JP2006084311A - Magnetic levitation density meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable precise density measurement with a magnetic levitation density meter. <P>SOLUTION: Supporting member locking stage sections 44 are projected on the bottoms of a first weight 21 and second weight 23 having different density and known volume, only one of the weights is supported and only tares of a load change member 33 and a permanent magnet 36 are also supported by a first weight supporting member 37 and a second weight supporting member 34 of a load change member 33 of which upper end is fixed to the permanent magnet 36 sucked by an electromagnet 18. The position of the load change member 33 is detected by a position sensor 28, and it is vertically moved by an actuator 17 and held at a stable position with zero power control. The load change member 33 changes the support state of the weight or the like with rotation of the actuator 17, weighing is made by an electronic balance at a tare weighing position, a first weight weighing position, and a second weight weighing position so that the levitated position of the permanent magnet 36 does not vary, and a magnetic force acting on fluid is corrected, and precise density measurement is made. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic levitation density meter that measures the density of a fluid by levitation of a weight in a fluid using magnetic levitation and measuring the mass of the weight at the time of receiving buoyancy by the fluid.

  Conventionally, there are various types of submerged weighing devices that use magnetic levitation. FIG. 4 schematically shows a known magnetic levitation density meter shown in Non-Patent Document 1 below. A container 51 made of a high-pressure-resistant cell has a partition wall 52 formed in the middle, and is divided into an upper space 53 and a lower space 54, and both spaces are isolated by the partition wall 52 so that fluid cannot flow. In the upper space 53, an electromagnet 55 is suspended from an electronic balance 68 disposed above in the vicinity of the upper surface of the partition wall 52, and an arbitrary electromagnetic force can be generated by controlling the voltage from the control device.

  A weight placing step portion 56 is formed below the lower space 54 so that the weight 57 can be placed under its own weight. The mounting step portion 56 is provided with a central hole 58 so that an external fluid can be introduced, whereby the lower space 54 is filled with the fluid 59. A position sensor 61 is disposed around the center hole 58, and the position of the lower end portion 65 formed in the lower portion of the weight support portion 64 is determined in the load exchange member 63 extending through the center through hole 62 of the weight 57. In the center hole 58, detection is made without contact.

  A permanent magnet 66 disposed in the vicinity of the lower surface of the partition wall 52 is fixed to the upper end portion of the load exchange member 63, and the load exchange member 63 integrated with the permanent magnet 66 moves up and down. Is detected by the position sensor 61. The weight support portion 64 is located below the bottom surface 67 of the weight 57 placed on the weight placement step portion 56 in FIG. 4A, and the weight support portion 64 is weighted in FIG. 57 is supported and lifted upward.

  In the magnetic levitation density meter having the above-described configuration, the position sensor 61 detects the position of the lower end portion 65 of the load exchange member 63 to which the permanent magnet 66 is fixed, and controls the conduction voltage of the electromagnet 55 to control the magnetic force. By adjusting, the load exchange member 63 can be stably levitated.

  By adjusting the floating position at this time, the voltage applied to the electromagnet 55 can be made zero, and the heat generation of the electromagnet 55 can be suppressed. This is called zero power control.

  The sum of gravity and buoyancy acting on the load exchange member 63 at this time is weighed by an electronic balance 68 positioned above. FIG. 4A shows a tare weighing position. As described above, the weight support portion 64 provided on the load exchange member 63 is separated from the bottom portion 67 of the weight, and the load exchange member 63 and the permanent magnet 66 are in the fluid 59. As a result, the apparent mass of only the load exchange member 63 is measured by the electronic balance 68, and a tare weighing position for measuring the tare as a measuring mechanism is obtained.

  On the other hand, FIG. 4B shows a state in which the permanent magnet 66 is lifted and all the objects including the weight 57 are lifted after the weight support part 64 comes into contact with the bottom part 67 of the weight 57. The whole is supported in a state where it is stopped at a predetermined position by energization control of the electromagnet 55 by the signal of the position sensor 61, and the total load is measured by the electronic balance 68 here. The position of the permanent magnet 66 at this time is positioned above the position shown in FIG. This state is a weight weighing position for weighing the weight including the tare.

