned supply line may be a water main; in this way, the meter 2 can be a water meter. The main water pipe can lead to real estate, for example, domestic real estate, in which case the meter 1 is a domestic water meter. The liquid to be measured enters the pipe 4 in the direction of the arrow A and leaves in the direction of the arrow B. Inside the pipe 4 there is an electric heater 12 preferably a low energy heater which, for example, may have an amperage of the order of five watts. The heater 12 is provided with electric power from a suitable power supply 14 operated in response to signals on the signal path 16 from a control facility 18 which may be an electrical or electronic apparatus comprising computing means that serve as calculation means. A temperature sensor 19 is mounted in the pipe 4 upstream of the heater 12 and another temperature sensor 20 is mounted in the pipe downstream of the heater. In this way the heater 12 is mounted in the pipe 4 at a location between the two temperature detectors 19, 20 which are placed adjacent to opposite ends of the location in which the heater adds heat to the liquid. The temperature detectors 19, 20 are electrical or electronic devices that provide signals, in the signal paths 22, 24 respectively, representative of the temperatures of the fluid that are observed inside the pipe 4. The temperature detectors 19, 20 are preferably Precise and also preferably have a high resolution eg an ability to accurately measure small increments of eg 0.001 ° C. The temperature of the liquid observed by the detector 19 is Ta degrees Celsius (° C) and that observed by the detector 20 is T2 ° C. The heat input to the liquid through the heater 12 is P watts. In detector 19 the density of the liquid is DTX in kg / m3 and the capacity of Specific heat is STi in J / kg / ° C. The control installation 18 calculates the volumetric flow rate Q of the liquid in cubic meters (m3) per second according to the expression The control installation 18 is programmed with an expression by means of which the variable value of STixDTi with variation in the measured temperature Ti, can be calculated or the control installation can be provided with a look-up table that provides the respective values for ST? XDT: for different observed values of Ti. The how such information can be obtained by the provision to the control facility 18, can be understood from figures 2 and 3 which refer to water as the liquid being measured. In Figure 2 the variation of the water density DTi with the temperature Ti is shown as a variation of the specific heat capacity STi with the temperature Ti. K = STixDTi so that from Figure 2, the value of K for the respective values of Ti can be calculated and represented by the graph in Figure 3. For example, when the water temperature Ti is 10 ° C, K has a value of approximately 4200 x 103 J / m3 / ° C. The control installation 18 can send signals on the path 26 towards a recording and / or display means 28 which gives a record or indication of the liquid flow rate at that moment and the control installation can integrate the successive calculated P values of the volumetric flow rate with with respect to the time and signals sent on the trajectory 26 for recording or displaying the quantity of liquid supplied over a period of time. Also the control facility 18 may have cost data entry thereto, so that it can calculate the monetary cost of the liquid delivered through a period and / or the monetary proportion to which the liquid is supplied and this cost and The monetary ratio can be recorded and / or displayed by means of the recording and / or display means 28. The energy output P delivered by the heater 12 can be assumed to be substantially constant or the control device 18 can calculate the value of P from the expression P = ixv, where v is the voltage across the heater, and i is the current flow through the heater; representing the signals for example, instantaneous values of v and i supplied in the path 30 to the control installation from the power supply 14. As an optional feature, the components The electric meters of the meter can be energized by means of a rechargeable battery 32, an energized liquid flow turbine 33 that is provided in line 4 for driving an electric generator 34 that supplies electric power to a battery charger 36 that charges the battery. To ensure that the accuracy of the measurement is maintained over long periods and that the low heat energy can be used, the power supply to the heater 12 can be repeatedly and regularly closed by means of the control facility 18 for a period and restored afterwards. for a period. For example, the period of ignition of the heater and the period of shutdown of the may be substantially equal, and may, for example, each be substantially five seconds in duration. Turning the heater 18 on and off allows the temperature detectors 19, 20 to be calibrated. When the heater 12 is turned off the temperature readings of the detectors 19 and 20 will be the same, ie Ti and thus the expression T2-Ti must be zero. But there may be a difference or error e, between the value