RU2576350C1 - Multi-point frequency method of mass and deformations measurement - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: method to measure mass and deformations consists in measurement of parameters of strain gauges, which are arranged in reference points in the area or the section of the investigated object. At the same time they measure the frequency of the generator formed by strain gauges connected to external capacitors of the phasing RC-circuit and the amplifier. The averaged signal of the generator is sent via a functional frequency-code converter to a digital indicator. Frequency of the generator depends on parameters of strain gauges. The stated invention makes it possible by a frequency method to continuously measure mass and deformation of the object using a double-wire line of communication and identical standard strain gauges (strain sensors) with averaging of readings without additional computing operations.

EFFECT: high reliability and noise immunity of the method, such method eliminates influence of instability of metering circuit power supply voltage, subsidence, inclination of a foundation and platform of scales, displacement of a centre of masses of weights by measurement error.

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Description

The invention relates to the field of electronic weighing equipment and can be used in various industries and vehicles for fast and high-precision determination of the mass of a vehicle with bulk and liquid cargo when loading or unloading, moving goods of various kinds by lifting mechanisms and at the same time weighing them, for example, crane monorail and other scales, measuring forces and pressures, as well as to study the physical properties of materials, deformations and stresses in parts and instructions.

A known method of measuring weight and strain using from one to four strain gauges in the measuring circuit in the form of balancing bridges or quasi-balancing (Levshina ES, Novitsky PV Electrical measurements of physical quantities. - L .: Energoatomizdat. 1983. - S. 102-107).

The disadvantages of this method of measurement are the low level of the amplitude output signal of not more than 10-50 mV, which complicates remote measurements, the complexity of the circuit in the case of simultaneous measurement at many points of an extended object.

A device is known that implements the multi-support weighing method (RF patent No. 121570, G01L 25/00, publ. 10/27/2012), in which multicomponent strain gages are placed, each of which contains a main bridge of strain gages for measuring force and two additional bridge of strain gages, measuring the moments of forces applied to their power leading and supporting nodes on a standard power reproducing installation, and judge the measured weight by the sum of the signals of the main bridges of the strain gages of all sensors, while monitoring the signals strain gauge bridge-negative. Measuring the signals of additional strain gages bridges allows you to control the correct orientation of multicomponent weight sensors on a reference force-reproducing machine.

The disadvantages of using this device and the method it implements are the low power of the output signal and the effect of subtle destabilizing factors (subsidence and inclination of the foundation and platform) on the measurement error.

A known method of multi-support weighing (RF patent No. 2518097, G01G 1/00, publ. 06/10/2014), consisting in the fact that the multi-component strain gauge weight sensors, each of which contains the main bridge of strain gages, designed to measure weight, are loaded on a reference force reproducing installation, and additional strain gauge bridges designed to measure mechanical influencing quantities. Under this loading, the signals of the main and additional bridges of the strain gages of each weight sensor are measured, the conversion characteristics of the main and additional bridges of the strain gages are determined, for each multicomponent strain gage of the weight sensor, the functions of the influence of the signals of the additional bridges of the strain gages on the error in the conversion of the main bridge of the strain gages and the maximum allowable signal values of the additional bridges are determined strain gages for which the error of the signal of the main bridge The resistance of this multicomponent strain gage weight sensor does not go beyond the permissible limits. On-site operation, the measured weight is judged by the sum of the signals of the main bridges of the strain gages of all multicomponent strain gages of the weight under a predetermined condition for the maximum permissible signal value of the additional bridge of the strain gages, in which the error in the signal of the main bridge of the strain gages of this multicomponent strain gage does not exceed the permissible limits.

The disadvantage of this method is the use of a large number of additional multicomponent strain gauge sensors and strain gauge bridges, as well as the low power of the output informative signal.

