DE2618759A1 - Acceleration meter using oscillating quartz system - arranged so that inertial acceleration force acts on weight at moving end of quartzes - Google Patents

Abstract

Acceleration meter has oscillating quartz arrangement for moving objects determining oscillation frequency for detection of acceleration based on a change of the output oscillation frequency. The ends of two or more oscillating quartzes (1, 2) are fixed one another, so that their main faces are opposite. A gap or space is formed between the oscillating quartzes (1, 2). A weight is provided at the moving end of the oscillating quartzes (1, 2). Inertial force is produced during the acceleration of the moving object. It acts on the weight in the direction opposite to the direction of acceleration in order to maintain the original state.

Description

Accelerometer

The invention relates to an accelerometer with a quartz oscillator arrangement for a moving object that is part of an electrical oscillating circuit, in such a way that the crystal or quartz oscillators are used as parts of an element for determination the frequency of the electrical oscillation to detect the acceleration on the The basis of a change in the output oscillation frequency of the circuit arrangement is used or serve.

Due to the advancing miniaturization of electronic circuit arrangements For example, it is possible to use an integrated transmitter or transducer to be placed within a cavity of the accelerometer, so that a quartz crystal accelerometer is obtained, which is very handy due to its small dimensions and the Can dynamically detect movement of an object at a fixed point.

If an external force acts on oscillating quartz crystals, it changes the resonance frequency of the crystal. This phenomenon becomes according to the invention exploited for the production of a Schwingqunarz accelerometer.

An embodiment of the invention is shown in the drawing and is described in more detail below. They show: FIG. 1 a schematic representation, which exemplifies the measuring principle on which the invention is based, 2 shows a longitudinal section through an embodiment of the invention; Fig. 3 a Schematic representation, which in the arrangement according to FIG. 2 according to the invention illustrates temperature compensation made; Fig. 4 is a diagram to which the Characteristic curves of the two quartz crystals used according to the invention with regard to the Frequency change in the resonance frequency depending on the load are; 5 is a graph showing the frequency change as a function of the temperature illustrates; and FIG. 6 is a graph showing the mechanical vibration characteristics of a moving system.

1 illustrates the measuring principle on which the invention is based and shows schematically the arrangement of two quartz oscillators, the reference number 1 the first plate-shaped quartz crystal and the reference number 2 the second plate-shaped Quartz crystal, reference number 3 an electrode that connects to an electrical Circuit arrangement produces, the reference number 4 a spacer, the reference number 5 denotes a mounting plate and the letter W denotes a weight.

The first quartz crystal 1 and the second quartz crystal 2 are mutually exclusive arranged opposite and fixed with one End on the mounting plate 5 and attached at the other end to the spacer 4 and thus to one another connected, whereby relative to the weight W on the side of the mounting plate 5 a fixed, immobile end and relative to the weight W on the side of the spacer 4 a movable, free end of the arrangement is formed.

In general, the electrical resonance frequency (frequency of the electrical natural oscillation, which is to be referred to as the electrical resonance frequency in the following) of a quartz oscillator, which carries out so-called thickness oscillations, i.e. oscillations in the direction of its thickness, changes proportionally to the stresses caused by a weight (or the Amount of deformation due to the stresses of the quartz crystal), regardless of the type of stress generated by a load, which can be expressed by the following equations: In equations (1) and (2), f denotes the resonance frequency, af the amount of change in the resonance frequency, F the tensile or compressive stress resulting from the force exerted on the quartz crystal, Cij the elastic constant of the quartz crystal, t the thickness of the quartz crystal and p is the density of the quartz crystal.

The deflection of the free end of two oppositely arranged plates due to a load or load W can be determined with the help of the equation for the curve of a cantilever beam: In equation (3), v denotes the deflection of the tip of the cantilever, W the load, t the length of the long side (horizontal direction) of the quartz crystal, 'b the length of the short side (non-horizontal direction) of the quartz crystal, Ah the distance between two quartz crystals, t is the thickness of the quartz and E is the modulus of elasticity.

