1、Specification, Installation,and Calibration of Turbine FlowmetersApproved 30 April 1977ISARP31.11977RECOMMENDED PRACTICEISA The Instrumentation,Systems, andAutomation Society TMCopyright 1977 by the Instrument Society of America. All rights reserved. Printed in the UnitedStates of America. No part o
2、f this publication may be reproduced, stored in a retrieval system, ortransmitted in any form or by any means (electronic, mechanical, photocopying, recording, orotherwise), without the prior written permission of the publisher.ISA67 Alexander DriveP.O. Box 12277Research Triangle Park, North Carolin
3、a 27709ISARP31.11977, Specification, Installation, and Calibration of Turbine FlowmetersISBN 0-87664-371-3ISA-RP31.1-1977 3PrefaceThis preface is included for informational purposes and is not part of Recommended Practice ISA-RP31.1-1977.This Recommended Practice has been prepared as part of the ser
4、vice of ISA toward a goal of uniformity in the field of instrumentation. To be of real value, this document should not be static, but should be subject to periodic review. Toward this end, the Society welcomes all comments and criticisms, and asks that they be addressed to the Standards and Practice
5、s Board Secretary, ISA, 67 Alexander Drive, P.O. Box 12277, Research Triangle Park, NC 27709, telephone 919-549-8411, e-mail: standardsisa.org.The ISA Standards and Practices Department is aware of the growing need for attention to the metric system of units in general, and the International System
6、of Units (SI) in particular, in the preparation of instrumentation standards. The Department is further aware of the benefits to USA users of ISA standards of incorporating suitable references to the SI (and the metric system) in their business and professional dealings with other countries. Toward
7、this end, this Department will endeavor to introduce SI and SI-acceptable metric units as optional alternatives to English units in all new and revised standards to the greatest extent possible. The Standard for Metric Practice, which has been published by the American Society for Testing and Materi
8、als as ANSI-Z210.1 (ASTM E 380-76; IEEE 268-1975) and future revisions will be the reference guide for definitions, symbols, abbreviations, and conversion factors.The ISA Standards Committee on Turbine Flowmeters, SP31, operates within the ISA Standards and Practices Department, L. N. Combs, Vice-Pr
9、esident. The men listed below serve as members of this committee.NAME COMPANYM. J. Ford, Chairman Pratt the terms defined in 4.3 Specific Terminology appear in italics.4.1 Design characteristics4.1.1 The following mechanical design characteristics shall be specified.1) *Measured FluidsThe liquids to
10、 be in contact with the wetted parts, e.g., JP-4 fuel, hydrochloric acid,etc.2) Configuration and Dimensionsa) For flared tubing (MS 33656) the nominal tube size, overall length, and equivalent fittings.b) For flanged types the nominal pipe size, and length between flanges.c) For male pipe-threaded
11、flowmeters the nominal pipe size and overall length.3) Mountings and Mounting DimensionsUnless the process connection serves as a mounting, the outline drawing shall in-dicate the method of mounting with hole sizes, centers and other pertinent dimen-sions, including thread specifications for threade
12、d holes, if used.4) The weight of the flowmeter.5) The following information shall be permanently marked on the flowmeter housing.a) Manufacturerb) Part or Model No.c) Serial No.d) Flow Directione) Nominal Tube or Pipe SizeISA-RP31.1-1977 114.1.2 Supplemental mechanical design characteristicsThe fol
13、lowing mechanical design characteristics shall be specified at the option of the purchaser.1) Minimum and maximum temperaturesThe minimum and maximum temperatures of the measured liquid, and of the sur-rounding environment.2) PressureThe maximum pressure of the measured liquid.3) SpeedThe maximum ou
14、tput frequency which the flowmeter can produce without physicaldamage.4.1.3 Required electrical design characteristicsThe following electrical characteristics shall be specified.1) *Excitation (modulating type only). Expressed as “_volts at_hertz.“2) *Electrical outputa) Output voltageExpressed as “
15、_volts“ minimum peak-to-peak at any flow within the operatingrange.b) Frequency at maximum rated flow expressed as “_Hz.“4.2 Performance characteristicsThe pertinent performance characteristics of turbine flowmeters should be specified in the order shown. Unless otherwise stated, they apply at *Room
16、 Conditions, as defined in ISA-S37.1 and are expressed in SI units. (Equivalent units may be substituted.)4.2.1 *RangeExpressed as “_to_meter3per second.“ 4.2.2 Linear rangeExpressed as “_to_meter3per second.“4.2.3 *SensitivityThe sensitivity (K factor) is expressed as “_cycles per meter3.“ Often us
17、ed as K , which is the average sensitivity across the flow range of interest to the user. Average is used here in the sense of (Kmax + Kmin)/2.4.2.4 *LinearityThe normal presentation of the calibration data is in cycles per meter3vs. frequency, which is the slope of a curve of flow vs. frequency. Li