A known method of weighing on a wagon electronic scale to assess the safety of movement of wagons with bulk cargo (RF patent No. 230084, G01G 19/04, dated 15.12.2005, publ. 27.05.2007). The method consists in weighing a moving car, taking into account the gross mass measurement of the left and right sides of the car. By summing, the gross weight of the wagon is determined. The measurement of the mass difference of the loading of the sides of the car is obtained as the sum of the corresponding differences of the two carriages on the left and right sides. Additionally determined by calculation by the limit value of the transverse displacement of the center of mass of the load "a" from the longitudinal axis, the same gross masses distributed on the left and right sides of the two wagon trolleys. Then, the mass difference in the loading of the sides of the wagon is calculated by subtracting from the gross mass distributed on the left side of the two bogies, the gross mass distributed on the right side of the two bogies. The calculated mass difference between the loading masses of the left and right sides of the car is compared with the mass difference measured on the balance.

The disadvantage of this method is the use of a large number of bridges of strain gages, low power output of the informative signal and the need for manual calculations.

There is also a method of using chain circuits with semiconductor strain gauges to increase the level of the amplitude informative signal (Rakhmanov V.F., Trukhachev B.S. Chain circuits with strain gauges // Measuring equipment. - 1970. - No. 9. - P. 52-54; Dragunov V.P. Analysis of the characteristics of multi-element strain transducers // Electronic Instrument Making. Novosibirsk, NETI. - 1992. - P. 131-139).

The disadvantages of this method are the limited scope of using circuitry from strain gages only in local measurement zones, low noise immunity of the amplitude informative signal and the difficulty of averaging the measurement results.

The closest in technical essence is the method of converting the strain gage imbalance to the pulse frequency using an integrator on an operational amplifier and a comparator, depending on the change in the resistance of the strain gage, implemented in the converter of the strain gage unbalance signal to the output frequency f (AS USSR No. 828406, MKI H03K 13 / 20, publ. 07.05.81. Bull. No. 17), which is determined by the formula

where ε _R is the relative change in the resistance of the strain bridge from the effects of the measured pressure;

R _And - the resistance of the integrator, which includes the output resistance of the strain gauge bridge and the resistance of the cable line;

With _D is the capacity of the metering capacitor.

The disadvantages of the method implemented by the device containing the strain gauge pressure sensor and the frequency converter of the signal from the output of the strain gauge bridge are low accuracy when the resistance of the strain gages changes with the temperature of the heating of the strain gage and the converter operates only when the strain gage is unbalanced in one direction, and at zero imbalance the output frequency of the converter is to zero.

The objective of the invention is the measurement of mass and deformations both on small and large areas and extended sections of the studied objects using the required number of strain gages, averaging readings without additional computing devices, eliminating the influence of instability of the supply voltage of the measuring circuit, drawdown, slope of the foundation and platform scales as well as the displacement of the center of mass of the cargo by measurement error, increasing the noise immunity of the informative signal from the possibility of its remote transmission over a two-wire communication line.

The technical result is averaging the frequency without additional computing devices, eliminating the influence of instability of the supply voltage on the output frequency and the need to increase the supply voltage of the strain gauges to increase the level of the output signal, causing additional errors from their heating.

The problem is solved by the method of measuring mass and strain by measuring the frequency of the generator, which depends on the parameters of the strain gages, which according to the invention are located at control points over the area or area of the test object and connected to external capacitors of the phasing RC circuit, forming together with the amplifier a generator connected via a functional frequency-code converter with digital display.

The essence of the method is illustrated by drawings, where:

- in FIG. 1 shows a chain structure converter;

- in FIG. 2 is a schematic diagram of a phasing chain;

- in FIG. 3 is a schematic diagram of a phasing chain with one strain gauge;

- in FIG. 4 is a measurement diagram using strain gages as elements of a phasing chain of an RC generator.

The method is implemented using strain gages located at control points along the object and forming, together with external capacitors, a phasing RC chain of a harmonic oscillation generator, the frequency of which depends on the mass or deformation of the object.