When the load exchange member 63 is in the tare weighing position and the weight weighed position as described above, the mass M _A and M _B the apparent be weighed by the electronic balance 68, when excluding the mass of the electromagnet or the like,
A: M _A = (ρ ₃ −ρ ₁ ) V ₃ (1)
B: M _B = (ρ ₃ −ρ ₁ ) V ₃ + (ρ ₂ −ρ ₁ ) V ₂ (2)
It becomes. ρ is density, V is volume, subscripts 1, 2, and 3 are fluid, weight, and load exchange member, respectively.
By subtracting Equations (1) and (2) side by side,
B−A: M _B −M _A = (ρ ₂ −ρ ₁ ) V ₂ (3)
Therefore,
_{ρ 1 = ρ 2 - (M} B -M A) / V 2 (4)
As a result, the density of the fluid 59 is obtained.

In this method, the magnetic levitation by the electromagnet 55 and the permanent magnet 66 can be used to measure the density of the fluid 59 in a non-contact manner, so that the fluid is sealed in a container 51 such as a high-pressure cell and the balance cannot be used. Density measurement is possible even under high temperature and high pressure conditions.
Wagner, R and Kleinrahm, R. Densimeters for very accurate density measurements of fluids over large ranges of temperature, pressure, and density, Metrologia41 (2004), S24-S39. Kuramoto, N., Fujii, K. and Waseda, A. Accurate density measurements of reference liquids bya magnetic suspension balance, Metrologia 41 (2004), S84-S94.

  The conventional measurement method is based on the premise that force is completely transmitted between the electromagnet 55 and the permanent magnet 66, but actually, the container 51 and the measurement fluid as a high-pressure cell other than these are used. Although 59 is weak, it attracts or repels the magnet, resulting in a force transmission error. Among these, the force transmission error due to the container 51 can be corrected by measuring in a state where the lower space 54 is evacuated. However, the transmission error due to the fluid 59 cannot be corrected by the same method, and calibration must be performed using two types of fluids whose susceptibility and density are known. However, in general, the magnetic susceptibility of the fluid is very small, and the model used for the calculation is incomplete, so the relative uncertainty of the correction amount is large. In the fluid density measuring apparatus using the most accurate magnetic levitation at present, this point is the biggest cause of uncertainty, which is described in Non-Patent Document 2 above.

  As described above, the main factor of density measurement uncertainty due to fluid magnetism in the above-described conventional method is that the floating position changes between the tare weighing position and the weight weighing position, so that the magnetic field is strong between the electromagnet 55 and the permanent magnet 66. This is because if the amount of fluid existing in this region is different, the difference in magnetic force received by the fluid is not canceled out. Furthermore, even if the floating position is the same, if the attractive force acting between the magnets is different, the distribution of the magnetic field lines changes, so the magnetic force acting on the fluid is not constant.

  Therefore, the present invention prevents the position of the permanent magnet in the fluid from differing between the tare weighing position and the weight weighing position, and further corrects the influence of the magnetic properties of the fluid caused by the difference in magnetic force between the two positions, thereby providing a precise density. The main purpose is to provide a magnetic levitation density meter capable of measurement.

  In order to solve the above-mentioned problem, the present invention has, as its basic technical idea, a load exchanging member that has a degree of freedom to rotate in addition to vertical movement, and further, an electromagnet suspended from a balance is moved up and down. It is possible to take the tare position or the measurement position, whereby the tare and the measurement can be performed at the same position, and most of force transmission errors due to the magnetic force of the fluid can be offset.

  In addition, two weights with known density and volume are prepared, and the rate of change in magnetic force acting on the fluid at the same measurement position is obtained from these weighed values, and the force transmission error due to the change in magnetic field distribution can be corrected. I was able to do it.

