SU1631305A1 - Digital electromagnetic balance - Google Patents

Abstract

The invention relates to weighing technology and allows for improved measurement accuracy. Under the action of the load 3, the sensitive element 1 moves and the noncompensation converter 7 produces a signal, which enters the amplifier 17 and further to the input of the pulse-width current regulator 15, which through the isolating amplifiers 20 and 21 increases (decreases) the current in the coil 10 and simultaneously decreases (increases) the current in coil 11 until sensing element 1 returns to its original position. The control signals of the pulse-width control current 15, supplied to the key 41, provide the passage of counting pulses from the generator 42 to the counter 43 in an amount proportional to the time when there is a difference in the currents in the coils 10 and 11. The third balancing coil 12 and scaling and thermocompensating resistors 35 and 36 provide a stable amount of current creating an initial power balance. 2 Il.

Description

This invention relates to a weight measuring technique.

The purpose of the invention is to improve accuracy.

FIG. 1 shows a scale chart; in fig. 2 is a diagram of currents flowing in the coils of the compensator.

The scales contain a sensing element 1 with a load bearing platform 2 for the measured load 3, installed through the supporting device 4 on the base 5, equipped with a flag 5 of the non-compensation converter 7 and a compensator 8 with a magnetic system 9, two counter-balanced coils 10 and 11 as well as the third balancing coil 12 fixed together with the coils 10 and

11, and the calibration weight 13 on the sensitive element 1.

The automatic balancing system 14 contains a pulse width current regulator 15, for example, of an integrating type, connected via input 16 through an amplifier 17, for example, also an integrating type, to a non-compensation converter 7, and through outputs 18 and 19 through isolating amplifiers 20 and 21 - to counter balancing coils 10 and 11, with the outputs 22 and 23 of the amplifying amplifiers 20 and 21 interconnected and connected to the end 24 of the third balancing coil 12, and the outputs 25 and 26 of the converting amplifiers 20 and 21 are connected to the ends 27 and 28 shows but-balancing coils 10 and

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11. In turn, the ends 29 and 30 of the coils 10 and 11 are connected to the outputs 31 and 32 of the coupling amplifiers 20 and 21 and through the reference resistors 33 and 34 (with resistance RI and Ra) to each other, and also connected via scaling and thermocompensating resistors 35 and 36 (with resistances Nz and RT with opposite temperature coefficient a relative to temperature coefficient of coil 12) to zero bus 37 of bias voltage source 38 (value ± VCM). At the same time, the end 39 of the third trimming coil 12 is connected to pole 40 (for example, with the selected winding direction, to the positive pole, + VCM) of the bias source 38. In addition, in the automatic balancing system 14 there is a key 41 connected to the outputs 18 and 19 pulse-width current regulator 15 and installed between serially connected counting pulse generator 42, accumulative counter 43 and indicator 44, for example, for 5-6 digital decades, and also a parallel correction device 45, for example, by the first and the second derivative, connected via its input 46 to the amplifier 17, and through its outputs 47 and 48 to the inputs 49 and 50 of the distribution amplifiers 20 and 21. The inputs 51 and 52 of the latter are connected respectively to the outputs 18 and 19 of the pulse-width control torus current 15. Button 53 serves to reset the counter 43 and indicator 44 when calibrating the zero point of the scale.

Digital electromagnetic scales work as follows.

In the initial position (static), the sensitive element 1 together with the load-receiving platform 2 and when applied to the last load 3 equal to half of the measured load Pmax is balanced by counter-directed identical electromagnetic forces FI and Fa formed by the action of equal currents 11 and i (Fig. 1 and Fig. 2), flowing in counter-balancing coils 10 and 11, as well as the electromagnetic force Fo, formed by the action of the current lo, equal to the sum of the currents H and 12, 0 h + 2 - canst, flowing through the third balancing coil 12, and

c - if i - D o. Rmax

go - Ivolo - go t,

where Co is the coefficient of power conversion of the compensator 8 (coil 12);

Ro is the weight of the sensitive element 1 together with the cup 2, the coils 10, 11 and 12 and the circulating weight 13;

Pmax is the maximum weight of the measured load 3 on the scales.

Additionally, the initial balancing of the sensing element 1 is also carried out by the selection of the calibration weight 13.