Known traditional research methods do not allow obtaining analytical expressions that relate the measured parameter to the generation frequency, which depends on the simultaneous individual change of the parameters of several (more than four) strain gages, and thereby solve the actual problem.

Using the method of transformation functions (FP) allowed us to effectively solve this complex problem (see Gulin A.I. Diagnostics of measuring transducers and communication devices with an inhomogeneous chain structure // Control. Diagnostics. 2010. No. 11. P. 69-72).

FP K _{n of the} converter of the chain structure (Fig. 1) (formally, the reciprocal of the traditional transfer coefficient), which is the ratio of the input active quantity U ₀ to the output B _n (voltage U _n or current I _n ), is described by the expression for an even number of arms n

where i = 2b-1;

b = 1, 2, 3, ..., 0.5n,

and for chain structures (CS) with an odd number of shoulders n

where b = 1, 2, 3, ..., 0.5 (n + 1) for a CA with an odd number of shoulders n.

Relations (1) and (2) lead to a recurrence formula for calculating the phase transition

where T _{i is the} immitance of the ith shoulder (resistance Z for odd i and conductivity Y for even i).

The initial conditions of the calculation algorithm K _n are the values K ₀ = 1 for n = 0 and K ₁ = T ₁ for n = 1.

The recommended circuitry of the RC phasing chain (FC) is shown in FIG. 2. Therefore, the required minimum number of strain gages to create a FC should be at least two. The article (see Gulin A.I. Designing multi-link RC generators // Izv. Universities "Instrument Making" 2012. V. 15. No. 1 (41). P. 14-118) presents all sorts of FC schemes that can be used for constructing various schemes of measuring generators With large areas and extended sections of the controlled object, the number of strain gages is increased to the required number (several hundred), placing them at the necessary control points. Consider, as an example, a six-arm FC consisting of three capacitors and three strain gauges.

The expression of the AF of the six-armed FC according to (1) will be

For FC (Fig. 2), when Z ₁ = Z ₃ = Z ₅ = 1 / jωС, and Y ₂ = Y ₄ = Y ₆ = 1 / R, the FP will be equal to

In the components of the real and imaginary parts, the phase transition has the form

K ₆ = ₆ + ImK ReK _6,

The condition for oscillations when using FC is

where K _AP - FP active converter (amplifier);

K _FC - FP phasing chain.

Because OP amplifier is real, then the condition (6) requires that FP CA K _FC on self-excitation frequency was too real. In this case, both phase transitions can simultaneously have either positive or negative values, i.e. FC, depending on the type of active converter, must carry out a phase shift by an even or odd number πi radians, where i = 1, 2, 3 ... is a natural series of numbers.

Consider the question of determining the frequency of the quasi-resonance of the six-arm FC (Fig. 2), composed of strain gauges with resistance P and capacitors with a capacitance C that rotates the phase by 180 °, which is most often used when constructing generators with single-stage amplifiers. The frequency of the quasi-resonance is determined from the imaginary part of the phase transition phasing quadripole (FC) when it vanishes, i.e.

Equating the imaginary part of the phase transition (quasi-resonance condition) of expression (5) to zero, we obtain the formula for the desired frequency ω _{0 of the} six-arm FC

where from

We determine the real part of the phase transition ReK ₆ FC at the frequency of quasi-resonance ω ₀ from expression (5)

a, substituting the value of the frequency of quasi-resonance from (8), we define

ReK ₆ = -29.

FC attenuates the signal level by 29 times, and a minus sign confirms a phase rotation of 180 °. Therefore, K _AP - AF of the active transducer (gain) should exceed more than 29 times.

It should be noted that the phase transition K _n FC at the frequencies of quasi-resonance with increasing number of arms n from six to infinity decreases and tends from K ₆ = -29 to Kn = -11.6, i.e.

