RU2296959C1 - Method for calibration of volumetric flow meters of heat counter and device for realization of said method - Google Patents

Abstract

FIELD: possible use for continuous individual and pair-wise calibration of flow meters used in heat counters.

SUBSTANCE: device contains feeding one, reverse one and block of bypass pipelines. By means of bypass pipelines, a difference of flows in feeding and reverse pipelines is created and by this movement of heat carrier in open water heating system is imitated. Pairs of flow meters being calibrated are mounted in feeding and reverse pipelines. On each bypass pipeline mounted serially are two or mote standard flow meters and a controlled adjustable valve for precise control of flow. Rough adjustment of fed difference of flows is performed by means of controllable adjustable valve, positioned on reverse pipeline. Continuous calibration of flow meters when heat carrier draining is absent is performed on basis of block of standard flow meters, configuration of which is analogical to bypass block. Device is equipped with source flow standard with flow switches and standard meters (or weights). On basis of original standard, volumetric flow meters are simultaneously calibrated in standard and bypass blocks with error ±0,15-0,3%.

EFFECT: increased precision of calibration.

2 cl, 6 dwg

Description

The invention relates to experimental measuring equipment and can be used in energy, oil, chemical industry, housing and communal services, etc.

A device for calibrating and evaluating the error of flowmeters is known. The flowchart for calibrating flowmeters of an open heat consumption system contains volumetric flow meters (water meters) of the supply and return pipelines, a hot water supply meter and a heat exchanger. Water meters and a heat exchanger are interconnected in series. The water meter in the channel (water pipeline) of hot water supply through two controlled valves is connected in parallel with the supply and return channels (pipelines). The open system device is divided into two groups: open, consisting of two controlled valves and a hot water meter, and closed with leaks (water flow), consisting of two water meters and a heat exchanger. Moreover, in the open subsystem, the amount of coolant in the water supply is determined by the reading of the water meter in this channel, and the amount of heat energy according to the equation for a one-pipe heat supply system.

This solution allows you to calibrate the volumetric flow rate of the coolant in different industries. (How to reduce the measurement of thermal energy and coolant leakage. Journal of Legislative and Applied Metrology, No. 5, 2002, pp. 6-13, author I.Yu. Sheshukov).

The disadvantages of this device: the secondary meter of the heat meter must introduce an amendment to the readings of the water meters, which increases the cost of operation. The difference between the magnitude of the new and old corrections is large and equal to 0.42 m ³ , which corresponds to an additional error in determining the magnitude of the leak. The flow rate of the coolant is measured with a high error of ± 10%. There is no possibility of continuous calibration of flowmeters. The flow meters at each metering node must be individually calibrated when changing the conditions of use, which is associated with large time costs. Only authorized persons may re-calibrate flow meters in commercial settlements. During the calibration of flowmeters, inconvenience arises with the heat supply to consumers.

A known method of calibrating volumetric flow meters of the coolant and determining the error and the amount of flow of the coolant.

где V₃ - объем по показанию водосчетчика ГВС; ρ₁₍₂₎ - плотность воды в подающем и обратном трубопроводе; h₁₍₂₎ - энтальпия в подающем и обратном трубопроводе; h_х - энтальпия холодной воды на источнике теплоты.Determine the amount of thermal energy according to the equation for a single-tube device for heat supply of hot water

where V ₃ is the volume according to the DHW water meter; ρ _{1 (2)} is the density of water in the supply and return piping; h _{1 (2)} is the enthalpy in the supply and return piping; h _x is the enthalpy of cold water at the source of heat.

The total amount of coolant leakage in the device is defined as: G = G _DHW + G _y , where G _DHW is the mass of the coolant sampled on the DHW; G _у - coolant leak in the closed subsystem of the device.

где δQ_ГВС и δQ_ЗУ - относительные погрешности в подсистеме устройств ГВС и в закрытой подсистеме устройства с утечками. Суммарное количество потребленной тепловой энергии в устройстве определяют как: Q=Q_ГВС+Q_ЗУ, где Q_ЗУ - количество тепловой энергии в закрытой подсистеме устройства с утечками.Then determine the total amount of energy consumed in the closed subsystem of the device with leaks. Then the error of the total thermal energy is determined as:

where δQ _DHW and δQ _memory are relative errors in the DHW subsystem and in the closed device subsystem with leaks. The total amount of thermal energy consumed in the device is defined as: Q = Q _DHW + Q _memory , where Q _memory is the amount of thermal energy in the closed subsystem of the device with leaks.

This solution allows you to calibrate the volumetric flow rate of the coolant (How to reduce the measurement error of thermal energy and leakage of the coolant. Journal "Legislative and Applied Metrology", No. 5, 2002, p.6-13, author. I.Yu. Sheshukov).

The disadvantage of this method is that this method is difficult to implement without additional standard methods. For this, it is necessary to carry out a major reconstruction of existing metering stations and significantly complicate the design of newly commissioned metering stations for thermal energy and the amount of coolant. In addition, the high costs for implementing the method in everyday life do not completely eliminate the large errors in the conversion coefficient of the flow meters.

Closest to the proposed invention, the technical solution is a device for calibrating volumetric flow meters of a coolant and evaluating the error of its measurement. The device comprises flow meters in the supply and return channels (pipelines). The diameters of the pipes in the supply and return channels are the same (32 mm). A flowmeter with a nominal diameter of 10 mm in the bypass channel simulates measurements in the pipeline (channel) of hot water supply (DHW). At the output of the return and DHW channels, a scale is connected. The value of the coolant flow through the flow meter of the hot water supply channel varied from 0.09 t / h to 2.8 t / h. In this case, the flow rate of the flow channel of the feed channel was selected so that the flow rate of the return channel was constant. Measurements were carried out continuously for three days.

