US 5,331,838 AGranted

Dead weight piston drive and control system

OwnerPierre R. Delajoudinventor

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Abstract

An improved dead weight piston pressure measurement/calibration device includes a cylinder and a dead weight piston assembly that includes a piston rotatable and vertically in the cylinder, bell housing supported by the piston and carrying a number of calibration weights. The weight of the dead weight piston assembly initially is supported by an elastic stop device. Gas from an external source is rapidly forced into the cylinder until the dead weight piston assembly rises in an "elastic" zone defined by the elastic stop device. Such movement is sensed to "proportionally" reduce the rate of flow of gas and stabilize the position of the piston in the second element in a free-floating equilibrium condition, and actuate a drive mechanism that rotates the dead weight piston assembly and maintains the rotation rate in a defined range without producing any sustained vertical or radial displacement forces on the dead weight piston assembly, and thereby avoiding pressure overshoot.

Claims24

Dependent claims

A dead weight piston pressure measurement device, comprising in combination:

(a) a cylinder;
(b) a piston rotatable in the cylinder, and vertically moveable in the cylinder, the piston supporting a plurality of calibration weights and a cylindrical drive surface coaxial with the piston;
(c) an external fluid source coupled to supply a flow of fluid, the pressure of which is to be measured or calibrated, into or out of a volume between the cylinder and the piston to vertically move the piston in the cylinder, the combined weight of a dead weight piston assembly including the piston and the calibration weights accurately indicating the pressure of the fluid in the volume when the piston is in a free-floating equilibrium condition in the cylinder;
(d) a drive mechanism for rotating the piston, including
i. first, second, and third stationary pulleys supporting a first belt in an equilateral triangle configuration, midpoints of first, second, and third segments of the first belt nearly touching first, second, and third points of the cylindrical drive surface,
ii. drive means for rotating the first pulley, thereby rotating the first belt and thereby rotating the second and third pulleys,
iii. first, second, and third moveable idle wheels symmetrically disposed adjacent to the first, second, and third segments of the first belt, and
iv. means for moving the first, second, and third idle wheels against the first, second, and third segments of the first belt, respectively, displacing them inwardly to symmetrically engage three points of the cylindrical drive surface, respectively, causing the dead weight piston assembly to rotate without producing thereon any sustained vertical displacement forces.

5 more elements

A method of operating a dead weight piston pressure measurement device including a cylinder and a piston rotatable in the cylinder and vertically moveable in the cylinder, weight supporting means carried by the piston and supporting a plurality of calibration weights, the method comprising the steps of:

(a) initially supporting weight of the piston by means of an elastic movement limiting device;
(b) rapidly forcing fluid from a fluid source into a volume between the cylinder and the piston until the piston begins to rise;
(c) sensing movement of the piston in an elastic movement zone determined by the elastic movement limiting device to produce a control signal;
(d) substantially reducing the rate of flow of fluid between the cylinder and the fluid source as the piston moves in the elastic movement zone;
and
(e) actuating a drive mechanism in response to the control signal to rotate the piston, the piston rotating in a free-floating equilibrium zone in the cylinder, lubricated by a thin layer of the fluid between the piston and a wall of the cylinder.

3 more elements

A dead weight cylinder pressure measurement device, comprising in combination:

(a) a piston;
(b) a cylinder rotatable about the piston, and vertically moveable about the piston, the cylinder supporting a plurality of calibration weights and a cylindrical drive surface coaxial with the cylinder;
(c) an external fluid source coupled to supply a flow of fluid, the pressure of which is to be measured, into or out of a volume between the cylinder and the piston to vertically move the cylinder about the piston, the combined weight of a dead weight cylinder assembly including the cylinder and the calibration weights accurately indicating the pressure of the gas in the volume when the cylinder is rotating in a free-floating equilibrium condition about the piston;
(d) a drive mechanism for rotating the cylinder, including
i. first, second, and third stationary pulleys supporting a belt in an equilateral triangle configuration, midpoints of first, second, and third segments of the belt nearly touching first, second, and third points of the cylindrical drive surface,
ii. drive means for rotating the first pulley, thereby rotating the belt and thereby rotating the second and third pulleys,
iii. first, second, and third moveable idle wheels symmetrically disposed adjacent to the first, second, and third segments of the belt, and
iv. means for moving the first, second, and third idle wheels against the first, second, and third segments of the belt, respectively, displacing them inwardly to symmetrically engage three points of the cylindrical drive surface, respectively, causing the dead weight cylinder assembly to rotate without producing thereon any sustained vertical or radial displacement forces.

5 more elements

Dependencies are inferred from the claim text.