Calculations for calculating the frequencies of quasi-resonances for an arbitrary number of strain gauges n / 2 are reduced, as it turned out, to determining the coefficient k _{n of the} expression

As a result of analytical analysis, a formula was first obtained that determines the coefficient k _n for the FC for any number of strain gages from equations of the form

where p = 0.25n-1 - for even 0.5n;

p = 0.25 (n + 2) -1 - for odd 0.5n.

For example, for ten-arm (five-link) FC equation (9) has the form 15k-28k ³ + k ⁵ = 0, the solution of which gives the following values of k:

k _1,2 = ± 23/32; k _3.4 = ± 167/32; k ₅ = 0.

Of all the real positive roots of equation (9), it is necessary to use the smallest value k = 23/32, since the use of other values satisfying (9) will lead to a phase shift of 2π radians or more.

When it is necessary to use one or two strain gauges, a five-arm FC is used (Fig. 3). The frequency of quasi-resonance of a similar FC consisting of an odd number of shoulders is determined by the expression

where the coefficient h _n also depends on the number of arms of the FC and is determined from the equation

- число сочетаний из 0,5(n+1)+2i элементов по 1+4i элемента;Where

- the number of combinations of 0.5 (n + 1) + 2i elements of 1 + 4i elements;

m = 0.25 (n + 1) -1 - for even 0.5 (n + 1);

m = 0.25 (n-1) - for odd 0.5 (n + 1).

, а частота квазирезонанса ω₀ будет равнаFor five-arm FC coefficient $$h_5=\sqrt{3}$$

, and the frequency of quasi-resonance ω ₀ will be equal to

If it is necessary to use only one strain gage in the FC, replace one of the strain gages P with an active resistance R (Fig. 3). Then the frequency of quasi-resonance is described by the expression

To calculate more complex FCs, you can use the program (see, Gulin A.I., Sukhinets Zh.A. et al. Calculation of the quasi-resonance frequency and transmission coefficient of multi-link RC structures // Certificate of official registration of a computer program No. 2003611147 / 16.05. 2003. Rospatent. Moscow. 2003).

A multi-point frequency method for measuring mass and strains with fast averaging of readings (Fig. 4) on an extended object or a large-area object contains strain gages 1, constituting elements of the phasing chain 2 with external capacitors to form an amplifier 4 together with amplifier 3, connected through an functional frequency converter code 5 with a digital indicator 6.

The measurement of mass or deformation at the object is as follows. The same type of strain gages (strain gauges) 1 are placed at the controlled points of the object, connected to external capacitors to form a phasing chain 2, which together with amplifier 3 generates 4, which are connected through a frequency-code converter 5 to a digital indicator 6. When the mass and deformations of the controlled of the object changes the resistance values of the strain gauges forming the phasing chain 2 of the generator 4. In accordance with the values of these resistances, the frequency of the generator and 4, which is converted by a functional frequency-code converter 5 and displayed on the digital indicator 6 in the appropriate units.

So, the claimed invention allows a frequency method to continuously measure the mass and deformation of an object using a two-wire communication line and the same standard strain gages (strain gauges) with averaging readings without additional computational operations, which ensures high reliability and noise immunity of the method.

In addition, this method eliminates the influence of instability of the supply voltage of the measuring circuit, subsidence, the slope of the foundation and platform of the scale, as well as the displacement of the center of mass of the cargo on the measurement error, when the platform, sections of the rail track are tilted or the center of mass of the load is shifted, an increase in the resistance of some strain gages will correspond to a decrease in the resistance of the others, while the output frequency of the generator, and therefore the measurement result, will not change.

Claims (1)

A method of measuring mass and strain by measuring the frequency of the generator, depending on the strain gauge parameter, characterized in that the strain gauges are located at control points over the area or area of the test object and connected to external capacitors of the phasing RC circuit, forming together with the amplifier a generator, the average signal of which is supplied through a functional frequency-code converter to a digital indicator.

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