  More specifically, the above problem is solved by the following means. That is, the magnetic levitation densitometer according to the present invention includes two weights having different densities and known volumes, and a load exchange member that replaces the two weights in a measurement fluid or does not place a weight. An electronic balance for measuring the load, a magnetic levitation mechanism for propagating the load including only the weight exchange member or any weight to the electronic balance in a non-contact manner, and levitation of the load exchange member An actuator for controlling position and load exchange, and a tare measurement position where no weight is placed by the electronic balance, a first density measurement position where only one weight is placed, and a second density measurement where only another weight is placed The weighing is performed by arbitrarily setting the position.

  Another magnetic levitation densitometer according to the present invention is the magnetic levitation densitometer, wherein the load exchange member includes a rod penetrating the center hole of two weights, a first weight support member fixed to the rod, and a second weight support member. A weight support member and a permanent magnet provided at the upper end portion are provided, and a magnetic levitation mechanism for lifting the permanent magnet with an electromagnet is provided.

  Another magnetic levitation densitometer according to the present invention is the magnetic levitation densitometer, wherein the load exchange member is selectively provided on a weight support step protruding from a bottom surface of each weight and a bottom surface not provided with the support step. A weight support member that abuts is provided, the load exchange member is rotated by the rotation of the actuator, and the weight is replaced by the rotation of the weight support member.

  Another magnetic levitation density meter according to the present invention is characterized in that, in the magnetic levitation density meter, each of the two weights is composed of one Si single crystal and one Ge single crystal.

  Since the present invention is configured as described above, the influence of the position of the permanent magnet in the fluid at the tare weighing position and the weight weighing position is prevented, and further, the influence of the fluid magnetism caused by the difference in magnetic force at both positions. Can be corrected to a magnetic levitation densitometer capable of precise density measurement.

  In the magnetic levitation density meter, the present invention prevents the influence of the position of the permanent magnet in the fluid at the tare weighing position and the weight weighing position, and further corrects the influence of the fluid magnetism caused by the magnetic force difference at both positions. To measure the load, two weights with different densities and known volumes, a load exchange member that replaces the two weights in the measurement fluid, or a state in which no weight is placed, and the load An electronic balance, a magnetic levitation mechanism for propagating a load including only the weight exchange member or any weight to the electronic balance in a non-contact manner, and controlling a floating position and load exchange of the load exchange member A tare measurement position where no weight is placed by the electronic balance, a first density measurement position where only one weight is placed, and only another weight. It was resolved by performing a second density measurement position and the arbitrarily set to weighing.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 schematically shows a magnetic levitation density meter 11 according to the present invention. A container 12 made of a high pressure resistant cell is formed with a partition wall 13 in the middle as in the conventional case, and is divided into an upper space 14 and a lower space 15. An electromagnet 18 is suspended in close proximity to the upper surface of the partition wall 13 from an electronic balance 16 disposed above in the upper space 14 via an actuator 17, and generates an arbitrary electromagnetic force through voltage control from a control device. It is possible.

  A first weight placing step portion 20 is formed at a substantially middle portion of the lower space 15 so that the first weight 21 can be placed by its own weight on the first weight placing step portion 20. Further, a second weight placing step 22 is formed below the second weight 23 so that the second weight 23 can be placed under its own weight. The second weight mounting step 22 is provided with a central hole 24 so that an external fluid can be introduced. Similarly, the first weight mounting step 20 is also provided with a through hole 25 so that the fluid to be measured can flow. Thereby, the fluid to be measured 26 is filled in the entire lower space 15.

  A position sensor 28 is arranged around the center hole 24, and in the load exchange member 33 extending through the center through hole 30 of the first weight 21 and the center through hole 31 of the second weight 23, in the vicinity of the lower end. The position of the lower end portion 35 formed at the lower portion of the second weight support member 34 is detected in the center hole 24 without contact.

