JP2006184192A - Electronic balance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic balance capable of reducing an error caused by a characteristic of an A/D converter. <P>SOLUTION: This balance is constituted of a load detecting mechanism 3 for balancing electromagnetic force proportional to a coil current I with an on-pan load W; a PID control part 68; a reference resistor 41 for converting the coil current I into a voltage signal; the plurality of A/D converters 42, 43, 44 common in a reference voltage source 46; and a display part 4 having an averaging function, a weight value conversion function and a display function, and stationary errors intrinsic to the A/D converters and fluctuation errors of a temperature and the like are thereby averaged to be reduced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electromagnetic force balance type electronic balance that measures a load by balancing a load applied to a balanced beam and an electromagnetic force across a fulcrum.

  Conventionally, in an electronic balance, an electromagnetic force balance method is used as one of the measurement methods. This is because the electromagnetic force generated in proportion to the current flowing in the force coil provided in the magnetic field of the permanent magnet, the load on the pan, The analog voltage proportional to the current in the balanced state is converted into a digital value using a single AD converter, and then an arithmetic process is performed to measure the load on the plate. FIG. 6 shows a configuration of a conventional electromagnetic balance type electronic balance including a load detection mechanism 101 and a PID control unit 102. The coil current I corresponding to the pan load W applied by the weighing object 2 is a reference resistance. It is converted into a voltage signal by the body 103, and this voltage signal is converted into a digital value by the AD converter 104. This digital value is arithmetically processed by the arithmetic processing unit 105 and converted into a weight value, and is used for the load detection mechanism 101 that greatly affects a measured value difference, that is, a temperature error accompanying a temperature variation from the temperature at the time of calibration. The temperature correction circuit 107 roughly corrects the temperature coefficient of the permanent magnet 108 by using the reference voltage source 106 having a temperature coefficient of about +400 ppm / ° C., and the remaining correction deficiency is corrected by software. .

The coil current I corresponding to the dish load W has a relationship of the following equation (1), where L is the length of the force coil, B is the magnetic flux density, and K is the proportionality coefficient.
I = K · W / (B · L) (1)
As described above, in the prior art, the digital conversion value that is the basis of the weight display value is based on only one AD converter, and the performance of the electronic balance is greatly influenced by the performance of the AD converter itself. .
Japanese Patent Publication No. 7-6830

The conventional electronic balance is configured as described above. However, in the method using a single AD converter, there is a lack of stability of the AD converter as a major factor that hinders improvement in the accuracy of the electronic balance. That is, the main performance of the AD converter, linearity and its temperature coefficient, zero drift and its temperature characteristics, sensitivity (span) stability and its temperature characteristics, fluctuations, etc. hindered the improvement of the accuracy of the electronic balance. Yes.
The present invention has been made in view of such circumstances, and an object thereof is to provide an electronic balance in which the influence of error factors of the AD converter itself is reduced.

In order to achieve the above object, an electronic balance according to the present invention includes a load detection mechanism that detects a load on a pan, an AD converter that A / D converts a load detection signal detected by the load detection mechanism, and the AD balance. In an electronic balance having a display unit for converting and displaying a digital output signal of a converter into a weight value, a plurality of AD converters each having an analog input terminal and a reference voltage input terminal connected in common, and the AD converter A reference voltage source for inputting a reference voltage to a temperature sensor, a temperature sensor for measuring an internal temperature, and an output voltage of the reference voltage source based on a temperature detection signal of the temperature sensor to roughly correct a measurement error caused by a temperature change. A temperature correction circuit to be changed, arithmetic processing means for correcting based on a temperature detection signal of the temperature sensor in order to precisely correct the remaining measurement error, and outputs of the plurality of AD converters It is obtained by an arithmetic processing means for calculating an average value or sum.
Further, the present invention provides three or more AD converters, a reference voltage source for inputting a reference voltage for calibration to the AD converter, a load detection signal input to the AD converter and a reference voltage for calibration for a predetermined time. Switching means for switching each time, correction means for calculating, correcting, and storing output errors of the plurality of AD converters when the calibration reference voltage is input, and an AD converter having the output error larger than a specified value The AD converter selection means which excludes and uses only the remaining AD converter is provided.

Since the electronic balance of the present invention uses a plurality of AD converters to share the input side and averages each digital output to calculate the load, the linearity, zero drift, sensitivity ( Span) and their temperature characteristics and fluctuations are averaged, improving performance error and stability.
Also, by calibrating the AD converter with a built-in reference voltage source for calibration of the AD converter, an AD converter with a large output error and its variation is selected and removed from the operation target, and the remaining AD converter Since the digital output is averaged to calculate the load, sudden error generation can be eliminated.