The maximum discrepancy in weights is 23.3%, in supply pipelines 2.2%, inverse 3.3%, and hot water supply 23.4%.

This solution allows you to calibrate volumetric flow meters and evaluate calibration errors in open and closed heat supply systems (Methodological error in the linear approximation of the error characteristics of flow meters. In the symposium book "World of measurements. Water, heat, gas, November 9-11, 2004", Collection of reports, St. Petersburg, 2004, p.138-148, authors A.G. Safin, V.M. Kuzovkov).

The disadvantage of this device: the measured value of the coolant leakage by the difference between the readings of the flow meters of the forward and return channels differs up to 20% from the readings of the flow meter of the hot water supply channel, although the errors of all flow meters according to the results of individual calibration do not exceed ± 0.5%. The accuracy of determining the mass of leakage of the coolant depends on the slope of the calibration characteristic of the DHW channel.

Closest to the proposed invention, the technical solution is a method for calibrating volumetric flow meters of a coolant and assessing the error of its measurement.

The essence of the method for determining the flow rate of the coolant and the estimation of the measurement error are justified by the method of determining the characteristics of the mutual discrepancy of the measurement results through channels (pipelines). The analysis of the error in the measurement of the difference in costs is carried out using linear approximation.

- Determine the thermal energy and coolant flow in the heating system with open water in the supply pipe. The heat energy consumption Q for such a device is defined as: Q = M ₁ (h ₁ -h ₂ ) + (M _DHW + M _y ) (h ₂ -h _HV ), where M ₁ is the mass of the heat carrier passing through the supply pipe; h ₁ , h ₂ - coolant enthalpy in the supply return piping, respectively; M _DHW - the mass of the coolant according to the testimony of a water meter selected for the needs of DHW; M _y - mass leakage of the coolant; h _ХВ - enthalpy of cold water.

- The leakage mass is defined as: M _y = M ₁ -M ₂ -M _DHW , where M ₂ is the mass of the heat carrier passing through the return pipe.

- Together they solve the equations for Q and M _y and determine the consumption of thermal energy in systems with open water, i.e. Q = M ₁ (h ₁ -h ₂ ) + (M ₁ -M ₂ ) (h ₂ -h _XB ).

- Monitor the operation of the heat meter by determining the dependence of M _DHW on the increment M ₁ under the assumption that M _{DHW is} not dependent on M ₂ , i.e. device idealize.

и построение зависимости М от

.- The second approach is artificial. Bring the device to closed using the expression

and building the dependence of M on

.

где Δ(x)- взаимное расхождение величин x и y. При этом угол наклона между двух величин x и y окончательно определяют как:

Если величина взаимного расхождения не зависит от x, то угол наклона всегда равен 1. В этом случае невозможно оценить взаимное расхождение показаний. Если Δ(x_i)=δx_i, то угол наклона прямой характеризует величину взаимного расхождения, β=1+δ. Если величина взаимного расхождения переменна, то угол наклона зависит от характера этой зависимости.- Further, it is assumed that the increment of y depends on the increment of x in accordance with the expression:

where Δ (x) is the mutual discrepancy between the quantities x and y. In this case, the angle of inclination between the two quantities x and y is finally determined as:

If the magnitude of the mutual discrepancy does not depend on x, then the angle of inclination is always 1. In this case, it is impossible to estimate the mutual discrepancy of the readings. If Δ (x _i ) = δx _i , then the slope of the line characterizes the magnitude of the mutual discrepancy, β = 1 + δ. If the magnitude of the mutual discrepancy is variable, then the angle of inclination depends on the nature of this dependence.

по выражению:

, где

. Зависимость β_i от k почти гиперболическая.- Assume that at points x _{i the} relative positions of x and y are Δ (x _i ) = 0.009x _i ; and at the point x _{i + 1} -Δ (x _{i + 1} ) = - 0.009x _{i + 1} . Then the angle of inclination depends on the width

by expression:

where

. The dependence of β _i on k is almost hyperbolic.

This method allows you to calibrate volumetric flow meters for heat meters and to evaluate the errors of their measurements in open and closed heat supply systems (Methodological error in the linear approximation of the error characteristics of flow meters. In the symposium "World of measurements. Water, heat, gas. November 9-11, 2004 "Collection of reports. St. Petersburg, 2004, p.138-148. Authors Safin AG, Kuzovkov VM).

The disadvantages of the method for determining the flow rate of the coolant and the estimation of the measurement error are as follows. Replacing direct measurements of _DHW M with indirect measurements is mathematically equivalent, but not metrologically equivalent. The determination of the mass of the coolant selected from the heat supply system by the difference of the measured values of M ₁ and M ₂ can lead to a sufficiently large methodological error in determining the mass of the coolant selected from the heat supply system.

The objective of the present invention is to increase the productivity and accuracy of the calibration of pairs of identical volumetric flow meters for heat meters. The accuracy of the calibration of pairs of volumetric flow meters is increased by directly measuring the difference in the flow rate of the coolant in the supply and return pipelines, and along it the mass of the coolant selected from open water heat supply systems (OWST) and conditionally open water heat supply systems (UWST). The performance of the calibration device is increased due to the simultaneous calibration of a batch of pairs of volumetric flow meters for both the supply and return pipelines of open and conditionally open water heat supply systems.

