RU2050528C1 - Electronic weighing machine - Google Patents

Abstract

FIELD: mass measuring technique. SUBSTANCE: weighing machine includes a cargo receiving platform, acting through a loading device upon a strain gage pickup, whose first and second inputs are connected with first and second outputs of sine signal generator. A measuring diagonal of strain gage pickup bridge circuit is connected through a measuring transformer with inputs of a measuring amplifier, whose output is joined with a first input of a phase detector. A second input of the phase detector is connected with a third output of the sine signal generator. The machine also has connected in series a follower, a voltage divider, a high frequency filter, a differential amplifier, an integrator and an analog-to-digital converter, whose output is connected through input-output ports with inputs and outputs of a microcomputer. An output of the phase detector is joined with an input of the follower and with the second input of the differential amplifier. EFFECT: enhanced accuracy of weighing machine. 1 cl, 4 dwg

Description

 The invention relates to a weight measuring technique, in particular to automobile and commercial scales.

 A weight measuring device with vibration compensation [1] is known comprising a load receiving platform, a first sensor, a loading device that transmits force from the load receiving platform through a loading device to a first sensor, a processing unit, an adjustment circuit, and a second auxiliary sensor mounted next to the first sensor and the receiving the effect of floor vibration.

 Weighting device operates as follows.

 The output signal of the first sensor, which includes a DC signal and an interference signal associated with the influence of floor vibration, is fed to the input of the correction circuit, the other input of which receives the signal of the second auxiliary sensor containing the frequency of floor vibration. Next, using the correction circuit, the correction signal is subtracted from the output signal of the first sensor.

 The working signal thus obtained is fed to the input of the processing unit for subsequent processing.

 The disadvantage of this weighing device is the incomplete compensation of interference signals, affecting in general the load platform; feeding sensors with direct current reduces the sensitivity and accuracy of the weighing device.

 Known scales (see ed. St. N 1559255, class G 01 G 9/00) containing an analog-to-digital converter (ADC), a load receiving platform, a sensor and a loading device that transmit force from the load receiving platform through the loading device to the sensor , correction scheme and processing unit.

 Scales work as follows.

 When setting a test load (the highest weighing limit), the ADC sets the exact value (scale) and then sets the other test load (the smallest weighing limit) to zero the ADC, after which the load receiving platform is unloaded, and the reading will be greater than zero. The correction scheme by changing the sensor power sets the reading value to zero using the processing unit.

 Further, the scales weigh the weight that is installed on the load platform, taking into account the adjusted zero and scale.

 The disadvantage of these scales is the lack of compensation for interference affecting the load-receiving platform in general; DC sensor power supply, reducing the sensitivity of the balance and its accuracy.

 The closest in technical essence to the present invention are electronic scales [2] containing a microcomputer, the inputs and outputs of which are connected via input and output ports to the outputs of an analog-to-digital converter, a low-pass filter, a load receiving platform, a strain gauge, the first and second inputs of the bridge are connected with the first and second outputs of the sinusoidal signal generator, and the measuring diagonal of the strain gauge bridge is connected through the measuring transformer to the outputs of the measuring amplifier I, whose output is connected to the first input of the phase detector, the second input of which is connected to the third output of the sine wave generator.

 Electronic scales work as follows.

 When loading the load receiving platform through the loading device, the weight value is transferred to the strain gauge, the first and second inputs of the strain gauge bridge with the first and second outputs of the sinusoidal signal generator, and the measuring diagonal of the strain gauge bridge is connected through the measuring transformer to the inputs of the measuring amplifier and then to the input of the phase detector . After detection by a low-pass filter (digital filter), the carrier value is allocated, which is fed to the input of the analog-to-digital converter. The analog-to-digital converter transmits the received carrier values through the input-output ports to the microcomputer (storage device). During processing, samples are used to obtain a signal proportional to the average value of the processed values.

 A device is connected to the filter, which allows you to manually set the desired filtering level. The measured weight value is displayed on the balance indicator.

 The disadvantage of these electronic scales is the lack of compensatory interference affecting the load-receiving platform and the sensor as a whole.

 The aim of the invention is to improve the accuracy of electronic scales.