It is now known that the voltage F is proportional to the amount of deflection so that, using equations (1) and (3), it follows that the deflection of the tip of a quartz crystal is proportional to changes is the load W as well as the resonance frequency of the quartz crystal.

Fig. 4 is a graph showing the measurement results for the two quartz crystals shown in FIG. 1 are applied. In the diagram is with (a) the characteristic of the first quartz crystal and with (b) the characteristic of the second Called quartz crystal. Each of the two plate-shaped quartz crystals is made from an element that has the same characteristic curve of the normalized frequency change Af / f as a function of the voltage (load W).

The characteristics (a) and (b) run in the opposite direction, however, it can be seen that the absolute values of the frequency change ratio 8 f / f are the same. This is due to the fact that there is a tensile force at first Quartz oscillators and a compressive force act on the second quartz oscillator and the absolute ones Amounts of the tensile force and the compressive force are equal in a range in which the The tip deflection of the quartz crystal is not that great.

In the following, with reference to FIGS. 2, 3, 5 and 6 shows an embodiment of the quartz oscillator accelerometer according to the invention using the principles described above.

In the present embodiment of the invention, a plate-shaped Quartz oscillator (hereinafter also referred to as a quartz oscillator plate designated) used as a quartz resonator or quartz oscillator.

In Fig. 2 is in the form of a central longitudinal section of the invention Quartz crystal accelerometer illustrated, with reference number 1 being the first Quartz oscillator plate, the reference number 2 the second quartz oscillator plate, the reference number 3 an electrode for connecting an electrical circuit arrangement, the reference number 4 a connecting part, the reference number 5 a base block, the reference number 6 a pin-like block Element, reference number 7 two bearing journals, reference number 8 a bellows, the Reference number 9 a weight, reference number 10 a displaceable component, the reference number 11 a housing, reference numeral 12 an adjusting hole, reference numeral 13 a locking screw for the adjustment hole, the reference numeral 14 is a filling hole for a damping medium, the Reference number 15 a screw plug for the filling hole, reference number 16 a filling hole for inert gas, the reference number 17 holes for mounting screws, the reference number 18 a first cavity formed by the housing 11, the bellows 8, the weight 9, etc., and the reference numeral 19 denotes a second cavity within the bellows 8.

The fixed ends of the first quartz crystal plate 1 and the second Quartz crystal plate 2, the largest areas of which are opposite one another, are inserted or inserted into the base block 5, while the free ends of the Quartz crystal plates are firmly held together by the connecting part 4.

The weight 9 has a screw device and is displaceable with the Element 10 connected by means of a screw connection, the weight 9 such is designed that when turned by means of a screwdriver in the direction the horizontal of the two quartz crystal plates 1 and 2 by means of the movable Element 10 is moved, with the weight 9 and the two quartz oscillating plates 1 and 2 existing Arrangement sliding between the on the weight 9 provided support pin 7 and the cylindrical pin 6, which is fixed to the connecting part 4 is attached, is held.

The bellows 8 is fixed to the base block 5 and the sliding one Element 10 connected, and the second cavity 19 is vcn the base block 5, the Bellows 8, the displaceable element 10 and the weight 9 are formed.

The housing 11 is provided with an adjustment hole 12 through which the Weight 9 slid in the direction of the two quartz crystal plates 1 and 2 is used to set the 3 position of the weight 9, and also screws are öc: her 17 provided in the housing 11 to the accelerometer according to the invention to be attached to an object to be measured, while in the base block 5 also a Filling opening 16 for filling inert gas, such as dry nitrogen, is provided in the second cavity within the bellows 8 so that the housing 11 and the base block 5 surround two oscillating quartz plates 1 and 2, which are held by the bellows 8 are enclosed and thus the interior of the arrangement is airtight is.