The technical result is achieved by the fact that in a device for calibrating volumetric flow meters of a heat meter, comprising supply and return pipelines separated by a group of elbows or elongated by one line with volumetric flow meters connected in series, a block of bypass open and conditionally open wave heat supply systems containing one or more parallel branches of bypass pipelines, each of which is connected in parallel with the return pipe through controlled adjustable valves, and in Each branch of the bypass pipeline in series with at least two working reference volumetric flowmeters, controlled adjustable valves are connected, while the water enters the device from the return tank into the measuring channel of the supply pipe, to the input of which the working reference flowmeter unit is connected, and the water flows from the output of the return pipe into the initial standard of volumetric flow rate, consisting of a flow distributor and volumetric meters, moreover, all controlled and signal outputs of the volumetric flowmeter in and controlled gates are connected by indicator inputs.

и наибольшее

, где: L - искомое расстояние точки измерения до ближайшей градуировочной характеристики пары расходомеров по разности объемных расходов, L′ - оценка наименьшего из возможных значений L, L′′ - оценка наибольшего из возможных значений L, δ - среднее квадратичное отклонение.The technical result is also achieved by the method of calibrating volumetric flow meters of a heat meter, characterized by determining the flow rates in open and conditionally open water heat supply systems, reproducing by passing the coolant in the supply, return and bypass pipelines, determining the conversion coefficient of the tested volume flow meters and registering in the indicator, according to the invention, according to indications reference volumetric flow meters set the volumetric flow rate in the supply pipe, as indicated m of standard flow meters in bypass pipelines specify discrete values of the difference in volumetric flow rates in the supply and return pipelines equal to zero or more, and determine the identity and linearity of the characteristics of the calibrated pairs of volumetric flow meters, each flow meter is calibrated individually and in pairs, according to the readings of the flow meters of the reference and bypass blocks determine the flow rate in the supply pipe and the difference in volumetric flow rates in the supply and return pipelines and build a family of calibration characteristics to direct measurement of the difference in flow in rectangular coordinates, increase the accuracy of measuring volumetric flow by calibrating a pair of volumetric flow meters with linear calibration characteristics and direct measurement of the difference in flow rate in the supply and return pipelines on the value of the realized difference in volumetric flow rate of the coolant, while simultaneously determining the dependence of volumetric flow rate in the flow and return pipelines from the output signals (voltage) of the flow meters, then direct measurement of the different the cost of the directly reproduced value of this difference in costs with the minimum specified error and averaging time for the mth number of output voltages of the volumetric flow meters, build the dependence of the output voltage of the flow meter of the flow pipe from the output voltage of the flow meter of the return pipe at predetermined errors of the reproduced flow differences, measurement of the difference in volume flow with high accuracy and graphically display the smallest onset of error

and the greatest

, where: L is the required distance of the measuring point to the nearest calibration characteristic of the pair of flowmeters according to the difference in volumetric flow rates, L ′ is the estimate of the smallest possible value of L, L ′ ′ is the estimate of the largest of the possible values of L, δ is the standard deviation.

On figa shows a block diagram of a device for calibration (verification) of pairs of volumetric flow meters for heat meters and its individual nodes, figb. Figure 2 - 5 shows the calibration characteristics of the channel for direct measurement of the difference in the flow rate of a pair of flow meters obtained using the proposed device, and the assessment of the limits that arise with such a calibration, which constitute the error of the channel for the direct measurement of the difference in flow rate. The flowchart of the calibration device for flowmeters contains pipelines: supply (direct) 1, return 2, bypass unit 3, consisting of measuring pipelines 6. Pipelines 1 and 2 can be divided by a group of elbows 4 or extended in one line. The block of pipelines 3 is connected or separated from the return pipe by two adjustable shut-off valves 16-17. These valves are fully open or closed for the passage of water, i.e. the presence or absence of water flow in the bypass piping unit is ensured. Pipelines 1 and 2 (or channels 1 and 2) OVST or UOVST contain in each channel graduated volumetric flow meters 8-9, 10-11 from one or more pieces each. Combinations of pairs of volumetric flow meters are as follows: 8 and 10, 9 and 11, etc. At the outlet of the pipeline 2, a controlled flow control valve 12 is connected, with the help of which the coarse water supply to the block 3 is regulated from zero to the highest value (water or coolant flow rates).

At the output of the revolving tank 3, a first reference block 22 of FIG. 1b is connected with volumetric flowmeters 25-28, similar in design to the block of reference flowmeters 13, 14, 13 ′, 14 ′ on the bypass block 3. The reference block 22 serves for individual in-line graduation of each a flowmeter consisting of pairs of volumetric flowmeters 8-11 in channels 1, 2 according to reference flowmeters 25-28. To ensure adjustment of the water supply to block 22, high-precision adjustable controlled valves 29 m 30 are connected in series with flowmeters in each branch. The number of parallel branches in blocks 3 and 22 depends on the problem being solved.

The largest number of graduated flow meters on each of the branches 1 and 2 depends on the size of the device and the occupied workplace by each flow meter, taking into account the required lengths of straight sections.

When valve 12 is fully closed and valves 16-17 are open, water, bypassing channel 2, enters block 3, which contains reference volumetric flow meters 13, 14, 13 ′, 14 ′ and high-precision adjustable controlled valves 15, 15 ′. Block 3 is constructed similarly to block 22. Therefore, it is possible to calibrate the reference flow meters of blocks 3 and 22 according to the initial flow standard (hereinafter, the original standard) 31. Such an approach to the calibration of standard volumetric flowmeters increases the speed of their calibration by a factor of two.

In the process of calibration 13, 14, 13 ′, 14 ′ and 25-28, water through the l12 pipeline can enter the standard unit 31, either into the measuring unit 7 or 20, or through 17 or l20 to the circulating vessel 5. The standard unit 31 contains a flow distributor 18, which, depending on the flow rate, directs water (via pipelines l18 or l21) to a measuring device 7 or 20 of an appropriate volume, into which, when a measurement command is issued, the flow is directed by the corresponding flow switch 19, 21. For a predetermined time, water will flow into the measuring device, and then when giving a command at the end of the measurement, switch The transmitter will direct the flow through pipelines l7 or l20 to the circulating tank 5.

