Method of measuring forces in the presence of an external pressure
AssigneeSchlumberger Technology Corporation
InventorsLaurent Demia, Jacques Dugray, Jean-Pierre Trioullier
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Abstract
The invention relates to a method of measuring a force F exerted on a piece in a given direction in the presence of external pressure Pe and temperature T. According to the invention: the response Rcap of a deformation sensor to the total force exerted on the piece is measured; said external pressure Pe and said temperature T are determined; and the force F exerted on the piece in said given direction is determined by a relationship between the response of said deformation sensor (Rcap) and a polynomial function of degree n of the pressure Pe [fn(Pe)], said relationship being such that: F=K.Rcap−fn(Pe) where K is a constant determined by calibration of the sensor.
Claims13
1/ a method of measuring a force f exerted on a piece in a given direction, in the presence of an external pressure Pe and a temperature T, the method being characterized in that:
- the response Rcap of a deformation sensor to the total force exerted on the piece is measured;
- said external pressure Pe and said temperature T are determined;
- and
- the force F exerted on the piece in said given direction is determined by a relationship between the response of said deformation sensor (Rcap) and a polynomial function of degree n of the pressure Pe [fn(Pe)], said relationship being such that:
- F=K.Rcap−fn(Pe)
- where K is a constant determined by calibration of the sensor.
2/ A method according to claim 1, characterized in that the force F exerted on the piece is determined by the relationship:
- 9 F = K · R cap - ∑ i = 0 n A i ( T ) · Pe i
- the coefficients Ai(T) being a function of temperature T and being determined experimentally.
3/ A method according to claim 2, characterized in that the coefficients Ai(T) are polynomial functions of temperature and of order m such that:
- 10 A i ( T ) = ∑ j = 0 m B ij · T j
- where the coefficients Bij are determined experimentally.
4/ A method according to claim 2 or 3, characterized in that the function fn(Pe) is a second-order polynomial function of pressure Pe (n=2).
5/ A method according to any one of claims 2 to 4, characterized in that the coefficients Ai(T) are second-order polynomial functions of temperature (m=2).
6/ A method according to any one of claims 2 to 5, characterized in that the coefficient K is determined by a mechanical traction/compression test at constant temperature, the pressure Pe acting on the deformation sensor being assumed to be zero.
7/ A method according to claim 6, characterized in that the coefficient K is given by the slope of the straight line whose equation is as follows:
- F=K.Rcap−A0(T)
8/ A method according to any one of claims 2 to 7, characterized in that the coefficients Ai(T) are determined by a test under pressure and temperature, the force F exerted on the pressure measurement means being assumed to be zero.
9/ A method according to claim 8, characterized in that the coefficients A0(T), A1(T), and A2(T) are determined by second-order polynomial interpolation of the following curve:
- K.Rcap=A2(T).Pe2+A1(T).Pe+A0
10/ A method according to claim 9, characterized in that the coefficients A0(T) and A1(T) are assumed to be constant with temperature and the coefficient A2(T) is assumed to be zero.
11/ A method according to claims 5 and 10, characterized in that the force F exerted on the piece is given by the following matrix relationship:
- 11 F = K · R cap - ( 1 Pe Pe 2 ) · ( B 00 0 0 B 10 0 0 0 0 0 ) · ( 1 T T 2 )
12/ A method according to any preceding claim, in which the force exerted on a cylindrical test piece (1) is measured, the method being characterized in that the measurement means (4) is situated on a portion (2) of the test piece that is of reduced diameter (D2).
13/ A method according to any one of claims 1 to 11, in which the force exerted on a tubular test piece (10) is measured, the method being characterized in that the measurement means (40) is situated on an insert (20) connected via studs (30) to the inside walls of said test piece (10).