After the position of the weight 9 has been set via the adjustment hole 12 is, this hole is closed by means of a locking screw 13. At this VersEhlußschradbe 13, a filling hole 14 is provided through which a damping medium in the form of a viscous substance, such as silicone oil, into the first space 18 can be filled, whereupon the filling hole 14 through the screw plug 15 is closed.

The filling hole 16 provided in the base block 5 is e.g.

sealed by synthetic resin after inert gas into the second cavity 19 has been filled within the bellows 8.

The reason why the weight 9 is in the horizontal direction of the quartz crystal plates is movably or displaceably arranged, is that as a result, deviations in terms of the force-frequency dependency and mechanical Resonance frequency by changing the position of the bearing journals when Forces can be balanced or corrected, with these deviations or Error due to a certain spread or division of the at the same acceleration forces acting on the two quartz crystal plates 1 and 2 can arise and then lead to differences in the resonance frequency.

In particular, the displacement of the weight 9 is due to a a certain force is converted into a bend of the two quartz crystal plates 1 and 2, where the extent or amount of deflection by moving the positions of the Support pin 7 can be changed and thus the tensile force and the compressive force, which act on the first quartz oscillating plate 1 and the second quartz oscillating plate 2, can be set or regulated.

The damping medium filled into the first cavity 18 restricts the mechanical vibration of the weight 9, thereby damaging the oscillating quartz plates due to mechanical resonance as well as the usual display of a measured Value is prevented.

If the mass corresponding to the weight is denoted by m, the spring constant or elastic constant of the quartz plate is denoted by k and the viscosity resistance due to the damping medium is denoted by R, then the following applies to the equation of motion of the quartz plate in the case of a cantilever-like restraint: where 0 is the angular frequency of the mechanical vibration of the moving system including the quartz crystal plate and A is a constant.

Solving equation (4) gives: where: #o and # 1 are the angular frequencies of the mechanical oscillation 0 of the moving system including the oscillating quartz plates for R s 0 and R = O.

In equation (5), the expression in question with regard to the damping medium is the second term, so that if B denotes the amplitude, and also: The relationship between is shown graphically in FIG.

The optimum value of the viscosity resistance R is obtained according to the characteristic curve B in FIG. 6, so that for in the case of the accelerometer according to the invention, R = 14.2 x 10 2 14.7 x 10 2 (dyn sec / cm) results.

The viscosity resistance R is further determined by the shape and dimensions of the weight, since the following applies: R = c6 where C is one of the shape and dimensions of the The constant and the coefficient of dynamic viscosity are determined by the weight.

For the proposed embodiment of the invention, it was determined that a value of = 120 centipoise (1/100 dyn. sec / cm2) to form the value of R is suitable.

Since the coefficient of dynamic viscosity for water is "1", is the coefficient of dynamic viscosity to be used according to the invention 120 times the coefficient of water.

Such a value of the coefficient of dynamic viscosity of 6 = 120 centipoise can easily be achieved by using commercially available silicone oil will.

In addition to liquid substances such as silicone oil, powdery substances can also be used Find material use, as in general any material can be used, that has a dampening effect.

The filling of inert glass in the second cavity within the Bellows 8 is done for a common reason. Through the arrangement of oscillating quartz plates In an atmosphere of inert gas, the aim is to slow down aging, prevent oxidation of the electrode 3, etc., and hence the operational reliability to increase the arrangement.

The reason for using the bellows 8 that allows the weight 9 to to move in the horizontal direction of the two quartz crystal plates 1 and 2, consists in particular in the absorption of the increase in volume due to thermal Expansion of the damping medium.

If an object moves on which measurements are to be made, with a certain acceleration in the direction of arrow A, the moves Accelerometer also with the same acceleration in the direction of the Arrow A. At this point in time, such a force is exerted on the weight 9, that it is in its original position due to its persistence or its indolence remains, and this force acts equally as that in the opposite Load exerted on the two quartz crystal plates 1 and 2 in the direction of arrow A. The first and the second quartz crystal 1 and 2 are bent because they are attached to each other attached free ends in a direction opposite to the direction of arrow A. move.