18、nearity is then expressed as “_% of the average sensitivity (K factor).“ (See Linearity in 4.3 Specific Terminology.)12 ISA-RP31.1-19774.2.5 Pressure dropThe pressure drop across the flowmeter at maximum rated flow, expressed as “_differential pascals at _meter3per second“ when used with specific me
19、asured liquid.4.3 Specific terminologyActual flow: Refers to the actual volume of liquid passing through the flowmeter in a unit time as computed by applying all necessary corrections for the effects of temperature, pressure, air buoyancy, etc. to the corresponding readings indicated by the calibrat
20、or.Air buoyancy: The lifting effect or buoyancy of the ambient air which acts during a “weighing“ procedure with open gravimetric calibrations. This is caused by displacement of air from the measuring vessel during the calibration run. The standard air (50% R.H.) for correcting to “weights“ in vacuu
21、m has a density of 1.217 kg/m3at 288.7 K and 1.013 250E+05 Pa. When “weighings“ are made against “weights,“ the buoyancy force on these must also be considered. For brass “weights“ the net effect of air buoyancy in air at standard conditions is about 0.015%. Exact values can be determined by procedu
22、res outlined in paragraphs 3059 and 3060 of API Standard 1101, 1960 Editions, and NBS Handbook 77, Volume III, Pages 671-682.Apparent flow: The uncorrected volume flow as indicated by the calibrator.Back pressure: The absolute pressure level as measured four pipe-diameters downstream from the turbin
23、e flowmeter under operating conditions, expressed in pascals.*Calibration curve: A graph of the performance of a turbine flowmeter, showing sensitivity as the ordinate and volume flow, flowmeter frequency, or frequency divided by kinematic viscosity as the abscissa, for a liquid of specified density
24、, viscosity, and temperature.Calibration system: A complete system consisting of liquid storage, pumps, and filters; flow, pressure, and temperature controls; the quantity measuring apparatus; and the associated electronic instruments used to calibrate turbine flowmeters.Correlation check: A procedu
25、re whereby the performance and accuracy of a calibration system is checked against another calibration system using “Master Flowmeters“ as the standards.Density: The mass of a unit volume of a liquid at a specified temperature. The units shall be stated, such as kilograms per meter3. The form of exp
26、ression shall be: Density _kg/m3at _Kelvin.Dynamic calibration: A calibration procedure in which the quantity of liquid is measured while liquid is flowing into or out of the measuring vessel.Flow: the rate of flow of a liquid expressed in volume units per unit of time. Examples are: meter3/second (
27、m3/s).Flow straightener: A supplementary length of straight pipe or tube, containing straightening vanes or the equivalent, which is installed directly upstream of the turbine flowmeter for the purpose of eliminating swirl from the fluid entering the flowmeter.Gravimetric: A descriptive term used to
28、 designate an instrument or procedure in which gravitational forces are utilized. However, the results or indications of such procedures are not necessarily influenced by the magnitude of the acceleration of gravity. See discussion on mass, weight, and weighing (5.4.1 (1) Mass, Weight, and Weighing)
29、.Linear range of a turbine flowmeter: the flow range over which the output frequency is proportional to flow (constant K factor) within the limits of linearity specified.Linearity of a turbine flowmeter: the maximum percentage deviation from the average sensitivity (K) across the linear range.ISA-RP
30、31.1-1977 13Master flowmeter: Flowmeter used as an inter-laboratory standard in correlation checks of calibration systems.Measuring vessel: The container in which the liquid metered by the turbine flowmeter during calibration interval is collected and measured. In a direct-gravimetric calibration sy
31、stem, this is a tank on a weigh scale and the exact dimensions are not significant. In indirect-gravimetric systems and volumetric systems the cross-sectional area or actual volume, respectively, must be known to a precision compatible with the desired accuracy of calibration.Pressure drop: the diff
32、erential pressure in pascals at a maximum linear flow measured between points four pipe diameters upstream and four pipe diameters downstream from its ends, using a specified liquid, and using pipe size matching the fittings provided.The *sensitivity of a turbine flowmeter is designated by the lette
33、r “K“ and is expressed in cycles per meter3, under the following specified conditions:1) Calibration Liquida) Density (kg/m3)b) Viscosity (m2/s)c) Downstream Temperature (K)d) Back pressure (Pa abs)e) Flow (m3/s)2) Line Configurationa) Length of straight line upstreamb) Length of straight line downs
