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Gas-liquid gravimeter |
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IPC classes for russian patent Gas-liquid gravimeter (RU 2282218):
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FIELD: geophysics. SUBSTANCE: gravimeter comprises mercury column that is balanced by the pressure of gas inside the closed vessel and moves vertically when the gravity changes and capacitive transducer that is used for recording the changes. The inner sides of the bottom parts of the vessels within the range of mercury level displacements is made of concentric spheres whose center is located at the point of the suspension of the plate of the capacitive indicator of the mercury level in the top vessel. The bottom vessel receives the thermal compensator that changes its volume in accordance with the heat expansion of gas so that the pressure of gas remains constant. The actuator of the heat compensator is the thermosensitive member made of a closed vessel filled with the heat compensating liquid. The top base of the vessel is provided with the bellows having movable base secured to the base of the larger bellows that is the top base of the vessel. Two additional spaces filled with the heat compensating liquid are connected with the vessel. The additional spaces are in a heat contact with the mercury column in the connecting pipe and bottom vessel, respectively. EFFECT: expanded functional capabilities. 2 dwg
The invention relates to gravity and can be used for relative measurements of gravity in the surveying and exploration purposes. Most common in practice, static gravimeters, in which the sensor element is a spring loaded probe body. [V.S. Mironov Course gravimetry. Leningrad: Nedra, 1980]. Their main drawback is the instability over time of elastic characteristics of the sensing element (spring), leading to the zero drift of the instrument, the nonlinearity of the dependence of the elastic characteristics of the spring material (metal or quartz) temperature, which complicates temperature compensation in a fairly wide temperature range, and the dependence of the readings from tilting the body of the device, increases the requirements for the alignment and thereby decreasing the performance of film-making works. These shortcomings limit the accuracy of relative measurements of gravity at the level of ±0.01 mGal in the field and ±0.001 mGal in stationary conditions, and the presence of the zero drift of the gravimeter prevents the definition of ¡gravity changes (NIST) rather few tenths of milligals. Closest to the claimed is gas-liquid gravimeter [USSR Author's certificate No. 1241885, CL G 01 V 7/02, 1986], which contains vakuumirovaniya case, which established the topand bottom closed coaxial cylindrical tanks, the lower part of which is made in the form of concentric spheres, partially filled with mercury. They communicate via filled with mercury, a connecting tube. Changes in gravity are determined by the resulting changes in mercury levels in tanks that are registered capacitive transducer. Its stator plates suspended from the casing of flexible traction at a point coincident with the center of the concentric spheres. This configuration ensures the independence of gravimeter readings from the tilt of his body. The upper part of the upper reservoir vacuumed, and in the upper part of the lower tank filled with gas, is rigidly fixed to thermal compensator in the form of a temperature-sensitive element connected to its movable end with a large bellows forming the upper base of the tank. The parameters of thermal compensator is chosen so that the change in the volume of the tank was performed according to the law ΔV=β·V·Δt, where ΔV is the volume increment corresponding to the temperature increment Δt, β - coefficient of volume expansion of the gas, V is the volume of gas in the tank when the temperature of the temperature, i.e. under the law Isobaric expansion of the gas itself. It is obvious that the pressure of gas in the tank 3 will remain constant regardless of its initial value. It is dostatkem this gravimeter are small measuring range, due to use to indicate levels of working fluid (mercury) capacitive transducer with a variable gap between the plates, the impact on measuring thermal expansion of mercury and the temperature gradients in the volume of the device and the complexity of the transport device associated with the absence of locking. In the proposed gravimeter stator plates of capacitive transducer made in the form of electrically interconnected narrow rings of equal width, applied at intervals equal to the width of the rings, on the outer side surface of the wide inner ring of dielectric material. The rotor casing is applied in the form of such rings on the inner side surface of the cylindrical dielectric float larger diameter mounted coaxially with the inner ring with a small radial clearance to him and with the free vertical movement. This configuration of the plates provides a virtually unlimited range of measurements without compromising accuracy. The gravimeter is equipped with a locking made in the form of tightly fitted on the lower part of the float wide rim with sealant around the perimeter and externally managed three mechanical clamps with the possibility of dense sprays rim of the float to the spherical section of the inner surface of the upper reservoir above the level of the I mercury and simultaneous fixing of a rigid metal ring, associated with the inner dielectric ring via elastic elements. To limit the movement of mercury above the surface of the mercury in the lower tank installed semi-permeable wall of the porous glass. The sensing element is made in the form of a closed vessel filled with temperature compensating fluid, the upper base of which is provided with a small bellows with a movable base, rigidly connected with the base of a large bellows. The vessel is connected to two extra volume with temperature compensating fluid being in thermal contact with the amounts of mercury respectively in the connecting tube and into the lower reservoir. These volumes are designed to make full compensation of thermal expansion of the mercury even in the presence of temperature gradients in the volume of the device. In addition, post height, volume, and area of the free surface of the mercury in the upper reservoir, the volume