In standard 31, instead of measuring tanks 7, 20, reservoirs can be used in which the mass of incoming water is determined using weights.

From the return tank 5, water enters the measuring channel 6 through the pipe 24 using the pumping unit (or pump) 23. Thus, the calibration cycle of the flow meters by direct measurement of the difference in flow rates in the supply and return pipelines to the OVST and UOVST ends. The number of repetitions of these cycles is not limited, but to eliminate gross blunders of at least three. Repeated experiment repeats the accuracy of the calibration of flowmeters.

All technological processes - water supply, regulation of output voltage levels of flowmeters, open and closed position of controlled valves, controlled adjustable flow valves are controlled by indicator 32. The measurement results are processed in the indicator and a passport or form sheet is issued for each pair of flow meters.

On figa shows a block diagram of a device for calibrating pairs of volumetric flow meters by reproducing the most important working conditions of the flow meters in an open or conditionally open water heating system. According to GOST 26691 in open water heat supply systems, water is partially or completely taken from the network by consumers. A typical example of open water heat supply systems (OVST) is the presence of heat transfer for hot water supply in residential, public and industrial buildings.

If the selection of the coolant is unauthorized, then the OVST is usually called a conditionally open water heat supply system (UOVST). A sign (UOVST) are, for example, elements of heating systems where there are taps to remove air congestion that impede normal heat supply. Through these taps, the coolant may not be authorized to be removed. It is known that in real heat supply systems, the selection of coolant is possible both through standard elements (taps, hydrants, etc.), and through random formations (fistulas in pipelines, equipment malfunctions, etc.) and a flow meter installed on the hot water supply pipeline , does not give complete information about the amount of coolant selected from the heat supply system. The total amount of coolant taken from the OVST or UOVST for the reporting period can only be determined by the difference in the readings of the flow meters installed at the inlet to the supply and at the outlet of the return pipelines. However, the error of indirect measurement of the difference in mass of the coolant from the difference in the readings of the flowmeters will be large even if the errors of both flowmeters are within acceptable limits.

It is taken into account that the mass of the coolant is determined by multiplying the volume of the coolant by its density, which is determined by the measured values of pressure and / or temperature and GSSSD 188-99. The coolant volume is determined by integration over time of the volumetric flow rate (i.e. flow meter readings). In addition, the dependence of the density of the heating water (heat carrier) on its pressure in the heat supply system is usually neglected.

To significantly reduce the error of indirect measurement of the difference in mass of the coolant passing through the supply and return pipelines, it is advisable to use heat meters with direct measurement of the difference in flow rate of the coolant in the supply and return pipelines. However, in existing devices for calibrating flowmeters, the reproducible and measurable quantity is the flow of coolant (water). There are no devices for carrying out in-line graduation of pairs of flow meters according to the difference in flow rates in two pipelines. This disadvantage is eliminated in the proposed device using the bypass piping unit by accurately (0.15-0.3%) reproducing and measuring a predetermined amount of the heat carrier selected from the network existing in a real water heating system, including through a hot water supply (DHW) pipe.

A distinctive feature of the proposed calibration device is the determination of the metrological characteristics of volumetric flow meters for heat meters in pairs from the reproduced difference in volumetric flows using the bypass piping unit 3 connected to the return pipe 3 with flow meters 13, 14 and 13 ′ and 14 and control valves 15 and 15 ′, except Moreover, the presence of flow control valve 12 in pipeline 2. Using valves 12, 15 from return pipe 2, part of the pipelines open in the bypass unit is warm the carrier can be skipped bypassing the flow meters 10, 11. Thus, for the pairs of flow meters 8 and 10, 9 and 11, the required value of the difference in flow rates of the coolant, measured using the flow meters 13, 14 and 13 ′, 14 ′. The output signals (voltages) of the calibrated (verified) pairs of flow meters 8 and 10, 9 and 11, etc., are mapped to this precisely measured value of the difference in flow rates in pipelines 1, 2.

With fully closed valve 12 and open valves 16, 17, the flow meters of block 3 (simultaneously with the flow meters of block 22) are pre-calibrated according to the original standard 31. The limits of the permissible relative error of the standard volumetric flow meters 13, 14 and 13 ′, 14 ′ during single measurements should be are negligible in comparison with the permissible limits of the relative error of the graduated volumetric flowmeters 8, 11. The ratio of the errors of the standard flowmeters 13, 14 and 13 ′, 14 ′ and verified flowmeters 8-11 should not be less than her 1: 3. The calibrated flowmeters and reference flowmeters of unit 22 should have the same error ratio. The presence of two or more consecutively installed reference flowmeters on each of the reference lines of blocks 3 and 22 increases the accuracy and reliability of measurements; availability is regulated by GOST R 8.608.

, (где d - внутренний диаметр трубопровода), которая измеряется с помощью электродов. Выражение для е можно представить как:

, где Q - средний расход жидкости в мл/с. Питание расходомера осуществляют переменным или постоянным напряжением. Питание переменным напряжением устраняет электролитическую поляризацию расходомера, если частота достаточно высокая, а также позволяет использовать усилитель переменного тока (индикатор 32 содержит эти усилители) для усиления выходного сигнала расходомера. Выходное напряжение расходомера не зависит от характера потока - ламинарный или турбулентный и от профиля скорости потока, если он близок к осесимметричному. Однако значимая осевая несимметрия профиля скоростей потока может влиять на показания расходомера, поэтому перед расходомерами применяют прямые участки трубопроводов, на которых профиль скоростей стабилизируется.In the device, reference and checked (graduated) flowmeters are direct-acting flow rates with an induction system, since only such flowmeters provide the calibration curve that is closest to linear (P 50.2.026 - 2002 Resistance thermoconverters and electromagnetic flow meters in commercial heat metering units). The coolant flows through the flow part of the flow meter located in a magnetic field, the induction of which is B. Then in a liquid whose electrical conductivity should be in the range of 10 ^-3 -10 S / m (which is performed, including for heating water, an electric charge is induced and potential difference