 The goal is achieved in that the electronic balance contains a microcomputer, the inputs and outputs of which are connected through the input-output ports to the outputs of the analog-to-digital converter, a load receiving platform, a strain gauge and a loading device that transmits force from the load receiving platform through the loading device to the strain gauge, first and the second inputs of the bridge of the strain gauge are connected to the first and second outputs of the sinusoidal signal generator, and the measuring diagonal of the bridge of the strain gauge dates The IC is connected through the measuring transformer to the inputs of the measuring amplifier, the output of which is connected to the first input of the phase detector, the second input of which is connected to the third output of the sinusoidal signal generator, a repeater, a voltage divider, a high-pass filter, a differential amplifier, an integrator connected in series, while the output a phase detector is connected to the input of the repeater and to the second input of the differential amplifier, the output of the integrator is connected to the input of the analog-to-digital converter spruce up.

 To prove the conformity of the proposed technical solution to the criterion of "significant differences" we define in which technical solutions there are signs similar to those that distinguish the claimed technical solution from the prototype. Distinctive features of the proposed electronic scales are the repeater, voltage divider, high-pass filter, differential amplifier, integrator.

 The listed devices are widely used in technical solutions for their intended purpose (see V. Gutninov, Integrated Electronics in Measuring Devices. L. Energia, 1980). The combination of the serial output of the phase detector and the inverting input of the differential amplifier, as well as the connection of the serial output of the phase detector, repeater, voltage divider, high-pass filter and non-inverting input of the differential amplifier allows the corresponding signals obtained at the inputs of the differential amplifier with high speed to be summed. The use of a phase detector for its intended purpose allows the detection of signals with very minimal levels of information signal measurement (see Horowitz. Hill. W. The Art of Circuit Engineering. M. Mir, 1984, v.2, p. 383).

 The use of an integrator with an analog-to-digital converter connected to the input allows you to remove ripple and noise at the input of the analog-to-digital converter, while maintaining high speed.

 The listed interconnections allow improving the accuracy of electronic scales by isolating the signal by detecting and compensating for an interference signal exceeding the frequency of the working signal, using high speed, the proposed interconnections also due to the processing algorithm on the microcomputer make it possible to use signal extraction by algorithms more complicated than a simple average value. The presence of such new properties allows us to conclude that the proposed technical solution has significant differences.

 In FIG. 1 shows a block diagram of an electronic balance; in FIG. 2 circuit repeater, voltage divider, high-pass filter, differential amplifier and integrator; in FIG. 3 cyclogram of the operation of the repeater, voltage divider, high-pass filter, differential amplifier and integrator; in FIG. 4 algorithm of electronic scales.

 The electronic balance contains a microcomputer 1, input / output ports 2, an analog-to-digital converter 3, a load receiving platform 4, a load device 5 that transmits force from the load receiving platform 4 to a strain gauge 6 having strain gages included in the strain gauge bridge 7, which is connected to the first and second outputs of the sinusoidal signal generator 8, and the measuring diagonal of the bridge of the strain gauge 7 is connected through the measuring transformer 9 to the inputs of the measuring amplifier 10, the output of which is is dined with the first input of the phase detector 11, the second input of which is connected to the third output of the sinusoidal signal generator 8, the voltage follower 12, the voltage divider 13, the high-pass filter 14, the differential amplifier 15 and the integrator 15 are connected in series, and to the second (inverse) input of the differential the amplifier 15 is connected to the output of the phase detector 11, and the output of the integrator 16 is connected to the input of the analog-to-digital Converter 3.

 The sinusoidal signal generator 8 comprises a quartz oscillator 17, the output of which is connected to a low-pass filter 18, the output of the low-pass filter 18 is connected to the third output of the sinusoidal signal generator 8 and the input of the power amplifier 19, the outputs of which are connected to the first and second outputs of the sinusoidal signal generator 8.

 The microcomputer 1 contains a central processor 20, RAM 21, ROM 22, a control panel 23, an indication unit 24, a timer 25, a print unit 25 interconnected via an internal interface including a control bus 27, a data bus 28, an address bus 29, and corresponding ports input-output

 Electronic scales work as follows.

 In the initial state, the load receiving platform 4 immerses the strain gauge 6 through the loading device 5. This load value of the strain gauge 6 should correspond to a zero weight value. After turning on the power (see Fig. 4), all variables and constant I / O ports are initialized and RAM 21 and ROM 22 are tested.