Therefore, a tensile force acts on the first quartz oscillator plate 1 and a Pressure force on the second quartz oscillator plate 2, and the corresponding resonance frequency changes proportionally to the amount of acceleration, such as the characteristics a and b can be seen in FIG.

As in the present embodiment of the invention, the acceleration due to the beat frequency between the first quartz crystal plate 1 and the second quartz crystal plate 2 is determined, the acceleration is by an approximate two variations of the resonance frequency of an oscillating quartz plate detected.

The acceleration and the on the quartz crystal plate due to the The forces acting on the acceleration are proportional to each other, and those on the quartz crystal plate acting force and the resonance frequency of the quartz plates are also available in proportion to each other so that it is easy to get out of the change derive the amount of acceleration from the resonance frequency.

The following describes the change in the characteristic values of the quartz oscillator plates explained due to temperature changes.

Due to the changes in ambient temperature, practice the basic block 5 and the connecting part 4 forces out the stresses in the first oscillating quartz plate 1 and the second quartz crystal plate 2, so that even if the temperature characteristics the quartz crystal plates themselves are good, their resonance frequency changes. However, since the changes in the resonance frequency of the first quartz crystal plate and the second Quartz crystal plate are essentially the same (the changes in the resonance frequency of the two quartz crystal plates 1 and 2 are ideally exactly the same, with the Arrangement consisting of the mounting plate 5, the connecting element 4 and the two quartz crystal plates 1 and 2, are precisely matched to one another), and the Any change in the beat frequency after mixing is recorded will cancel each other out Changes in the resonance frequency due to temperature changes are mutually exclusive, so that a temperature resistant accelerometer is obtained.

In addition, the oscillating quartz plates can, for example, have so-called AT cuts be, with a simply rotated AT cut (rxl) +35 15 'itself a good one Has resonance frequency / temperature characteristic, but the voltage changes in Dependence on the resonance frequency, i.e. the force sensitivity, a temperature dependence having. Fig. D in Fig. 5 shows such an example in which the change the resonance frequency as a function of temperature changes as a straight line with respect to Changes in temperature.

To measurement errors due to the temperature dependence of this force sensitivity to avoid the thermal expansion of the damping medium according to the invention positively exploited.

This enlarges in the arrangement according to FIG. 2 in the first cavity 18 filled damping medium due to a temperature increase its volume, see above shifts the weight 9 in the direction of the quartz crystal plates 1 and 2, which State is illustrated in Fig. 3.

In Fig. 3 illustrates that shown in solid lines Weight 9 the state before the shift, while that in dashed lines shown weight 9 'illustrates the state after the displacement.

When the weight 9 shifts, the bearing journals 7 slide on the pin-like element 6 and finally take the one with the reference number 7 ' designated position. The distance between the base block 5 and the bearing journals thus changes with a temperature increase from t1 to t2. For the same, on the force exerted on the bearing journals (i.e. the force acting on the bearing journals at the displacement of the weight 9 due to an acceleration is exerted) the tensile force or the compressive force exerted on the two quartz crystals 1 and 2 become smaller due to a rise in temperature. The change will be accordingly the resonance frequency (absolute value) is smaller, as can be seen from the straight line in FIG. 4 is. On the other hand, there is the change in the resonance frequency due to the temperature dependency of the oscillating quartz plates rises in a straight line with a rise in temperature, like the 5, a change is deleted the resonance frequency due to a displacement of the bearing journals and a change the resonance frequency due to the temperature dependence of the oscillating quartz plate mutually, so that the quartz crystal accelerometer according to the invention has a very low temperature dependence.

The volume of the first cavity 18 is taking into account the thermal Expansion coefficient of the damping medium used and the resonance frequency / temperature characteristic (Temperature dependency) of the quartz crystal is determined. In particular, the volume of the first cavity 18 (volume of the damping medium) determined such that the Change in the resonance frequency due to a displacement of the bearing pin 7 to Weight 9, which is due to a change in volume of the damping medium due to a Temperature change caused, as well as the change in the resonance frequency of the oscillating quartz plates themselves cancel or cancel each other out due to a change in temperature.