, (where d is the inner diameter of the pipeline), which is measured using electrodes. The expression for e can be represented as:

where Q is the average fluid flow rate in ml / s. The flowmeter is supplied with alternating or constant voltage. AC voltage eliminates the electrolytic polarization of the flow meter if the frequency is high enough, and also allows you to use an AC amplifier (indicator 32 contains these amplifiers) to amplify the output signal of the flow meter. The output voltage of the flow meter does not depend on the nature of the flow — laminar or turbulent, and on the flow velocity profile, if it is close to axisymmetric. However, significant axial asymmetry of the flow velocity profile can affect the flowmeter readings, therefore, direct sections of pipelines are used in front of the flowmeters, on which the velocity profile is stabilized.

Errors in measuring the volumetric flow rate of the coolant can occur due to stray voltage between the electrodes of the flow meter. These voltages appear due to galvanic potentials between the electrodes and other metal parts, as well as when the flowmeter is polarized with DC voltage. The magnitude of random noise arising in the flow meter, and the influence of external electromagnetic fields increases with increasing resistance of the coolant.

The best results when calibrating (calibrating) pairs of electromagnetic flow meters by the difference in flow rates can be achieved for heat meters that are out of production with proven technology and high-quality assembly, for example, heat meters of the KM-5 type.

In the device, valves 16-17 are controllable ball valves that allow you to fully open or stop the flow of water. Controlled adjustable valves 15, 15 ′ with feedback allow you to adjust the flow of water in the pipelines based on readings 13, 14, 13 ′, 14 ′. All valves are standard, commercially available industry.

Tanks 7, 20 are measuring devices of the second category according to GOST 8.400, if the volume of the liquid is determined, or simple tanks with an anticorrosive coating, they must ensure complete drainage of the liquid after the measurement is performed, including the minimum adhesion of the liquid on the inner surface.

The principle of operation of the flowmeters of the calibration device is based on the phenomenon of electromagnetic induction, when the electrically conductive liquid passes through block 22, the reference flowmeters 25-28, adjustable controlled valves 29, 30 and a magnetic field with induction B induce an emf in the flowmeters The recorded signals from the outputs of the reference and graduated volumetric flowmeters are proportional to the induction of magnetic field B, the average flow rate of the fluid flow and the polarization voltage of the volumetric flowmeters.

The method of calibration of volumetric flow meters for heat meters OVST and UOVST is as follows.

They take advantage of the fact that at present, heat meters, which are measuring systems of the type IS-1 according to GOST R 8.596, are used to measure thermal energy and mass of the heat carrier selected from OVST and UOVST. The algorithm for calculating the thermal energy Q and the mass of the coolant selected from the heat network ΔM is based on the direct implementation of the measurement equations for these quantities given in MI. 2412-97 GSOEI “Water heat supply systems. The equations of measurements of thermal energy and heat carrier "and having respectively the form

; где m_i - массовый, q_i - объемный расход; ρ_i=ρ_i(P_i, t_i) - плотность, а h_i=h_i(Р_i, t_i) - энтальпия теплоносителя как функция давления Р_i и температуры t_i в измерительном сечении i-ого трубопровода вычисляют по ГСССД 188-99 Вода. Удельный объем и энтальпия при температуре 0...1000°С и давлениях 0,001...1000 МПа. Таблицы справочных данных (ГСССД, Госстандарт, М.: изд-во Стандартов, 1999. Нижние индексы у величин расхода, плотности, температуры, давления и энтальпии соответствуют: i=1 подающему, а i=2 обратному трубопроводам; h_ХВ - энтальпия холодной (подпиточной) воды (теплоносителя); τ - время, изменяющееся в интервале от τ₀ - начало, τ₁ - окончание отчетного периода.

; where m _i - mass, q _i - volumetric flow rate; ρ _i = ρ _i (P _i , t _i ) is the density, and h _i = h _i (P _i , t _i ) is the coolant enthalpy as a function of pressure P _i and temperature t _i in the measuring section of the i-th pipeline calculated according to GSSD 188-99 Water. Specific volume and enthalpy at a temperature of 0 ... 1000 ° C and pressures of 0.001 ... 1000 MPa. Reference data tables (GSSSD, Gosstandart, M .: Publishing House of Standards, 1999. The subscripts for the values of flow, density, temperature, pressure and enthalpy correspond to: i = 1 supply and i = 2 return piping; h _ХV - cold enthalpy (make-up) water (coolant); τ is the time that varies in the interval from τ ₀ is the beginning, τ ₁ is the end of the reporting period.