  A permanent magnet 36 disposed in proximity to the lower surface of the partition wall 13 is fixed to the upper end portion of the load exchange member 33, and a first weight support member 37 is provided below the first weight 21, The position sensor 28 detects the position where the load exchange member 33 integrated with the permanent magnet 36 including the second weight support member 34 moves up and down. Further, by bringing the electromagnet 18 and the permanent magnet 36 close to each other, a load acting on the permanent magnet 36 side can be transmitted to the electromagnet 18 side in a non-contact manner, thereby forming a magnetic levitation mechanism.

  The first weight 21 and the second weight 23 have the same configuration. If the second weight 23 is described as an example, the first weight 21 and the second weight 23 are configured as shown in the perspective view of FIG. A relative rotational movement as shown in 1 (c) to (e) is performed. That is, in the second weight 23, the lower end surface 43 of the weight main body portion 40 is provided with three support member locking step portions 44 in the illustrated embodiment.

  A variety of weights can be used, but considering the thermal expansion property, compressibility, reproducibility of measurement, complete isotropic orientation, further low density, and chemical stability, It is preferable to use a single crystal Si material. In addition to those having the above-mentioned performance, it has been clarified by research by the present inventors that Ge is also suitable as a material for a single element single crystal.

  As shown in FIG. 1 (b), three weight support portions 47 are fixed to the rod 45 of the load exchange member 33 at positions corresponding to the engagement grooves 46 in the three support member locking step portions 44. Thus, in the state of the support member position [A] shown in FIG. 1C, the weight support portion 47 engages with the engagement groove 46. Further, as will be described later, when the actuator 17 rotates the permanent magnet 18 by 40 degrees in the illustrated embodiment, only the load exchange member 33 is similarly rotated by 40 degrees, and the support member position [ B] and the support member position [C] in FIG. 1 (e), the two weight support portions 47 are not engaged with the support member locking step portion 44 and are not in contact with the lower end surface 43, but are close to each other. To take.

  Note that the rotation of the weight support portion 47 is performed at a position where the support member locking step portions 44 of both weights and all the weight support portions 47 do not interfere with each other as shown in FIG. A rotation operation is performed.

  In addition, such rotation of the weight support portion 47 is caused by making the first weight support member 37 and the second weight support member 34 have different phases by 40 degrees as shown in FIG. 2A, for example. The support member 37 is arranged to be at the support member position [C], and the second weight support member 34 is arranged to be at the support member position [B]. Thereafter, the load exchanging member 33 is rotated by 40 degrees by the actuator 17 so that the first weight support member 37 in FIG. 2B becomes the support member position [A], and the second weight support member 34 supports it. 2C, the first weight support member 37 in FIG. 2C is the support member position [B], and the second weight support member 34 is the support member position [A]. Thereafter, it is possible to return to the position of FIG. 2A again.

  In the above embodiment, an example is shown in which the present invention can be implemented even if the load exchanging member 33 always rotates in one direction. By doing so, each state of FIG. 2A, FIG. 2B, and FIG. 2C may be obtained.

The actuator 17 is fixed to the upper rod 48 suspended from the electronic balance 16, and the actuator 17 rotates the weight support portion 47 by 40 degrees as described above, and can also be controlled in the vertical direction.
The electromagnet 18 is fixed to the lower end of the lower rod 49 extending downward from the actuator 17. The electromagnet 18 is suspended close to the upper surface of the partition wall 13, and the permanent magnet 36 disposed close to the lower surface of the partition wall 13 via the partition wall 13 is controlled at a voltage of zero by energization control from the control device. It can be stably stopped at the position where it rises.

  The electromagnet 18 and the permanent magnet 36 are non-axially structured, so that the permanent magnet 36 can be rotated following the rotation of the electromagnet 18 and the vertical movement can also be tracked. The load exchange member 33 can be arbitrarily moved up and down and rotated while maintaining zero power control. Both the first weight 21 and the second weight 23 arranged in the container 12 composed of the high-pressure cell have known density and volume, and only the load exchange member 33 or the load exchange is performed by the rotation of the load exchange member 33. Either the member 33 and the first weight 21 or the second weight 33 can be levitated.

