Z400 quartz spring gravimeter, produced exclusively by Beijing Geological Instrument Factory, is a high-precision instrument for measuring the relative change of ground gravity acceleration. The elastic system of the instrument is made of timely glass, adopts zero reading mode and is equipped with accurate automatic temperature compensation device. It has the characteristics of high sensitivity, wide measuring range, high precision, light weight, small volume, convenient use and simple calculation. It is the instrument with the largest direct reading range of its kind, which not only meets the needs of high-precision gravity measurement, but also is suitable for regional gravity measurement. The main body of the instrument is a white cylinder with an outer diameter of 14cm and a height of 40cm. The net weight of the instrument is 4.5kg, and the appearance is shown in Figure 4-3- 1.
Fig. 4-3- 1 Z400 appearance of quartz spring gravimeter.
The main technical parameters of the instrument are as follows:
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Structure and working principle of Z400 quartz spring gravimeter.
Z400 quartz spring gravimeter is composed of elastic system, optical indicator system, reading system and thermal insulation system. Its main structure is shown in Figure 4-3-2.
Figure 4-3-2 Schematic diagram of internal structure of Z400 quartz spring gravimeter
1. elastic system
The elastic system consists of sensitive device, measurement compensation device and temperature compensation device. Except for the heavy load (white gold ring) and the temperature compensation line of the balancer, the components of the elastic system are all made by melting and welded as a whole, as shown in Figure 4-3-3.
The sensing device consists of main spring 4, torsion wire 3 and load 1. The upper end of the main spring is connected with the connecting rod, and the lower end is connected with the supporting point of the balance body. The front end of the balance body is fixed with a platinum ring. When gravity increases, the balance body deflects downward and the elastic arm decreases; However, when gravity decreases, the balance body deflects upward and the elastic arm increases. The connection mode of the main spring makes the small gravity change cause the balance body to deflect greatly, so it plays a role in assisting the movement itself. The main spring is a zero-length spring made of a time line with a diameter of tens of microns. The front end of the balancer is an indicator line 1 1, which shows its deflection. The range of activities of the balance body is limited. The balancing body has no clamping device.
The measuring compensation device consists of measuring spring 10, measuring spring 6, frame, connecting rod 7 and measuring torsion line 9. Measuring the elastic coefficient of spring is much smaller than measuring the elastic coefficient of spring in range. Their upper ends are respectively connected to the micrometer, and their lower ends are vertically connected to the pillars welded to the frame. When zero reading is used, the measurement compensation device compensates for the change of gravity. When gravity changes, the balance body deviates from zero. At this time, the elongation of the measuring spring can be changed by rotating the micrometer (counter), thus changing the elastic moment acting on the measuring torsion line. The frame and the connecting rod deflect together, so that the balance body returns to zero. The change of micrometer number shows the change of gravity, which makes the balance body return to zero. The change of micrometer number shows the magnitude of gravity change.
Figure 4-3-3 Structure Diagram of Elastic System of Z400 Quartz Spring Gravimeter
The temperature compensation device consists of a temperature compensation line 5, a frame and a connecting rod (the same frame and connecting rod as the measuring compensation device). One end of that temperature compensation wire is connecte with the upper end of the connecting rod,
And the other end is connected with the frame. A pair of temperature compensation twisted wires are welded on both sides of the other end of the connecting rod and connected with the frame. Therefore, when the length of the temperature compensation wire changes due to thermal expansion and contraction, both the connecting rod and the frame will deflect relatively, and the deflection of the connecting rod will lead to the change of the position of the end point on the main spring to compensate the change of the torque on the balancer caused by temperature change. As long as the geometric relationship between devices is accurately adjusted, good temperature compensation effect can be obtained.
The whole elastic system is installed on a cylindrical seat made of hard aluminum and covered with two layers of hard aluminum shielding. To eliminate the influence of air flow and air pressure change. Evacuate the protective cover to a certain degree of vacuum (about 10 ~ 15 mm Hg) and seal it (the base is equipped with an exhaust valve). In order to eliminate the influence of static electricity, a radioactive metal foil is installed next to the limiter. In order to prevent water vapor from condensing, a desiccant is also installed in the inner shield.
2. Optical indication system
The deflection of the balance body in the instrument is observed with the naked eye through the optical system. The optical system consists of eyepiece, ruler, field mirror, objective lens and total reflection prism. The magnification is about 250 times, and the lighting part consists of a bulb and a condenser, as shown in Figure 4-3-4.
The "bright line" seen in the field of vision is the image of the indicator wire at the front end of the balance body. The long line in the middle of the ruler is the "zero line". When the gravity increases, the balance body deflects downward by an angle, and the bright line can be seen to shift to the right from the field of vision; Conversely, when gravity decreases, the bright line will move to the left. When observing, the zero reading method is adopted, that is, the bright line must coincide with the zero line at each reading, and then the value of the counter is read. The lighting power supply is in the shape of a knob on the dashboard, which can be turned on with a light lift. The light pipe has a 45 inclined plane, which can reflect part of the light from the condenser to illuminate the vertical and horizontal planes. In order to adjust the sensitivity by tilting method, there is an eccentricity of 2mm between the objective lens and the center line of the eyepiece. When rotating the seat of the eyepiece, the position of the zero line can be translated left and right.
