RU2217705C2 - Method for metrological certification of flowrate metering systems - Google Patents

Abstract

FIELD: measuring processes and apparatuses. SUBSTANCE: method comprises steps of passing flow of working fluid with fixed value of flowrate through each of flowrate meters connected mutually in parallel; comparing readings of first flowrate meter with reference value for certifying desired flowrate meter; certifying remaining flowrate meters by replacement way while providing target flowrate of working fluid through each successive flowrate meter and reference meter according to readings of previously certified flowrate meters; in addition setting in last flowrate meter reference value and passing through it necessary flowrate of fluid; evaluating error of metrological certification of the whole system by comparing certification results of last flowrate meter in flowrate metering system and in reference system. EFFECT: enhanced authenticity of metrological certification.

Description

 The invention relates to measuring equipment and is intended for accurate measurement of the flow rate of various environments, certification of flowmeter installations, calibration and calibration of flowmeters.

 Known methods for calibrating flowmeter installations, such as critical nozzles, are based on measuring the amount (volume or mass) of gas flowing through a critical nozzle and the length of time during which this amount has passed. If time measurement is not a problem, then measuring the amount of gas due to its volatility and compressibility creates significant difficulties, especially with large volumes of gas (V.I. Gurov. On determining the flow coefficient of critical flow meters, Metrology, Publishing House Standard, 6, 1977) - [ 1, p. 48-52].

A known calibration method, referred to as a constant-volume method or PVT method (Watana be N. Komija K. The coefficient of flow rate of the critical Venturi nozzle. Metrology and measurement technology. Issue II, 1980, Abstract 739) - [2, p. 20- 25]. In this method, a known volume V pre-evacuated container, after temperature equalization inside and outside the vessel measured residual pressure P ₁ therein, then the critical nozzle and a shut-off valve interlocked with a stopwatch, the container filled with air from the atmosphere to a pressure P _2. The tank filling time τ is determined by the on-time of the shut-off valve. The pressure P ₂ should provide a critical flow regime, the value of which is also measured after equalization of the gas temperature in the filled tank. As a result, the volumetric flow rate Q through the nozzle is determined according to the expression Q = [(P ₂ -P ₁ ) / (P _a • τ)] • V, where P _a is the atmospheric pressure. The disadvantage of this method is the long calibration time associated with the need for temperature equalization. In addition, this method becomes economically impractical for calibrating large-diameter nozzles, because a large volume capacity is required when the high rigidity of its walls is required.

 One of the ways to increase the economic efficiency of the calibration and calibration of flowmeters is the introduction of verification methods by comparison with a working standard. In this case, the use of stationary expensive standards is assumed only as the initial means of transmitting the size of the unit of expenditure. Further, it is advisable to transfer the flow rate unit using steps increasing in flow rate, consisting of working reference flow meters installed in parallel, each of which is used only at one point near its upper measurement limit. As working reference flowmeters, commercially available devices specially certified for the corresponding stage can be used. Each subsequent step is certified with the help of the previous one, which can also be used to test working measuring instruments (B.V. Biryukov, M.A.Danilov, S.S.Kivilis. Accurate measurements of fluid flow. Reference manual. M., Engineering, 1977) - [3].

 The prototype of the invention is a method of metrological certification of flowmeter installations to a. from. 1657971, G 01 F 25/00, publ. BI 23 of June 23, 1991 - [4]. According to this method of metrological certification of flowmeter installations with a set of parallel-connected flowmeters, separate certification of each flowmeter of the set is carried out by passing through it a flow of the working medium at a fixed value of the flow, the readings of the first of the flowmeters are compared with the indications of an exemplary means (reference), receiving a certified flowmeter, the rest of the flowmeters of the set certified by the replacement method with the formation of the required flow rate of the working medium through each subsequent flow meter and device comparison according to the testimony of previous certified flowmeters.