  When the first weight support member 37 is at the support member position [C] and the second weight support member 34 is at the support member position [B], for example, as shown in FIG. All of the weight support portions 47 of the first weight support member 37 and the second weight support member 34 do not engage with the weight support step portion 44 and are in a free state. By measuring the sum of gravity and buoyancy acting on the load exchange member 33 and the permanent magnet 36 at this time with the electronic balance 16, the tare supporting the weight can be weighed.

From this state, the load exchanging member 33 is lowered to the state shown in FIG. 1A, the electromagnet 18 is rotated 40 degrees by the actuator 17, and the permanent magnet 36 is rotated in the same manner, thereby supporting the first weight. The member 37 is the support member position [A], and the second weight support member 34 is the support member position [C]. As a result, the three weight support portions 47 of the first weight support member 37 are engaged with the engagement grooves 46 of the weight support step portion 44, and the second weight support member 34 is in a free state position. The load exchange member 33 is raised while supporting only the first weight 21 by the actuator 17 while maintaining zero power control from the state.
Thereby, the stable state shown in FIG. 2B is obtained, and the electronic balance 16 is measured in the same manner as described above, and the total weight of the first weight and the tare is measured.

Thereafter, the load exchange member 33 is lowered again to the position shown in FIG. 1A, and the load exchange member is brought into a free state and rotated by 40 degrees in the same direction. As a result, as shown in FIG. 2C, the first weight support member 37 is in the support member position [B], the second weight support member 34 is in the support member position [A], and the second weight support member 34 is in the second weight. It becomes possible to engage with the 23 weight support steps. As a result, the three weight support portions 47 of the second weight support member 34 are engaged with the engagement grooves 46 of the weight support step portion 44, and the first weight support member 37 is in a free position where it is not engaged. From this state, the load exchange member 33 is raised while supporting only the second weight 23 by the actuator 17 while maintaining zero power control.
As a result, the stable state shown in FIG. 2C is obtained, where the electronic balance 16 is measured in the same manner as described above, and the total weight of the second weight and the tare is measured.

  Using the mechanism as described above, the tare weighing position in FIG. 2 (a), the first weight weighing position in FIG. 2 (b), and the second weight weighing position in FIG. 2 (c) can be obtained. The position of the permanent magnet 36 at each weighing position is constant, and the distance L between the bottom surface of the partition wall 13 and the permanent magnet 36 can be constant. Accordingly, the position of the permanent magnet in the fluid differs between the tare weighing position and the weight weighing position as in the conventional one, thereby preventing the influence of the magnetic properties of the fluid.

  Further, as described above, in the present invention, by performing weighing as described above using two weights whose density and volume are known, the rate of change in magnetic force acting on the fluid at the same measurement position can be determined from these measured values. Thus, it is possible to correct a change in force transmission error caused by the strength of the magnetic field lines. That is, FIG. 3 shows the magnitude of the magnetic force acting on the fluid using the finite element method when the position of the electromagnet 18 is changed while the permanent magnet 36 is levitated at the same position and the attractive force acting on both is changed. This is a calculated example. When the apparent mass applied to the load exchange member 33 changes from 50 to 200 gf, the magnetic force acting on the fluid changes linearly from 2.3 to 2.6 mg. Therefore, the error due to the magnetic force of the fluid at the tare weighing position and the weight weighing position can be suppressed to 0.2 mgf with respect to the change in suction force of 100 gf.