  Hereinafter, the electronic balance of the present invention will be described in detail by way of examples. FIG. 1 shows a configuration of an electronic balance according to an embodiment. A load detection mechanism 3 for obtaining a current corresponding to a load of a weighing object 2 placed on a weighing pan 1, that is, a load on a pan W, and the current. And a display unit 4 for displaying the weight value of the weighing object 2.

  As shown in FIG. 1, the load detection mechanism 3 has two beam members 52, 53 formed with a thin portion 51 at a predetermined interval so as to be parallel in the vertical direction, and one end side thereof is set to the vertical position of the movable column 54. It is connected and fixed at the other end side to form a Roverval mechanism, and is supported by a load transmitting mechanism portion 5 for transmitting the dish load W in the vertical direction and a fulcrum 61, and one end side is connected via the connecting member 62. A magnetic field generator 66 having a balanced beam 64 coupled to the movable column 54 and having a force coil 63 suspended at the other end, and a permanent magnet 65 for supplying a magnetic field for generating an electromagnetic force to the force coil 63; A position detection sensor 67 for detecting an electric signal proportional to the vertical displacement of the balanced beam 64, and a PID controller for supplying a coil current I for balancing the force coil 63. And a load balancing mechanism 6 consisting of 8.

  The display unit 4 includes a reference resistor 41 connected in series with the force coil 63, and AD converters 42 and 43 that convert a voltage signal generated when the coil current I flows through the reference resistor 41 into a digital value. 44, an arithmetic function for averaging the digital outputs from these AD converters 42, 43 and 44, and an arithmetic processing program for calculating the weight value of the weighing object 2 by multiplying the averaged data by a conversion factor An arithmetic processing unit 45 composed of a memory or CPU for storing, a reference voltage source 46 connected to the AD converters 42, 43, 44, and a permanent magnet 65 of the magnetic field generator 66 is fixed to the reference voltage source 46. A temperature sensor 47 for converting the temperature into an electric signal, and a temperature correction circuit 48 having a temperature characteristic for correcting the temperature characteristic of the permanent magnet 65 in the reference voltage source 46; And a display unit 49 for displaying the weight value data at the arithmetic processing unit 45.

またＡＤ変換器４３、４４の出力データＤＡＴＡ２、ＤＡＴＡ３も（数１）式と同様な関係を有する。これらのＤＡＴＡ１、ＤＡＴＡ２、ＤＡＴＡ３は前記演算処理部４５で（数２）式に示す平均化演算が行なわれＤＡＴＡ４に変換される。

As the AD converters 42, 43, and 44, for example, a high-precision ΣΔ AD converter including an integrator 42a, a comparator 42b, a flip-flop 42c, and a 1-bit DA converter 42d as shown in FIG. 2 is used. . When the output voltage of the DA converter 42d corresponding to the output levels L and H of the flip-flop 42c is + Vref, −Vref and the input voltage is Vin, the output data DATA1 of the AD converter 42 is expressed by the following equation (1).

Also, the output data DATA2 and DATA3 of the AD converters 43 and 44 have the same relationship as that in the equation (1). These DATA 1, DATA 2, and DATA 3 are converted into DATA 4 by the arithmetic processing unit 45 performing the averaging operation shown in the equation (2).

  DATA1, DATA2, and DATA3 in the above equation (2) vary with time due to variations in the characteristics of electronic components such as the offset voltage of the OP amplifier used in each AD converter. As a result, the main performance as an AD converter, that is, linearity and its temperature coefficient, zero drift and its temperature characteristics, sensitivity (span) stability and its temperature coefficient, instability such as fluctuations are averaged and accuracy And stability is improved.

  FIG. 3 shows the configuration of an electronic balance according to another embodiment. The same components as those shown in FIG. The electronic balance has a reference voltage source 7 that can input a reference voltage for calibration to the AD converters 42, 43, and 44 in the electronic balance of FIG. 1 and a control side and a calibration side based on a control signal from the arithmetic processing unit 45. Is provided with a switching device 8 for performing switching. The reference voltage source 7 is internally switched by the arithmetic processing unit 45 so that a reference voltage corresponding to, for example, an input range 0%, 50%, 100% of the AD converters 42, 43, 44 can be generated. A switch 71 is provided.