Stage 1. Set the zero difference in volumetric flow rates in the supply and return pipelines 1, 2, i.e. Δq = 0. This is achieved by the equality of volumetric costs in pipelines, i.e. q ₁ = q ₂ , while closing the valves 16, 17. And if the characteristics of the graduated pair of flowmeters are identical, then as a calibration characteristic at Δq = 0, an ideal straight line passing symmetrically to the coordinate axes is obtained, Fig.2. In addition, with closed valves 16, 17, flow meters 8-11 are individually and in pairs calibrated. Figure 3 shows that the actual calibration characteristic at Δq = 0 may not coincide with the ideal, but is in the tolerance field. Further, depending on the problem to be solved, the calibration of the pairs of flowmeters is carried out at several selected values of the difference in flow rates in pipelines 1 and 2 Δq ≠ Δq ₁ ≠ ... ≠ Δq _n and non-zero. In this case, the dependences of the output signals (voltage) of the pair of volumetric flow meters U ₁ , U ₂ are also built for each other at specified values of the difference in volumetric flow rates. The resulting family of lines, figure 4, is recorded in the heat meter indicator. During calibration, for given values of Δq _j , operations do not subtract volume flow rates in the supply and return pipelines. The flow values q ₁ in the supply pipe 1 and the flow difference Δq _j in the pipelines 1 and 2 are set according to the readings of the reference flow meters of units 3 and 22. For this, with the help of an adjustable controlled flow valve 12, a flow rate which is slightly larger than the required difference value is supplied to the bypass unit flow Δq _j in pipelines 1 and 2. Then, using the valves 15, 15 ′ according to the flow meters 13, 14, 13 ′ 14 ′, this value is adjusted, bringing it as close as possible to the required value Δq _j .

2 stage. Achieve high accuracy of measuring the difference in volumetric flow rates (0.15-0.3%) by introducing a direct reproduction of the value of the difference in flow rates in two pipelines, measured with high accuracy, for calibration (verification) of a pair of volumetric flow meters introduced into the heat meter of the measuring channel for direct measurement of the difference in volumetric flow rates of the coolant, figa.

The channel for direct measurement of the difference in flow rates is a complex measuring channel according to GOST R 8.596, the inputs of which supply output electrical signals from flowmeters in the supply and return pipelines. When determining the magnitude of the difference in volumetric flow rates in two pipelines using a direct channel for measuring the difference in flow rates, the operation of subtracting the costs measured by flowmeters, which is the source of a large methodological error, is not used.

3 stage. A pair of volumetric flowmeters of the measuring channel of direct measurement of the difference in flow rates is calibrated (verified) directly by the value of the flow difference reproduced with a predetermined small error. For this, at a given value Δq _j , the flow rate in the supply pipe is changed, and for the i point of change this value will be equal to q _1i , and the conversion coefficients of the pair of volumetric flow meters S _i = S _i (U ₁ , U ₂ ), where U _1i and U _2i is the output voltage of the graduated volumetric flow meters at the i - point. Next, an approximation is made of the values of S _{i of the} straight line, which will be the calibration characteristic of the channel for direct measurement of the difference in flow rates with the value Δq _j . All values shown in FIGS. 2-5 are given to the upper limit of measurements.

4th stage. The calibration characteristic of the pair of volumetric flow meters of the direct flow difference measurement channel is obtained as follows:

- Install flow meters on the supply and return pipelines of the calibration (measuring) section of the device, while observing the requirement for the choice of the length of the straight sections of the pipelines defined for this type of flow meter;

- At the installation, m values of the difference in flow rates in the supply and return pipes Δq _j where j are from 0 to m-1, where Δq ₀ = 0 (the number of m values and their distribution in the measurement range are selected depending on the specific requirements for measurement accuracy in problem being solved);

- For each of m, the Δq _j value sets n values of the flow rate in the supply pipe q _1i , where i is from 1 to n (the number of n values and their distribution in the measurement range are selected depending on the specific requirements for measurement accuracy in the problem to be solved);

- For each given pair of values of Δq _j and q _1i values, a pair of flow meters (total m × n values) is spilled and the output electrical signals of the flow meters U ₁ - on the supply pipe, U ₂ - on the return pipelines, Δq _j values measured with the specified error of 0.15-0.3%.

By selecting a pair of flow meters, a high accuracy of calibration of flow meters with a linear calibration characteristic is achieved (this requirement is most met by electromagnetic flow meters, which is confirmed by P 50.2.026-2002).

5 stage. The points obtained as a result of pouring are approximated, and the calibration characteristics of the channel for direct measurement of the difference in flow rates are presented as a family of straight lines, in rectangular coordinates, along the axes of which the output signals of the flow meters U ₁ , U ₂ are plotted (Fig. 4).

6 stage. The error of each straight line from the family of calibration characteristics of the direct flow difference measurement channel is determined as the sum of the device errors (0.15-0.3%) and the approximation errors of the calibration points obtained when the flow rate changes in the supply pipe at Δq _j = const. The approximation error is reduced by increasing the number of flow measurement points in the supply pipe.

7th stage. The total error of the channel for direct measurement of the difference in volumetric flow rates is determined from the sum of the errors of each flow meter (highlighted by dashed lines in Fig. 4) and the interpolation errors. Moreover, the interpolation error is reduced by increasing the number of calibration lines. Thus, it is shown that the error of the channel for direct measurement of the difference in costs does not depend on the measured difference in costs, and it is optimized at the calibration stage.

8 stage. The calibration errors of the direct flow difference measurement channel are determined as:

- Choose graduated volumetric flow meters of the same type from the same manufacturing group.

- Specify the limits of permissible relative errors for each flowmeter ± δ, in this interval an arbitrary law of variation of the error in time is allowed. It is assumed that the calibration characteristics of both flowmeters are linear within the permissible errors. Neglect the error of the applied standard measuring instruments.

- Make a graphical interpolation and on the coordinate axes postpone the output and signals of the flow meters: U ₁ located on the supply pipe, and U ₂ on the return - Figs. 4, 5.

9th stage. Idealize the calibration characteristic of the flow meter with the valve 12 closed, i.e. in the absence of a difference in flow rates (i.e., the mathematical expectation of the calibration characteristic is considered), and represent a straight line passing through the origin at an angle of 45 ° to both axes of Figures 4, 5, that is, the output voltages of the two flowmeters U ₁ and U ₂ are the same (Fig. 4, 5).

