Measuring and testing – Instrument proving or calibrating – Volume of flow – speed of flow – volume rate of flow – or mass...
Reexamination Certificate
1999-09-20
2002-04-09
Raevis, Robert (Department: 2856)
Measuring and testing
Instrument proving or calibrating
Volume of flow, speed of flow, volume rate of flow, or mass...
Reexamination Certificate
active
06367306
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention is a reform method of an industrial meter to measure fluid to flow in a pipe with high precision.
The present invention relates to a compensating method and device for instrumental error in a rotary positive displacement flowmeter. The method and device of the invention are intended for compensation of errors due to flowmeter characteristics, correlation of temperatures, subject fluid volumetric expansion, correlation of temperatures and an inner leakage correlated viscosity vs. temperature of the fluid.
Elliptical gear type and roots rotor type flowmeters are outstandingly superior in measurement functions to other conventional flowmeters, and therefore most suitable for further enhancing measurement functions of the present invention in error compensation. Moreover, reliability of flowmeters are enhanced by the present invention.
A conventional positive displacement type flowmeter with only a calculation method to revise expansion of volume accompanied with a fluid temperature inflexion, showed amount of flow. A function to revise an influence that fluid viscosity changes by a temperature missed. It is defective not to show correct amount of flow.
A revision of a capacity type flowmeter is for a temperature and a correlative relation. Change of volume versus temperature and, a revision of viscosity inflexion vs. temperature are necessary. The inventive method revises fluid volume inflexion and inside omission simultaneously.
For the inventive method to revise metering error, there is a function to revise the error of a capacity type flowmeter and it makes up for a defect of mechanical structure of the flowmeter.
Fluids generally used in plant facilities have mostly low viscosity. Fluids of low viscosity have large viscosity variations with temperature, and therefore can not be exempt from errors even with high precision instruments. Since, in low viscosity fluid viscosity, variations can result with a small temperature change, and errors in accuracy will be inevitably produced, technology is needed in temperature control when a measurement is to be conducted in such cases. Generally, it is accepted that a non-circular gear flowmeter has high reliability. The relation between the flow rate and instrumental error will be unchanged, and therefore super precision measurement can be made possible by compensation methods using microcomputers. Because of mechanical structures in rotary positive displacement flowmeters, leakage of fluids due to pressure differences can not be perfectly prevented through even small clearances between rotors or the inside wall and rotors. This leakage rate varies with viscosity changes caused by temperature changes in subject fluids and apparatus error increases or decreases throughout the flow rate range.
The action of temperature compensation mechanisms for conventional positive displacement flowmeters is to make a real time determination of the fluid expansion and shrinkage and an inner leakage from metering chamber due to temperature rise and fall during the measurement for continuous conversion to volumes at certain conditions. However, the flowmeters do not indicate real correct flows because the fluid viscosity varies with the change in the fluid temperature.
SUMMARY OF THE INVENTION
An error is not exempted, even though a viscosity exponential low case considers that a viscosity inflexion depending on a temperature used a meter of a high precision, greatly for fluid that is generally used in a conventional technology plant. Temperature though need technology of an altitude in order to manage it precisely, an even scant temperature inflexion accompanies an inflexion of viscosity, and an error of a precision depending on this occurs.
It is desirable to rotate, as a gap with both ends of a mask of a rotation body keeping an equal certain price. It scantly makes one familiarize an inflexion of a metering error performance which is important for exemption that a rotation body is kept by a central position exactly. Quantity leaking from a very small gap accompanied with an inflexion of momentum inertia depending on rotation speed of a non-round rotation body for this reason is because movement of free horizontal direction is possible for a rotation body for a conventional horizontal axis type. A clearance of both ends is not kept accompanied with a fluid stream where a metering error changes it is a defect that the exact amount of flow display is not obtained immediately. Though an electric error revision microcomputer shows a precise calculation function, if a metering error revision performance will change by abrasion of a measuring rotor element of the meter main part, such a revision becomes meaningless.
Because a minimum clearance is kept, in the intervals with a measuring chamber wall and rotor body to add an engagement mutually to form a measuring function of roots rotation body, a freedom rotation is given, and a leakage from a gap can measure it with a minimum ratio. A leakage from this clearance is prohibited. Though a metering error gets a few, the danger of stopping increases, as biting a very small solid foreign substance. Consequently, where a gap in the metering chamber is necessary, a leakage occurs necessarily, and it is impossible to do a metering error for zero.
However, for a positive displacement type flowmeter as far as there is not wear of a rotor, it is possible to minimize this by an electric revision function.
In case the temperature is high, viscosity of clear water drops, and leakage increases from a gap.
Resistance of leaking from a gap increases it, because viscosity increases on the condition that a temperature is low. An omission quantity gets a few.
The coefficient of an inflexion showed −0.02%/° C., with Oval Flowmeter of 56 type, 50 mm dia. For 0F40S Flowmeter, 40 mm dia coefficient shows −0.03%/° C. by water test.
A coefficient of Mini-oil Meter, ⅛ inch dia. (3 mm dia.) shows −0.10%/° C.
Since clearance changes relatively by a caliber of meter, a difference of this coefficient, with a small model of a caliber, a ratio of a measuring gap gets relatively large.
For an oval type flowmeter of a small size, if a clearance gets small, though a precision goes up, there is a limit, because the danger of stopping gets comparatively large.
As a positive displacement type flowmeter is a mechanical structure, with a sequence of operation time, performance falls by an abrasion of a rotation element for a measuring function. A configuration is necessary for durability to be superb.
It is important in order to keep a measuring precision to be exactly maintained a measuring function of rotator elements.
By an electric system error revision equipment for a performance of a positive displacement type flowmeter can be raised.
In the case where a metering error characteristic is certain, it is possible to obtain zero error by electronic equipment as, it is possible to revise a fluid volume expansion and meter peculiar error.
Lubrication fluid does not damage the rotation body or the inside part of the measuring chamber. Consequently, an inside clearance of a flowmeter does not change. An amount of flow is displayed as correct flow rate by a rotation of a rotor.
The inventive task is to compensate a change of liquid volume by temperature, to compensate a change of inner leakage by change of temperature and to exempt a peculiar error of flowmeter. It is the purpose to give an exact amount of flow indication.
This inventive method is a method to exclude a meter peculiar error. Leakage from meshing part of elliptic gear rotors and a clearance between an inner side of measuring chamber changes in order to differ by a temperature condition. There as meter peculiar removing is necessary.
For a cause of an inflexion depending on a temperature condition of a positive displacement type flowmeter is an inner leakage form a clearance in metering chamber and a change of fluid volume by temperature condition.
A revision calculation is possible with a single ROM having factions of
Jacobson & Holman PLLC
Raevis Robert
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