Tx and the value T2 because the detectors 18 and 20 do not give identical outputs, so that T2 = Ti ± e. The control facility 18 subtracts Ta from T2 to give the error e, which is + e, if the value of T2 is less than that of Ti (the detector 20 is read low, compared to the detector 19) and -e if the value of T2 is greater than Ti (detector 20 is read high compared to detector 19). The next time the heater 12 is turned on and the temperature readings of the detectors 19 and 20 are Ti and T2 respectively, then the control installation 18 calculates the temperature that through the heater between the two detectors as T2-Ti + e when the detector 20 is read low and as T2-Ti-e when the detector 20 is read high. The output signal from each detector 19 and 20 can be recorded by the control facility 18, and the temperature difference between the detectors, when the heater 12 is turned on, is calculated when, over a predetermined period of time successively differences in temperature are recorded. temperature during a heater firing period, all falling within a predetermined tolerance; those successively recorded temperature differences are averaged and the average value is used as the difference (T2 - Ti) in expression (1) above. To allow a wide reduction in the proportions of the liquid flow to be supplied without causing excessively high electrical signals to occur as a result of the elevated temperature measurements by the detector 20, the energy P of the heater can be controlled by means of the control installation 18 to avoid the high signals that are produced. Both the magnitude of the heater power P and the on / off duration can be altered for each on / off cycle of the heater operation following the achievement of a stable temperature difference of the liquid through the heater 12 between the heaters. detectors 19 and 20. The magnitude of the energy P of the heater varies from a relatively high predetermined value, (but still only a few watts) to a relatively high predetermined flow rate, down to a relatively low predetermined value at a relatively low predetermined flow rate to ensure that the temperature difference (T2-Ti) is substantially the same at both ends of the flow. The firing duration of the heater can be reduced to low flow rates because the temperature T2 observed by the downstream detector 20 achieves a higher value in a shorter time than when the flow ratios are high. The volumetric flow meter 2 as described above has several advantages. They are: A A wide reduction in flow can be measured accurately. In contrast to conventional measurement technology the accuracy for meter 2 is Increase in low flows. The reason for this increased accuracy is that as the flow is reduced, the temperature difference (T2 - Ti) will rise for a given constant value of the energy P of the heater. B The contaminant deposits of the fluid inside the meter 2 for a long period of time will not affect the accuracy of the measurement. This is because when the internal surfaces become contaminated, the injected heat will still reach the fluid and consequently the detector 20 downstream, although the time taken for heat transfer can be increased. In addition, the relationship: p Q = STjxDT lx (T2-Tl) 'is independent of the flow velocity and the cross-sectional area of pipe 4, hence oxidation will have no effect on the determination of Q. C The meter 2 It is able to correct variations in specific heat capacity and water density as the temperature varies. D The final cost of making the meter 2 can be competitive with existing technologies, since mechanical components and electronic detectors can be used, simple with non-movable parts (without considering the turbine 32 and the generator 34, the use of such it is not essential). E Reliability can be raised as moving parts are not used. F For the required accuracy of + or -1% the "extraordinary calibration" will not be necessary The default calibration of the detector, the energy measurements of the heater and the pre-programmed values of the coefficient (ST1XDT1) were already provided resulting in considerable savings of cost.

Claims (19)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and therefore the property described in the following claims is claimed as property. A method for measuring the volumetric flow rate of a liquid flowing along a path comprising adding heat of a P value of heat energy to the liquid at a location on said path, measuring a difference value of temperature (T2-Ti) between a temperature Ti of the liquid in said path in a first position adjacent an end upstream of said location and at a temperature T2 of the liquid in said path in a second position adjacent to a downstream end of said location , being upstream and downstream with respect to the direction of the flow of the liquid passing said location and calculating the proportion of the volumetric flow Q of the liquid according to the expression: P STJXDTJx (t2-Tl) 'where ST2 is the specific heat capacity of the liquid in said first position and DTi is the density of the liquid at the temperature of said liquid in said first position.