34、treamc) Configuration of flow straightenerReference flowmeter: Flowmeter used as a transfer standard for in-system and comparison calibrations of turbine flowmeters.Static calibration: A calibration procedure during which the quantity of liquid is measured while the liquid is not flowing into or out
35、 of the measuring vessel.Swirl: A qualitative term, describing tangential motions of liquid flow in a pipe or tube.Thermal expansion: The increase in a volume of liquid caused by an increase in temperature.Turbine, turbine supports(s), housing and transduction coils: the preferred names for the majo
36、r parts of a turbine flowmeter.Turbine flowmeter with an electrical output: a flow measuring device in which the action of the entire liquid stream turns a bladed turbine at a speed nominally proportional to the volume flow, and which generates or modulates an output signal at a frequency proportion
37、al to the turbine speed.Two-phase: A fluid state consisting of a mixture of liquid with gas or vapors.Vapor pressure: The pressure of a vapor corresponding to a given temperature at which the liquid and vapor are in equilibrium. Vapor pressure increases with temperature.Vapor pressure, Reid: The vap
38、or pressure of a liquid at 100F (311K) as determined by ASTM Designation D 323-58, “Standard Method of Test for Vapor Pressure of Petroleum Products (Reid Method).“14 ISA-RP31.1-1977Viscosity, absolute: The property by which a fluid in motion offers resistance to shear. Usually expressed as newton-s
39、econds/meter2.Viscosity, kinematic: The ratio of absolute viscosity to density. The SI unit is the meter2/s.Weigh-scale: A device for determining either the mass or the weight of a body depending upon the apparatus and procedure employed.Weighing: The process of determining either the mass or weight
40、 of a body depending upon the apparatus and the procedure employed.Weight: The force with which a body is attracted by gravity. The newton is the unit force in this Standard.Weights: Reference units of mass such as counterpoise “weights“ used with lever balances and dead “weights“ used in calibratin
41、g balances, scales, and pressure gauges.4.4 Tabulated characteristics vs. test requirementsThe table on the following page is intended for use as a quick reference for design and performance characteristics and tests of their proper verification as contained in this Standard.5 Individual acceptance
42、tests and calibrations5.1 Calibration methodsMethods suitable for the calibration of turbine flowmeters may be classified as:1) Gravimetric (direct or indirect)2) Volumetric3) ComparisonEach of these methods has advantages and disadvantages depending upon the liquid being metered and the type of ope
43、ration. The gravimetric methods require that the density of the liquid be determined accurately to provide a basis for converting mass to volume. The effect of the gas added to the “weigh“ tank in closed gravimetric calibrators must also be considered. The buoyancy factor for air, in open gravimetri
44、c calibrators, as a function of liquid density is shown in Figure 1. (See also 4.3 Definitions, air buoyancy.) The volumetric method is more direct in that conversions from mass to volume are not required.The calibrator may be of either the open-type for use with low vapor pressure liquids only, or
45、the closed-type in which a back pressure greater than atmospheric is maintained to prevent liquid loss from the measuring vessel by evaporation. Calibration methods are further classified as Static or Dynamic.ISA-RP31.1-1977 155.1.1 Static methodIn this method, “weighing“ or measurement of volume oc
46、curs only while the liquid is not flowing into or out of the measurement vessel. This method is capable of high accuracy under proper conditions and should include static checks against reference units of mass or volume traceable to the National Bureau of Standards.5.1.2 Dynamic methodIn this method
47、, the measurement of volume or mass occurs while the liquid is flowing into or out of the measuring vessel. Although more suitable for many applications, it may involve dynamic errors which cannot be detected through static checks with reference units of mass or volume. Therefore, it is important th
48、at each new dynamic calibrator of a different type or size be checked carefully by correlation or other suitable means to prove that significant dynamic errors do not exist.Two procedures for conducting a turbine flowmeter calibration are the running start-and-stop and the standing start-and-stop. T
49、he procedure which more closely duplicates the type of service anticipated in the application of the flowmeter should be selected whenever possible.5.1.3 Running start-and-stopThe running start-and-stop requires that a reasonably constant flow be maintained through the flowmeter prior to, during, and immediately after the collection of the liquid in the measuring vessel. This is accomplished by using a stream diverter, whose motion is synchronized with the starting and stopping of the electronic counter.Design Characteristic Verified DuringCharacteristics