of the submerged portion of the float and the cross-sectional area of the float on the edge of the mercury is chosen so that the current to float the Archimedes force and pressure of mercury at the bottom of the reservoir did not depend on temperature. Conceptual diagram of the proposed gravimeter shown in figure 1. In it the mercury column 1 is the lower part of the upper vacuum vessel 2 and the bottom of the tank with gas 3, as well as the connecting tube 4. Indication of the movements of the upper level of the mercury column due to changes in gravity, is a capacitive transducer with variable area of overlap of the plates, the stator lining which is applied in the form of rings on the outer side surface of non-conductive cylinder 5, is suspended from the casing of flexible traction 6 and is provided with a liquid damper, and rotary plates printed on coax her inner lateral surface of the float 7. The arresting of the gravimeter by means of clamps 8 which presses the float to the walls of the tank 2 and at the same time the locking cylinder 5. A semi-permeable partition 9 in the tank 3 prevents the ingress of mercury in its upper part. System armirovki significantly reduces the requirements for the transportation and storage of the gravimeter. The power of capacitive transducer and the output information via the electrical sensors 10. The temperature compensation in the gravimeter is as follows. When zooming in, for example, the temperature of the liquid in the tank 11 extends and expands the bellows 12 and the associated bellows 13, thereby increasing the volume of the tank 3. With decreasing temperature, on the contrary. The volumes of the tanks 3 and 11, the diameters of the bellows 12 and 13 and the coefficient of volume expansion of the liquid is chosen so that the volume change is of reservoir 3 when the temperature changes occurred according to the law where V is the volume of the reservoir at temperature t, V0- tank at t=0°, β - temperature coefficient of volume expansion of the gas, i.e. the law Isobaric expansion of the gas itself. It is obvious that the pressure of gas in the tank 3 will remain constant regardless of its initial value. The bellows 13 is covered by a protective casing 14. Sealed the gap between the bellows and the casing is filled with the same gas as the reservoir 3, with the same pressure. The space between the casing 14 and the housing 15, as the rest of the volume, vacuumed. Will predifferentiated equation (1) variable t: dV=β·V0·dt. On the other hand, from the requirement of temperature compensation where q is the ratio of the areas of the bases of the bellows 13 and 12, VT- volume of toluene, βTits coefficient of volume expansion, so that the condition of temperature compensation is When q is equal to 5, and thermal expansion coefficients of the liquid and gas, respectively ˜0,001 (toluene) and ˜0,0037 fluid volume is approximately 40% of the volume of the tank. The second largest source of errors is the dependence of the density of mercury ρ temperature t, leading to dependence on the past and the pressure of his mouth the aqueous post R=ρ ·g·N. Here H is the distance between the surfaces of mercury in the upper and lower reservoirs (the height of the column of mercury), g is the acceleration of gravity. In the first approach (without gradients T) the problem of compensation of this dependence is solved simply by an adequate increase in temperature compensating fluid (because of the error introduced by thermal expansion of the gas and mercury, have the same sign). In the presence of temperature gradients, the problem of compensation becomes much more complicated, but in the framework of the following proposed approach has a solution that meets the given us metrological requirements. It is the development of Autonomous systems of temperature compensation for each of the three fragments of mercury, located respectively in the upper tank 1, the connecting tube 2 and the lower tank 3, schematically depicted in figure 2. The introduction of Autonomous systems of temperature compensation, responsive to the integral of the temperature of these fragments, eliminating the necessity of taking into account temperature gradients, greatly simplifies the temperature compensation, reducing her to the approval of thermophysical parameters of the individual elements of a thermodynamic system with their geometrical dimensions. The only constructive innovation - filled with additional amounts of toluene sealed tube 4 mounted coach the constraints of the tube 2 and soamsawali bellows 12 figure 1. To search for correlations between these parameters meet the condition of the temperature stability of the measuring system, we introduce the following notation: H1, The equation of equilibrium of a system of gas - the mercury column is where P is the gas pressure in the lower reservoir. Condition temperature stability of the system in the absence of gradients will be The last summand in the middle part of this equation takes into account the change in gas pressure due to a change in its volume dVt=S·dH2. Taking into account gradients of t, i.e. if t1≠t2≠t3, Both theoretical calculations and practical implementation of temperature compensation in General are greatly simplified with the introduction of Autonomous temperature compensation for Hg H1that boils down to the requirement of the constancy of its contribution to the pressure Hg N, ie, P1=ρ1·g·H1=const where ρ1- the density of mercury at the temperature t1. Then Substituting in this equation the values of and after simple transformations get the value which is easily satisfied by the selection of parameters. When this condition and g=const R1=const. In other words, P1depends only on the acceleration of gravity and changes in t1dynamically not affect the mercury column H2. On the other hand, to ensure the independence of reference for the Converter unit from t1must satisfy the condition of independence from t1also Archimedean force acting on the float. This condition can be expressed as the following obvious relation: FAr=Vfl·ρ1=const (at constant g). Here Vfl- the volume of the submerged portion of the float. Here It is also obvious that where Q is the cross - sectional area of the float on the edge of the mercury. Substituting this expression and the values of the dρ1and dH1from (8) and (9) in (10), we obtain the ratio where the