The straight line labeled c in FIG. 5 illustrates the temperature dependency the force sensitivity of the embodiment of the accelerometer according to the invention, which has good characteristics in a wide temperature range (-200C to + 600C).

As can be seen from the preceding description, the measures Accelerometer according to the invention the acceleration by detecting the beat frequency two oppositely arranged quartz crystals, so that although the quartz crystal or the quartz crystal displacements or deformations on their holding part (e.g. the parts fixed within the base block 5) due to temperature changes are exposed to cancel out the measurement errors based thereon, so that an accelerometer with a good temperature resistance or good Temperature characteristics is obtained. Because of the bellows and the support points or support pin formed movable arrangement results in a more stable, more adaptable Structure, as well as the thermal expansion of the damping medium of a positive one Use is supplied by the voltage exerted on the quartz oscillators being variable is held, whereby the resonance frequency / temperature characteristic curve (temperature dependence) at unit voltages is improved if the quartz oscillators are subjected to stresses so that a quartz crystal accelerometer independent of temperature changes is obtained.

In addition, there is the shifting of the support points or support journals even possible manually, which means that there is a possibility of correction for changing the Resonance frequency as a function of the acceleration of the quartz oscillators, and since a damping medium is present, damage to the quartz crystal will occur because of Medical resonance of the moving system is prevented and one in a short time Acceleration recorded or measured at the zenith is displayed.

According to the invention, there is thus an advantageous quartz oscillator accelerometer or acceleration detector, in which several quartz oscillators are located opposite one another are arranged, with one end of the quartz crystal arranged fixedly and the other End is freely movable, a weight is attached to the free end1 which is a large one Moment of inertia with respect to the acceleration to be measured develops when a Acceleration acts on the weight being exerted and being deflected or shifted this weight due to the associated deviation of the resonance frequency the quartz crystal is used to record or measure this acceleration.

Claims (3)

Claims 1. s chle accelerometer with a quartz oscillator arrangement for a moving object, d u r c h e k e n n n z e i c h -n e t that at least two quartz crystals (1, 2) are firmly connected to one another at their ends are that their major surfaces are opposite to each other and a gap or space is formed between the quartz oscillators (1, 2), the ends of the quartz oscillators fixed on one side in relation to the moving object and on the other Side are movably arranged with respect to the moving object, and that a weight (9) is provided at the movable end of the oscillating crystals (1, 2), wherein the inertial force that occurs when the moving object accelerates, which on the weight (9) in the opposite direction to the direction of acceleration acts to maintain the original state of motion or standstill relative to acceleration maintain, in a beat frequency to the resonance frequency of the two Quartz crystals (1, 2) implemented and the resulting difference for measuring the Acceleration of the moving object is used. 2. Accelerometer according to claim 1, d a d: u r c h g e -k e n n e i n e t that a moving assembly that accelerates a the moving object to be tested is transferred to at least two oscillating crystals (1, 2), is surrounded by damping material. 3. Accelerometer according to claim 1, d a d u r c h g e -k e n n z e i c h n e t that a bellows (8), which in the horizontal direction of the quartz oscillators (1, 2) is expandable and contractible, the two quartz crystals (1, 2) in itself receives and between the fixed end of the quartz crystal (1, 2) and the weight (9) is arranged, and that support points (7) between the weight (9) and the Quartz oscillators (1, 2) arranged displaceably in the expansion direction of the bellows (8) are, wherein the weight (9) and the bellows (8) are surrounded by damping material and the position of the support points (7) on the quartz crystals (1, 2) due to changes in volume due to temperature changes of the damping material are shifted to the Temperature dependence of the force sensitivity with temperature changes of the oscillating crystals (1, 2) to improve.