. Подробную градуировку в одной точке представляют на фиг.3. Реальную градуировочную характеристику располагают внутри данной полосы (пунктирная линия), где она может изменять свое местоположение.10 stage. The errors of the flow meters are taken into account, their readings are changed within the permissible limits, at each measurement point. The tolerance zone is limited by a square with side 2 | δ | (figure 2). And in the entire range of flow measurements, the tolerance zone is represented by a strip bounded by lines spaced from the mathematical expectation at distances

. A detailed graduation at one point is presented in FIG. 3. The actual calibration characteristic is placed inside this strip (dashed line), where it can change its location.

Similarly, the mathematical expectation of the calibration characteristics for other values of the differences of the costs (figure 4). They represent a family of lines having the equations U ₁ = U ₂ -ΔU, where ΔU is the value of the output signal of the graduated flow meter corresponding to the value of the difference in costs.

11 stage. Evaluate (determine) the limits of errors that occur during measurements.

, а наибольшее

. Таким образом, например, при δ=1% пределы погрешности измерений разности расходов составят ±2,8%.Get the desired value of the difference in costs for the measured values of the output signals (voltages) of the flow meters U ₁ ⁰ and U ₂ ⁰ , shown on the graph (figure 4), and at the intersection of the straight lines U ₁ = U ₁ ⁰ and U ₂ = U ₂ ⁰ and the lines Δq _j = const closest to it by linear interpolation determine the desired value Δq between the two lines Δq = const closest to the measuring point. In an enlarged form, this operation is shown in (figure 5). It is seen that Δq = Δq ₁ + L≡Δq ₂ -1, where L and 1 are the distances of the point (U ₁ = U ₁ ⁰ and U ₂ = U ₂ ⁰ ) to the nearest calibration characteristics. Figure 5 also give an assessment of the limits of the values of the error in determining the difference in costs. These limits are obtained by adding up the errors in determining the calibration characteristic (the band of its change is shown by dashed lines) and the errors of the flow meters (the bands of their change are shown by dash-dotted lines). The graph shows that the smallest value of this error is

and the largest

. Thus, for example, with δ = 1%, the margin of error for measuring the difference in costs will be ± 2.8%.

An analysis of errors shows an assessment of the limits of possible values, errors with a simultaneous combination of the most unfavorable factors. The calibration work on the proposed device determines the actual values of the errors of measurement of the difference in flow for specific pairs of flow meters.

Thus, the proposed method for calibrating flow meters allows you to:

- Remove the restriction on the nature of the error distribution for both flowmeters. Within the allowable interval, the variation in the errors of both flowmeters is allowed to be arbitrary, which is especially important in the presence of various conditions when calibrating the flowmeters at the installation and their application on a real object.

- Eliminate the largest error in the method of measuring thermal energy and mass of the heat carrier taken from the network by refusing to measure the difference in mass in the supply and return pipelines by the difference in the readings of the flow meters installed on these pipelines.

- Calibration or verification of a pair of flowmeters can be carried out by the flow method on a device where they reproduce the difference in the flow rate of the coolant with a minimum normalized error and observe the required ratio of errors for standard and graduated (verified) measuring instruments.

The technical and economic effect in the present invention increases due to the introduction of a direct metering of the flow rate difference in the heat meter, increasing accuracy by directly measuring the flow rate difference in open water heat supply systems using a pair of volume electromagnetic flowmeters installed in the supply and return pipelines without using the operation of subtracting the flow rates . Thus, they solve the tasks, i.e. increase the accuracy of measurements of heat energy and mass of the heat carrier taken from the network in open and conditionally open water heat supply systems, while maintaining the possibility of in-line graduation (verification) of pairs of heat meter flow meters, which compares favorably with the selected prototype and analog.

In LLC “TBN Energoservice” the analysis of the error limits of the calibration of channels for direct measurement of the difference in the flow rate of heat meters using the proposed device and method.

Improving the accuracy of mass measurements of the heat carrier taken from the network, obtained as a result of the proposed method for calibrating a pair of flow meters on the proposed device, is most clearly shown when assessing the marginal errors of measurement results that actually arise in practice.

Let the readings of the flowmeters be M ₁ and M ₂ , and the values of their relative errors during measurements will be δ ₁ and δ ₂ . It is required to find the measurement error of the difference ΔM = M ₁ -M ₂ .

The absolute errors of the measured quantities M ₁ and M _{2 are} determined as

Δ ₁ = M ₁ δ ₁ and Δ ₂ = M ₂ δ ₂ .

The measured values of the mass of the coolant, taking into account the error of the pair of flow meters, is defined as M ₁ + Δ ₁ = M ₁ + δ ₁ M ₁ and M ₂ + Δ ₂ = M ₂ + δ ₂ M ₂ .

The absolute measurement error of the difference in mass ΔM by definition is

Δ _ΔM = (M ₁ + δ ₁ M ₁ -M ₂ -δ ₂ M ₂ ) - (M ₁ -M ₂ ).

,Then the relative measurement error of the mass difference ΔM is written as

,

.after bringing such members get finally

.

It should be noted that formula (δ) is valid for the difference in the values of any physical quantities (temperatures, pressures, flow rates, etc.). In relation to the measurement of the difference in mass of the coolant in the supply and return pipelines, this formula is given in the regulatory document MI 2553-99.

To illustrate the application of the formula for determining the error 5, a number of practical examples are considered in the calibration device for a pair of volumetric flowmeters, in which the relative error of the measurement of the mass of the conditionally selected from the coolant network is determined.

For simplicity, in the examples below, only the error of the flow meters is taken into account. In practice, this is achieved by the fact that in heat meters the readings of temperature sensors - thermocouples of platinum resistance are imitated using high-precision resistors. The resistances of the reference resistances are selected in accordance with GOST 6651 so that the temperature in the supply pipe is simulated t ₁ = 120 ° C and in the opposite t ₂ = 70 ° C (at such temperatures, indicative calculations are performed for Moscow heating networks). The source data is selected from specific practical situations.