change of Archimedean force by changing the density of mercury is exactly compensated by the change of volume of the submerged portion of the float. As is easily seen, to ensure equality of (13) in the case of cylindrical float to its immersed part should add more volume ΔVfl=Q·h, so that Vfl=Q·(H1-h)+Q·h=Q·H1in accordance with (13). In figure 2 an additional amount shown in the form of a ring 6. Further, from equations (6), (7) to the temperature stability of the equilibrium system gas - mercury column arising from the claim of the absence of dynamic effects of mercury H2on a mercury column H1when changes of temperature t2and t3: In further calculations we will proceed from the obvious fact that even though we compensate the effects of temperature changes, but the very act of compensation - change in the volume of gas in accordance with the changed already the temperature is isothermal process and is described which is the equation d(V·P)=P·dV+V·dP=0, where If instead of dP to put the expression (14), we obtain the change of volume V due to thermal expansion of mercury V2and V3 By analogy with (2) condition of temperature compensation is where in accordance with (14) and (15) Here R is determined by equation (4). The temperature change of the height of the mercury column H2occur due to changes in the level of mercury in the bottom of the tank due to temperature changes in the amounts of mercury V2and V3i.e. Substituting into (17) this expression, as well as dρ2=-ρ2·βHg·dt2R=ρ·g·N, and given that replacement ρ2on ρ not makes a significant contribution to the accuracy of temperature compensation, obtain after simple transformations It is obvious that a stable dynamic equilibrium of the system in the presence of temperature gradients is possible only with independent compensation of the influence of local temperature changes dt2and dt3. This means breaking the equation (19) into two independent equations after the transformations have the final These relations together with (3), (10) and (13) form an independent set easily achievable conditions that are necessary and sufficient to ensure complete temperature stability of the proposed gas-liquid gravimeter. The absence of cross-influence and additivity of these conditions is caused by the fact that in the presence of a temperature level ±0,001°With (which is provided and easy to implement) maximum temperature error, subject to compensation, not to exceed 10-6from the measured values of the acceleration of gravity g. Thus, the proposed gas-liquid gravimeter, in contrast to spring, it is possible precision compensation of the tilt axis of sensitivity of the instrument, as well as temperature and its gradients in the volume of the device. The introduction of Autonomous systems of temperature compensation, responsive to the integral of the temperature of individual nodes, eliminating the necessity of taking into account temperature gradients, greatly simplifies the temperature compensation, reducing her to the approval of thermophysical parameters of the individual elements of a thermodynamic system with their geometrical dimensions. The use of the proposed container of the STN Converter with variable area of overlap of the plates provides a virtually unlimited range of measurements without compromising accuracy. The presence of locking helps to requirements for the transportation and storage of the gravimeter. These advantages, coupled with the absence of zero drift open the possibility of using the proposed gravimeter for registration ¡change gravity in stationary conditions, including due to vertical movements of the earth's crust, and thus to abandon time-consuming and expensive re-geometric nivelirovany. It can be used also in areal gravimetric observations, both on land and at sea. Gas-liquid gravimeter containing vakuumirovaniya case in which there are upper and lower closed coaxial cylindrical tanks, the lower part of which is made in the form of concentric spheres, partially filled with mercury and connected via filled with mercury, a connecting tube, the indicator of the level of mercury in the upper reservoir is in the form of a capacitive transducer, the stator plates which are suspended to the body on the flexible traction at a point coincident with the center of the concentric spheres, with the upper part of the upper reservoir vacuumed, in the top or bottom of the tank filled with gas, is rigidly fixed to thermal compensator in the form of a temperature-sensitive element connected to its movable end with the most the bellows, forming the upper base of the tank, and the parameters of thermal compensator is chosen so that the change in the volume of the tank was performed according to the law ΔV=β·V·Δt, where ΔV is the volume increment corresponding to the temperature increment Δt; β - coefficient of volume expansion of the gas; V - volume of gas in the tank when the temperature of the temperature control, characterized in that the stator plates of the capacitive transducer made in the form of electrically interconnected narrow rings of equal width, applied at intervals equal to the width of the rings, on the outer side surface of the wide inner ring of dielectric material, the rotor casing is applied in the form of such rings on the inner side surface of the cylindrical dielectric float larger diameter mounted coaxially with the inner ring with the free vertical movement with a small radial clearance thereto and provided with a locking made in the form of tightly fitted on the lower part of the float wide rim with sealant around the perimeter and externally managed three mechanical clamps with the possibility of dense sprays the rim of the float to the spherical section of the inner surface of the upper reservoir above the level of mercury while fixate the hard metal rings, associated with the inner dielectric ring via elastic elements, and a semi-permeable walls of the porous glass installed above the surface of the mercury in the lower reservoir, and a temperature sensitive element made in the form of a closed vessel filled with temperature compensating fluid, the upper base of which is provided with a small bellows with a movable base, rigidly connected with the base of a large bellows, while the vessel is connected additional volumes with temperature compensating fluid
where H1,
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