2. 2. A method according to claim 1, characterized in that, the temperature Tx is measured using first temperature sensing means upstream of said location and the temperature T2 is measured using second temperature sensing means downstream of said location, the addition of intermittent heat being and during an interruption in the addition of heat are calibrated the temperature measurements of the first and second means of temperature detectors.
3. 3. A method according to claim 1 or 2, characterized in that the term (T2-Ti) used in the expression is an average of a plurality of successive measurements of the temperature difference (while the heat is added at said location) between the first and second positions found to be within a pre-determined tolerance.
4. A method as claimed in any of the preceding claims, characterized in that the heat is added for periods of time that are shorter when the flow rate of the liquid is low compared to the length of the periods of time during which The heat is added when the flow rate of the liquid is higher.
5. 5. A method as claimed in any of the preceding claims, characterized in that the liquid flow rate Q is integrated with respect to at the time to give a volume of liquid that has passed along the trajectory in a period of time.
6. 6. A method according to claim 5, characterized in that the data of the flow rate Q and the monetary cost data are used to calculate the monetary value of the liquid that passes along the trajectory in said period of time.
7. 7. A method as claimed in any of the preceding claims, characterized in that the liquid is water.
8. 8. A method for measuring the volumetric flow rate of a liquid flowing along a path, substantially as described hereinabove with reference to the accompanying drawings.
9. 9. A liquid meter for measuring the volumetric flow rate of a liquid comprising a path for the flow of the liquid therethrough, means that add heat to add heat of a P value of heat energy to said liquid in a location in said path when the meter is in use, means of measuring temperature difference to measure a temperature difference value (T2-Ti), when the meter is in use, between a temperature Ti of the liquid in said temperature path in a first position adjacent to one end upstream of said location and at a temperature T2 of the liquid in said path in a second position adjacent to a downstream end of said location, being upstream and downstream with respect to the direction of the liquid flow passing said location when the meter is find in use and means of calculation to calculate the proportion of the volumetric flow Q of the liquid according to the expression: P STjxD lx (T2-Tl) 'where STi is the specific heat capacity of the liquid in said first position and DTi is the density of the liquid at the temperature of the liquid in said first position.
10. A liquid meter according to claim 9, characterized in that the control means comprise said calculation means, the temperature difference measuring means comprising first temperature sensing means in said first position and second temperature sensing means in said second temperature. position, the control means being installed to cause the heat-adding means to add heat and to interrupt the addition of heat by said means adding heat, and the control means to calibrate the temperature readings of the first and second temperature sensing means while means adding heat is interrupted.
11. 11. A liquid meter according to claim 10, characterized in that the heat adding means comprises an electric heater in said path.
12. 12. A liquid meter according to claim 10 or claim 11, characterized in that the control means are installed to deduce the term (T2-Tx) used in said expression when deducting an average of a plurality of successive measurements of the difference in temperature (while the heat adding means is adding heat) between the first and second positions found by said control means to be within a pre-determined tolerance.
13. 13. A liquid meter according to any of claims 10 to 12, characterized in that, the control means are installed to control the operation of the means that add heat in such a way that the heat is added for periods of time that are shorter when the proportion of the liquid flow is low compared to the duration of the periods of time during which heat is added when the proportion of the liquid flow is greater.
14. 14. A liquid meter according to any of claims 10 to 13, characterized in that, the control means are installed to integrate the liquid flow rate Q with respect to time to give a volume of the liquid which passes along the path in a period of time.
15. 15. A liquid meter according to claim 14, characterized in that, the control means are installed to use the data of the flow rate Q and the monetary cost data to calculate the monetary value of the liquid passing through the liquid. trajectory in said period of time.
16. 16. A liquid meter according to any of claims 9 to 15, characterized in that the path has an external thermal insulation.
17. 17. A liquid meter according to any of claims 9 to 16, characterized in that the meter uses a rechargeable battery to provide electrical energy and the battery is rechargeable rechargeable by means that charge the battery supplied with electrical energy by electric power generating means installed to act in response to the flow of the liquid along the path.
18. 18. A water meter according to any of claims 9 to 17.
19. 19. A liquid meter for measuring the proportion of the volumetric flow of a liquid, substantially as described hereinabove with reference to the accompanying drawings.