Thus, in the initial position, the sensitive element 1 is in equilibrium and its deviation D N by the flag 6 is zero, D N 0. At the same time, the output signal from the non-compensation converter 7

is also 0, 0.

p Then load 3, equal in weight

removed from pad 2, and the indicator 44 is set to 0 by resetting the information in counter 43 by pressing button 53 (Reset). Scales, therefore, prepared for work.

When a measured weight 3 is applied with a weight Px, the sensitive element 1 moves upwards by + YN, if

p weight Px less than or down

on -DH, if its weight Px is greater than the value of Pm2ax

In this case, a signal D VBx arises in the noncompensation converter 7, which enters the amplifier 17 and then to the input 16 of the pulse-width current regulator 15, which, through isolating amplifiers 20 and 21, for example, increases the current h in one of the coils 10 and decreases current 2 in the other coil 11 until, under the action of the difference of the electromagnetic forces FI - F2 created by counter-balancing coils 10 and 11, the sensitive element 1 returns to its original balanced position:

Px Fi-F2 Ki (li-l2)

where K1 is the power conversion coefficient of the compensator 8 (coils 10 and 11).

From the outputs 47 and 48 of the parallel correction device 45 to decoupling amplifiers 20 and 21, signals in opposite phases are proportional to the speed and acceleration of movement ± D N of the moving sensing element 1.

The signals from the outputs 18 and 19 of the pulse-width current regulator 15 entering the key 41 respectively open and close the path of the counting pulses from the generator of counting pulses 42 going to the counter 43, which in turn transmits the indications of the total number of pulses to the indicator 44. As a result, the indicator: 44 receives the sum of NP

impulses, proportional to the difference in the duration (in time) of the currents And and 2, is proportional, in turn, to the weight Px of the measured load 3:

(H-12) КзД1 К4Рх, (4)

where Ks and K4 are scale factors.

The presence of the scaling and thermo-compensating resistors 35 and 36, connected in series with the current 0 to the third balancing coil 12, allows for the choice of the magnitude of the temperature dependence of the resistance a, which are opposite in sign to the coefficients. and "m of resistor 36 and coil 12 improve the stability of fixing the current lo, which creates the initial force balancing of the sensing element 1.

In addition, the use of a balanced principle of building a power balancing system by connecting two counter-balancing coils 10 and 11 to the output circuits of symmetric switching amplifiers 20 and 21, and the third balancing coil 12 to a common point between symmetrical outputs 22 and 23 of the coupling amplifiers 10 and 11, and through the bias source 38 to the zero bus 37 of the indicated source and to the symmetrical point between the reference resistors 33 and 34, eliminates the effect of instability of the output circuits of the pulse-width current regulator 15.

At the same time, the temperature in the magnetic gap of the compensator 8 is stabilized, since the arithmetic sum of the currents h + l2 const of the windings 10 and 11, as well as the current of 10 const in the winding 12 is constant, and the amount of heat generated in these windings is also There are constant values.

Finally, the presence of two identical coils 10 and 11 with counter-balancing on electromagnetic forces FI and F2 makes it possible to achieve the same quality of the balancing processes, both at the position of the measured load 3 and when it is removed, i.e.

Claims (1)

compensator 8 by balancing the effects of demagnetization and magnetizing its magnetic system with 9 currents And and 2, the invention Digital electromagnetic scales containing a sensitive element fixed to the base by means of flexible supports with a load-receiving platform and a non-compensation converter, the output of which is connected via an amplifier to the inputs of a parallel correction node and a pulse-width current regulator whose outputs are connected to the first inputs of the first and second amplifiers and to the control inputs of the key, through which the counting pulse generator is connected to the pulse counter, to the output of which the indicator is connected, the second inputs of the first and second converters the amplifiers are connected to the outputs of the parallel correction node, and the first outputs of the first and second isolating amplifiers are connected to one ends attached to the sensing element the first and second coils of the electromagnetic compensator, the second ends of the coils are connected to one of the terminals of the reference resistors and the third inputs, respectively, of the first and second converters amplifiers, characterized in that, in order to increase accuracy, they introduced a third electromagnetic compensator coil, a bias voltage source, scaling and temperature compensating resistors, the third coil being rigidly fixed on the sensitive element together with the first and second coils and connected at one end to one voltage source pole displacement, and the other end to the second outputs of the first and second decoupling amplifiers, the scaling and temperature compensating resistors connected in series and connected to the other pole of the bias voltage source and to other terminals of the reference resistors.