The limits of permissible relative error of both flow meters in the composition of the heat meter are chosen ± 1%. (Therefore, the same limits will be the error limits of the mass measurements for each pipeline).

The measured values of the mass of the coolant are set: on the supply pipe M ₁ = 100 tons, on the return M ₂ = 90 tons

but. A pair of flow meters is not consistent. The actual values of the errors of the flow meters obtained on the calibration device are δ ₁ = -0.6% and δ ₂ = + 0.3%, substitute them in the formula for δ and get

b. A pair of flow meters is consistent. The actual values of the errors of the flowmeters on the calibration device are estimated, the absolute value is obtained the same as in example a, but their signs will be the same, negative, i.e. δ ₁ = -0.6% and δ ₂ = -0.3%. Then by b get

It can be seen that matching flowmeters according to metrological characteristics gives a tangible increase in the accuracy of measurements.

at. A pair of matched flow meters is selected, and the values of their errors, as in example b, will be δ ₁ = -0.6% and δ ₂ = -0.3%, the measured mass values will be M ₁ = 100 t and M ₂ = 99 t, then

d. The greatest error for an inconsistent pair of flow meters (whose errors remain within the acceptable range) is obtained when δ ₁ = -1.0% and δ ₂ = + 1.0%, then for the measured masses M ₁ = 100 t and M ₂ = 99 t, the error mass difference measurements will be

It can be seen from case (c) that matching flowmeters according to metrological characteristics while reducing the difference in flow rates in the supply and return pipelines in situations most frequently encountered in practice does not give any effect and in extreme cases this error can have unacceptably high values.

Thus, it can be seen from the above examples that the main source of measurement error of the mass difference is the application of the method of measuring the mass difference by the difference in the readings of the flow meters. The error in measuring the mass difference caused by the application of the proposed method for calibrating volumetric flowmeters is unacceptably high, even if the errors in the flowmeters are within acceptable limits and are consistent in sign.

Analysis of the error formula allows us to draw the following conclusions:

If enough heat is taken from the water heat supply system (10% or more, which is rare in practice), the error signs of both measuring instruments coincide, then the error of the difference decreases, so in some cases it is advisable to select the measuring instruments in a matched pair. Moreover, the errors of both measuring instruments should be systematic and maintain stability over time (which is very problematic in practice).

The decrease in the measured value M ₁ -M ₂ leads to an increase in the error of its measurements, regardless of the values and signs of the errors of both measuring instruments. In this case, it is possible to increase the accuracy of volumetric difference measurement only by refusing to use the indirect method of measuring the difference and moving on to the invention of a method for directly measuring the desired difference M ₁ -M ₂ . To do this, it is necessary to use heat meters with a channel for direct measurement of the difference in flow rates in the supply and return pipelines.

To calibrate the pairs of flow meters for such heat meters should be on the proposed device by the proposed method.

Claims (2)

1. A method for calibrating volumetric flow meters of a heat meter, characterized by determining the flow rates in open and conditionally open water heat supply systems, reproducing by passing the coolant in the supply, return and bypass pipelines, determining the conversion coefficient of the volumetric flow meters to be verified and registering it in the indicator, in which, according to the indications of the reference volumetric flow meters set the volumetric flow rate in the supply pipe, according to the testimony of the standard volumetric flow meters for bypass pipes wires specify discrete values of the difference in volumetric flow rates in the supply and return pipelines, equal to zero or more, and determine the identity and linearity of the characteristics of the calibrated pairs of volumetric flowmeters, while each flowmeter is graduated individually and in pairs, according to the readings of flow meters of the reference and bypass blocks, the flow rate in the supply pipeline is determined and the difference in volume flow in the supply and return pipelines and build a family of calibration characteristics of the channel for direct measurement of the difference in flow in rectangular coordinates, increase the accuracy of volumetric flow measurements by calibrating a pair of volumetric flowmeters with linear calibration characteristics and direct measurement of the difference in volumetric flow rates in the supply and return pipelines on the value of the realized difference in volumetric flow rates of the coolant, while simultaneously determining the dependence of volumetric flow rates in the supply and return pipelines on the output signals (voltage) of the flow meters, then directly measure the difference in flow rates directly in the produced value of this flow difference with the minimum specified error and averaging time for the mth number of output voltages of the volumetric flowmeters, plot the output voltage of the flow meter of the supply pipe on the output voltage of the flow meter of the return pipe at predetermined errors of the reproduced flow differences, measure the difference in volumetric costs with the highest accuracy and graphically display the smallest possible error

and the largest value of the error

where L is the required distance of the measuring point to the nearest calibration characteristic of the pair of flow meters according to the difference in volumetric flow rates, L ′ is the estimate of the smallest possible value of L, L ′ ′ is the estimate of the largest possible value of L, δ is the standard deviation. 2. A device for calibrating volumetric flow meters of a heat meter, comprising supply and return pipelines separated by a group of elbows or elongated in one line with volumetric flow meters in series connected thereto, a block of bypass open and conditionally open water heating systems, containing one or more parallel branches of bypass pipelines, each of which is connected in parallel with the return pipe through controlled adjustable valves, and in each branch of the bypass pipe Consistently with at least two working reference volumetric flowmeters, controlled adjustable valves are connected, while the water enters the device from the return tank into the measuring channel of the supply pipe, to the input of which the unit of working reference flowmeters is connected, and from the output of the return pipe the water enters the original volumetric reference flow rate consisting of a flow distributor and volumetric meters, and all controlled and signal outputs of volumetric flowmeters and controlled valves are connected to the input E indicator.

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