  4 and 5 are flowcharts showing the measurement procedure of the electronic balance. The method for measuring the present electronic balance will be described below with reference to FIGS. 1, 3, 4, and 5. First, when the power is turned on and started, the switch 8 is switched to the measurement side (point a side), and the dish load W is converted into digital values by the AD converters 42, 43, and 44 (ST1 to ST4). . Each digital value is arithmetically processed on the basis of the respective correction arithmetic expressions calibrated in advance, and read into the arithmetic processing unit 45 as DATA1, 2, 3 (ST5). Then, DATA1, 2, 3 are converted to DATA4 which is an average value of these (ST6). Next, DATA4 is converted into weight data based on the weight conversion formula (ST7) and displayed on the display 49 (ST8). When the number of calculation processes until the display exceeds 5, for example, the AD converters 42, 43, 44 are calibrated (see FIG. 5) (ST9).

  When the calibration is started, the switch 8 is first switched to the calibration side (point b side) (ST10), and the reference voltages corresponding to the measurement ranges 0%, 50%, and 100% from the reference voltage source 7 are sequentially supplied to the AD converter 42. , 43 and 44 and A / D conversion is performed (ST11 to 13). Each data is compared with each reference digital value, and its error is calculated (ST14). The correction calculation formula used in ST5 (FIG. 5) is corrected, and simultaneously with returning to ST1 (FIG. 5), the switch 8 is switched to the measurement side (point a side) (ST16). If the conversion error of the AD converters 42, 43, 44 is larger than the specified value during calibration, the AD converter is excluded (ST17), and the two remaining normal ADs are processed. Averaging is performed using only the converter. As described above, the AD converter has a function of inputting a certain reference voltage, whereby it is possible to verify whether there is a large difference in the digital conversion value of the AD converter. By using the remaining AD converters without using them, it is possible to reduce the influence of the performance of the AD converters that generate sudden errors.

  The electronic balance of the present invention is not limited to the configuration of the embodiment described in detail. For example, an AD converter using another method such as a double integral type or a successive approximation type or the number of continuous measurements can be used. It is also possible to change or use three or more AD converters.

  The present invention is used for an electromagnetic force balance type electronic balance that measures a load by balancing a load applied to a balanced beam and an electromagnetic force across a fulcrum.

It is a block diagram of the electronic balance by an Example. It is a block diagram of the AD converter which concerns on an Example. It is a block diagram of the electronic balance by another Example. It is a flowchart figure explaining the measurement operation of an electronic balance. It is a flowchart figure explaining the calibration operation of an electronic balance. It is a block diagram of the conventional electronic balance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Weighing pan 2 Weighing object 3, 101 Load detection mechanism 4 Display part 5 Load transmission mechanism part 6 Load balance mechanism part 7, 46, 106 Reference voltage source 8 Switching device 41, 103 Reference resistor 42, 43, 44, 104 AD Converter 42a Integrator 42b Comparator 42c Flip-flop 42d DA converter 45, 105 Arithmetic processing unit 47 Temperature sensor 48 Temperature correction circuit 49 Display 51 Thin part 52, 53 Beam member 54 Movable column 61 Support point 62 Connecting member 63 Force coil 64 Balance beam 65, 108 Permanent magnet 66 Magnetic field generator 67 Position detection sensor 68, 102 PID control unit 71 Changeover switch 107 Temperature correction circuit I Coil current W Load on plate

Claims (2)

  A load detection mechanism for detecting the load on the pan, an AD converter for A / D converting the load detection signal detected by the load detection mechanism, and a digital output signal of the AD converter for converting to a weight value and displaying it In an electronic balance equipped with a display unit, a plurality of AD converters each having an analog input terminal and a reference voltage input terminal connected in common, a reference voltage source for inputting a reference voltage to the AD converter, and an internal temperature measurement A temperature correction circuit that changes the output voltage of the reference voltage source based on a temperature detection signal of the temperature sensor in order to roughly correct a measurement error caused by a temperature change, and precisely corrects the remaining measurement error Therefore, arithmetic processing means for correcting based on a temperature detection signal of the temperature sensor and arithmetic processing means for calculating an average value or a total value of the outputs of the plurality of AD converters are provided. Electronic balance, characterized in that is.   Three or more AD converters, a reference voltage source for inputting a calibration reference voltage to the AD converter, and switching means for switching the load detection signal and the calibration reference voltage input to the AD converter at regular intervals And correction means for calculating / correcting / storing output errors of the plurality of AD converters at the time of inputting the calibration reference voltage, and AD converters having the output error larger than a specified value are excluded, and the remaining 2. The electronic balance according to claim 1, further comprising AD converter selection means that uses only an AD converter.

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