Figure 4-3-4 Schematic diagram of optical system of Z400 quartz spring gravimeter
3. Measurement and reading system
The system consists of precision micrometer screw, guide device, connecting rod and counter. There are two micrometer screw tables, one for range adjustment, and its upper end is hidden in the range adjustment hole on the instrument panel, as shown in Figure 4-3-2; The upper end of another micrometer screw is matched with the counter on the panel, as shown in Figure 4-3-5, for direct reading. In order to keep the seal inside the instrument, two micrometer screws are connected with the range spring and reading spring through metal bellows. The counter has three numbers. Every time the micrometer screw rotates, the second number changes by one number. The decimals after the unit numbers can be read out according to the110 tick marks on the unit number drum corresponding to the fixed sign line, and the half distance between the110 tick marks can also be estimated. Therefore, the data that can be read from the counter is five significant digits, such as 498.75 grids.
Figure 4-3-5 Schematic diagram of measuring and reading system of Z400 quartz spring gravimeter
Figure 4-3-6 Schematic diagram of thermal insulation system of Z400 quartz spring gravimeter
4. Thermal insulation system and others
The instrument has no electrothermal thermostat. In order to reduce the influence of external temperature change, a thermos bottle is installed inside, and heat insulation material is filled between the thermos bottle and the instrument shell. The container and the upper part of the elastic system are also separated by heat insulation materials to prevent the violent change of external temperature from affecting the interior of the subordinate instrument. The thermal insulation system is shown in Figure 4-3-6.
The side of the instrument shell is equipped with a handle and a battery box, and there are three horizontal adjustment screws at the bottom. Instrument accessories include chassis, internal and external shock absorbers (shock absorbers) and tool box. The surface of the chassis is concave, which can roughly level the instrument. The internal shock absorber is used for manual transportation, and the external shock absorber is used to nest the internal shock absorber when the instrument is transported for a long distance or by car.
(Operation steps of Z400 quartz spring gravimeter
(1) Put the instrument chassis flat and steady.
(2) Carefully take the instrument out of the shock-absorbing box (pay attention to prevent it from colliding with the shock-absorbing box) and gently put it on the chassis, roughly flush with the concave surface of the chassis. Be careful not to let the instrument get too close to the edge of the chassis, so as to avoid the unstable center of gravity and fall on the instrument.
(3) Hold the instrument with the right hand and lift the lighting power switch with the left hand.
(4) Turn the horizontal adjustment screw, first adjust the bubble of the horizontal level to the center, and then adjust the vertical level. After adjusting the level, do not press the instrument panel during the whole operation.
(5) Observe the position of the bright line (indicator line) in the eyepiece barrel. When the bright line is on the left side of the zero line of the scale, turn the counter knob clockwise; On the contrary, when the bright line is on the right, the counter rotates counterclockwise. In order to avoid the influence of gear and pitch clearance on reading, always keep the same rotation direction every time reading, so that the bright line coincides with the zero line. It is customary to turn the reading clockwise a little more, and then move the bright line from left to zero. After the two overlap, write down the reading on the counter at this time (read five significant figures).
(6) Turn the counter counterclockwise for half a turn to make the bright line deviate from the zero line. Repeat step (5).
(7) Repeat step (6) until the maximum difference of three consecutive readings is within the allowable range (generally 0.2 ~ 0.3 grid).
(8) check the vertical and horizontal. If the off-center position of the bubble is within the allowable value (such as 1/2 scale), press the lighting switch and record the time (accurate to "minutes").
(9) Finally, gently lift the instrument and carefully put it back into the impact box, so as to transfer it to the next measuring point for observation.
Inspection and adjustment of Z400 quartz spring gravimeter
In order to ensure the accuracy of instrument measurement, mechanical gravimeters such as Z400 quartz spring gravimeter should be checked for necessary performance before being put into production. Routine inspection includes inspection and adjustment of range, vertical and horizontal level, bubble curve test and sensitivity inspection and adjustment.
(1) Inspection and adjustment of measuring range: Check whether the measuring range of gravimeter is suitable for the observation range of local work area, or make adjustment.
(2) Inspection and adjustment of vertical and horizontal level and bubble curve test: In order to reduce the influence of instrument leveling error on instrument reading, the horizontal position of the instrument should be inspected and tested. Measure the bubble curve and adjust the vertical and horizontal levels. It is required that the measured bubble curve deviates from its correct position by no more than (1/4 ~ 1/2) grids.
(3) Inspection and adjustment of sensitivity: For the light sensitivity of Z400 quartz spring gravimeter, that is, when the bright line deviates from the scale, the reading of the corresponding counter should be adjusted to (16 ~ 20).
(5) Instructions for use of quartz spring gravimeter
(1) Check whether the handles, belts and hooks are in good condition. The firmness of the instrument can eliminate hidden dangers at any time.
(2) When picking and placing instruments, the movements should be gentle, and collision is strictly prohibited.
(3) It is forbidden to tilt, lay flat or invert the instrument at a large angle.
(4) After the instrument is placed on the chassis, the operator shall not walk and leave at will.
(5) When adjusting the level and observing the reading, do not press the instrument panel.
(6) Protect the instrument from direct sunlight and rain.
(7) Turn the counter slowly and evenly.
(8) When the instrument breaks down in the work, it shall not be disassembled at the site without authorization, but shall be brought back to the station for maintenance or sent to the factory for maintenance by personnel with maintenance experience.
(9) After work every day, the instrument should be cleaned once, and the eyepiece or panel should be wiped with a mirror cleaning paper or a soft brush. No other substitutes are allowed. The anchor screws should also be cleaned and lubricated regularly.