A device that implements this method consists of a set of n certified flowmeters installed, as well as the corresponding n valves in parallel branches of the pipeline. A set of flowmeters is connected in series to a comparator, for example, a tachometric flow transducer, and through a tap to the original model tool. A medium is passed through the first flowmeter with a flow rate Q _max corresponding to the lower limit of the installation measurement, the readings of the flowmeter are compared with the standard means, and the conversion coefficient of this flow meter K ₁ is determined at a flow rate of Q = Q _min . Then, a flow meter is connected in series with the comparison device and the flow rate Q _{2 is set to} be close to or equal to Q = Q _min , the readings of the comparison device (Q ₂ ) and the second flow meter are taken simultaneously and the coefficient K _{2 is} determined. To certify the subsequent third flowmeter, both certified flowmeters are connected to the comparison device, the first and second, according to the known K ₁ and K _2, specify the flow and, with a total flow (Q ₁ + Q ₂ ), K _{3 is} determined. Thus certify all dial flow meters.

 This method allows to significantly expand the range of reproducing the flow rate of the certified installation without increasing the number of flow meters in the set, to use the original standard measuring instrument with a lower upper limit, to ensure its more efficient use due to the application for certification of the range-related installations and to reduce the costs associated with certification of installations.

 However, during the certification of each subsequent flow meter, the certification error increases and an incorrectness arises in the implementation of the method, which consists in the fact that the accuracy of the entire device for metrological certification of flow meter installations cannot be considered accurate for the first certified flow meter from the set of this device.

 The invention solves the problem of increasing the reliability of the metrological certification of flowmeter installations by determining the error of the method, thereby increasing the economic efficiency of practical applications.

 The problem is achieved in that according to the method of metrological certification of flowmeter installations with a set of parallel-connected flowmeters, based on the separate certification of each flowmeter of the set by passing through it a flow of the working medium at a fixed flow rate, according to which the readings of the first of the flowmeters are compared with the reference reading, getting certified flowmeter, the remaining flowmeters of the set are certified by the replacement method with the formation of the required flow rate of the working medium through each the following flowmeter and a comparison device according to the testimony of previous certified flowmeters, in addition, the last flowmeter is installed on the standard and the required medium flow rate is passed through it, receiving a certified flowmeter, the results of certification of this flowmeter on the standard and the certified flowmeter are compared, and the measurement result is judged on the error of the metrological certification of the whole flowmeter installation.

 The method is as follows.

When the corresponding valve and tap are open, the working medium is passed through the first flow meter with a flow rate of Q _min corresponding to the lower limit of the measurement of the installation, and through the initial standard (reference) means of measuring the flow rate and comparing the measured flow rate with the reading of the first flow meter, the conversion coefficient K _{1 of} this flow meter is determined at a flow rate of Q ₁ = Q _min .

Then, in series with the comparison device, a second flow meter is connected and a flow rate Q _{2 is established} , which is close to or equal to Q ₁ = Q _min , the readings of the comparison device and the second flow meter are taken simultaneously, the conversion coefficient K _{2 is} determined. To certify the third flowmeter, both certified flowmeters are connected to the comparison device, according to the known K ₁ and K _{2, the} flow is set and, with a total flow rate of Q ₁ + Q ₂ , K _{2 is} determined.

Кроме того, дополнительно последний расходомер устанавливают на эталон и пропускают через него необходимый расход среды, равный Q_э=Q_п. Сравнивают результаты аттестации этого расходомера на эталоне и на самой аттестуемой расходомерной установке и по результату сравнения судят о погрешности метрологической аттестации всей расходомерной установки.Thus, all flow meters of the set are certified, while for the last n-th flow meter, the flow rate is

In addition, in addition, the last flow meter is installed on the standard and the required flow rate of the medium equal to Q _e = Q _{p is} passed through it. The results of certification of this flowmeter on the standard and on the most certified flowmeter installation are compared and the measurement result of the metrological certification of the entire flowmeter installation is judged by the result of the comparison.

Claims (1)

A method of metrological certification of a flowmeter installation with a set of parallel-connected flowmeters, based on the separate certification of each flowmeter of the set by passing through it a flow of the working medium at a fixed value of the flow, by which the readings of the first of the flowmeters are compared with the reference reading, obtaining a certified flowmeter, the remaining flowmeters of the set are certified by the method substitution with the formation of the required flow rate of the working medium through each subsequent flow meter and comparison device according to Kazan previous certified flowmeters, characterized in that the last meter is mounted on the standard and passed through the required flow rate of the medium, getting certified meter, compared to the results of certification of the meter on the reference and attested flow installation and the comparison results are judged on the uncertainty of metrological certification of the installation flow.