Size F _L of the magnetic force of the fluid from Figure 3
F _L = α F + β (5)
It becomes. Here, F represents a suction force, and α and β represent constants, respectively. Assuming that the apparent masses weighed by the electronic balance 16 at the tare weighing position, the first weight weighing position, and the second weight weighing position are M _A , M _B , and M _C , respectively,
M _A = (α + 1) (ρ ₃ −ρ ₁ ) V ₃ + β (6)
M _B = (α + 1) {(ρ ₃ −ρ ₁ ) V ₃ + (ρ _2a −ρ ₁ ) V _2a } + β (7)
M _C = (α + 1) {(ρ ₃ −ρ ₁ ) V ₃ + (ρ _2b −ρ ₁ ) V _2b } + β (8)
ρ is density, V is volume, subscripts 1, 2a, 2b, and 3 are fluid, first weight, second weight, and load exchange member, respectively. If you subtract (6) from (7) and (8),
M _B −M _A = (α + 1) (ρ _2a −ρ ₁ ) V _2a (9)
M _C −M _A = (α + 1) (ρ _2b −ρ ₁ ) V _2b (10)
Further, when dividing equation (9) and equation (10) side by side, ρ ₁ = {(M _C −M _A ) V _2a ρ _2a − (M _B −M _A ) V _2b ρ _2b } / {(M _C −M _{A) V 2a - (M B} -M A) V 2b} (11)
Thus, the fluid density ρ ₁ can be obtained. Accordingly, it is possible to perform density calculation in which even a minute magnetic force change acting on the fluid when the attractive force changes is corrected while the floating position is constant.
Since weighing is performed using two weights whose density and volume are known as described above, it is necessary to make the densities of the two weights different from each other. A weight made of such a Ge single crystal is used.

It is explanatory drawing of the Example of this invention, (a) is sectional drawing which shows the positional relationship of each member in a weight support member rotation movement position, (b) is a perspective view of a weight and a weight support member, (c) is a support member position [A], (d) is a support member position [B], and (e) is a perspective view and a bottom view showing the support member position [C]. It is sectional drawing which shows the various states of the Example of this invention, (a) shows the tare weighing position, (b) shows the 1st weight weighing position, (c) shows the 2nd weight weighing position. It is a graph which shows the example which analyzed using the finite element method the relationship between the attractive force when making a floating position constant, and the magnetic force which acts on a fluid. It is sectional drawing which shows a prior art example, (a) shows a tare weighing position, (b) shows a weight weighing position.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Magnetic levitation density meter 12 Container 13 Bulkhead 14 Upper space 15 Lower space 16 Electronic balance 17 Actuator 18 Electromagnet 20 1st weight mounting step part 21 1st weight 22 2nd weight mounting step part 23 2nd weight 24 Central hole 25 Through hole 26 Fluid to be measured 28 Position sensor 30 Center through hole 31 Center through hole 33 Load exchange member 34 Second weight support member 35 Lower end portion 36 Permanent magnet 37 First weight support member 40 Weight main body portion 43 Lower end surface 44 Support member engagement Stop part 45 Rod 46 Engaging groove 47 Weight support part 48 Upper rod

Claims (4)

Two weights of different density and known volume,
A load exchanging member that replaces the two weights in the measurement fluid or puts no weight on the fluid;
An electronic balance for measuring the load;
A magnetic levitation mechanism for propagating a load including only the load exchange member or any weight to the electronic balance in a non-contact manner;
An actuator for controlling the floating position of the load exchange member and load exchange;
A tare measurement position where no weight is placed, a first density measurement position where only one weight is placed, and a second density measurement position where only another weight is placed are arbitrarily set and weighing is performed using the electronic balance. Magnetic levitation density meter. The load exchange member includes a rod penetrating the center hole of two weights, a first weight support member and a second weight support member fixed to the rods, and a permanent magnet provided at an upper end portion,
The magnetic density meter according to claim 1, further comprising a magnetic levitation mechanism that lifts the permanent magnet with an electromagnet. The load exchange member includes a weight support step that protrudes from the bottom surface of each weight, and a weight support member that selectively contacts a bottom surface that does not include the support step portion.
The magnetic density meter according to claim 1, wherein the load exchange member is rotated by the rotation of the actuator, and the weight is replaced by the rotation of the weight support member. 2. The magnetic density meter according to claim 1, wherein the two weights are each composed of one Si crystal and one Ge crystal.