 At the end of the initialization, an appeal is made in the print unit 26, which imprints (the header) the heading "Electronic scales". Then there is a hint through the block display 24 "Number 9", set the number, then there is a hint through the block 24 display "Month". The current month is set, while the display unit gives the prompt "Year". The operator sets the current year and the current time, counted by the timer 25. Each transition is carried out through the "VK" key of the control panel 23.

 After the introduction of the necessary details, the microcomputer 1 proceeds to the "Warm-up" subroutine, which lasts for 10 minutes. After 10 minutes, the display unit 24 issues a prompt "Mode". To compensate for the load value of the strain gauge 6 by the weight of the lifting platform 4, it is necessary to enable the "Correction" K = "mode. In this case, the variable frequency signal from the sinusoidal signal generator 8 feeds the bridge of the strain gauge.

 Strain gauge 6 perceives the initial load and the imbalance signal of the strain gauge bridge 7 in the form of an amplitude-modulated signal, is fed to the input of the measuring transformer 9 and then to the input of the measuring amplifier 10.

 After amplification by the measuring amplifier 10, the amplitude-modulated signal is fed to the input of the phase detector 11, to the other input of which the reference signal from the sinusoidal signal generator 8 is supplied. From the output of the phase detector 11, the demodulated signal (see Fig. 3a) is supplied to the voltage follower 12, which is necessary for decoupling from the voltage divider 13 and the output of the phase detector 11, as well as to the inverse input of the differential amplifier 14, to the other input of which the signal from high pass filter 13 (see FIG. 8b). The cutoff frequency of the high-pass filter 13 is calculated based on the requirements of the non-passage of the working range of the low-frequency envelope of the working signal.

 Thus, if the range of the low-frequency working signal lies in the range, for example, 0-10 Hz, then the cut-off frequency of the high-pass filter should be 10 Hz, in addition, the filter has a certain phase shift at the carrier frequency. As the simplest high-pass filter 14 in the proposed circuit, a capacitance and a resistor are used (see Fig. 2).

 After passing through, the low-frequency noise signals (envelopes) that have passed through the high-pass filter are added in antiphase with the working signal (see Fig. 3c), in which all working and noise signals are present, subtraction occurs and, thus, we obtain a low-frequency envelope with minimal pulsations (Fig. 3b) without the presence of noise accompanying low-frequency components in the envelope. Then, from the output, the signal goes to the input of the integrator 16, which removes the signal ripple, and supplies the original signal to the input of the analog-to-digital converter 3. The values of the analog-to-digital converter 3 are sampled through the input / output ports of the microcomputer 1 and processed accordingly.

 On the block 24 of the indication information is provided about loading the strain gauge sensor 6 in the initial state. This value of the microcomputer 1 is stored in RAM 21, and with subsequent weighings this value is zero, i.e. source.

 After the end of the "Correction" mode, the display unit 24 indicates the initial zero. Electronic scales are ready for weighing. When loading electronic scales with a certain weight value, the "Scales" mode is set. In this mode, the processes described above in the "Correction" mode occur, and the analog-to-digital Converter 3 produces the values corresponding to this weight value.

 The microcomputer 1 processes the values received through the input / output port 2 in accordance with the algorithm and displays the weighted weight value by the display unit 24.

 Compared with the prototype, electronic scales have increased accuracy due to compensation of interference exceeding the frequency of the working signal.

Claims (1)

 ELECTRONIC SCALES containing a microcomputer, the inputs and outputs of which are connected through the input-output ports to the outputs of the analog-to-digital converter, a lifting platform, a strain gauge and a loading device that transmits force from the load receiving platform to the strain gauge, the first and second inputs of the bridge of the strain gauge are connected with the first and second outputs of the sinusoidal signal generator, and the measuring diagonal of the strain gauge bridge is connected through a measuring transformer to the inputs of the measuring amplifier, the output of which is connected to the first input of the phase detector, the second input of which is connected to the third output of the sinusoidal signal generator, characterized in that they include a follower, voltage divider, high-pass filter, differential amplifier, integrator connected in series, the output of the phase detector is connected to the input of the repeater and to the second input of the differential amplifier, the output of the integrator is connected to the input of the analog-to-digital converter.

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