JPH0583847B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an electronic balance, and more specifically, it has two measuring sections, a rough measuring section and a fine measuring section, and a This invention relates to an electronic balance that uses a method to determine weighing values.

<Prior Art> In electronic balances, the sensitivity generally changes with temperature changes due to temperature coefficients of constituent members. The change in sensitivity due to this temperature change is
Although various measures have been taken to compensate for temperature changes, such as by installing a temperature sensor inside an electronic balance, it is not possible to completely compensate for temperature changes beyond a certain level. Sensitivity calibration must be performed frequently.

Sensitivity calibration of electronic balances is usually performed by loading a weight of known mass onto a load receiver, such as a pan, and updating the sensitivity coefficient so that the measured value in that state matches the mass of the weight. .

In order to facilitate such sensitivity calibration work,
Conventionally, a weight with a known mass was built into an electronic balance, and a so-called weight addition/removal mechanism was installed to load/unload the built-in weight to a load receiver.
It is commonly used to have a function of automatically loading a weight and updating the sensitivity coefficient when a calibration command is issued. This calibration command may be calibrated to be generated automatically when the power is turned on or when the amount of temperature change exceeds a specified value, or may be generated by a switch operation, etc. be.

By the way, an electronic balance is equipped with two measuring sections, a rough measuring section and a fine measuring section, and these two measuring sections share and measure the load acting on the load receiving section, and the total output of both measuring sections is used to measure the load acting on the load receiving section. There is a method to determine the measured value. In other words, the so-called electromagnetic force balance type generates an electromagnetic force to balance the system against the load acting on the load receiver, and measures the load from the coil current required to generate this electromagnetic force. In a balance, for example, a system is provided with two coils, a coarse coil and a fine coil, and the system is approximately balanced by the current flowing through the coarse coil, and in that state, the current is applied to the fine coil by a servo mechanism to accurately balance the system. An example of this is an electronic balance configured to flow .

In such an electronic balance having coarse and fine measuring sections, in addition to the sensitivity calibration described above, it is also necessary to calibrate the ratio of the coarse measuring section to the fine measuring section. In other words, when the output of the coarse measuring section is R, the output of the precise measuring section is P, the fine/coarse ratio is α, and the sensitivity coefficient is K, the measured value W is, for example, W=K(R+αP)...(1) However, even if K is updated so that the measured value W matches the weight mass _W0 when the built-in weight is loaded, the precision measuring part's share P when measuring an unknown mass will be smaller than the precision when calibrating the sensitivity. If α is not equal to or close to the amount shared by the measuring section, the measured value will contain an error. In order to eliminate this error, that is, to always obtain a correct measured value regardless of the size of the amount assigned to the precision measurement section, it is necessary to also calibrate the precision/coarse ratio α.

For this reason, in conventional electronic balances of this type, when a calibration command is issued, the fine/coarse ratio is first calibrated, and then the sensitivity is calibrated.

<Problem to be solved by the invention> As mentioned above, in order to perform high-precision measurements, it is necessary to perform sensitivity calibration frequently, but conventional precision
In electronic balances that have both coarse and coarse measurement sections, the fine and coarse ratios are calibrated each time sensitivity is calibrated, which lengthens the calibration time and reduces work efficiency.

An object of the present invention is to provide an electronic balance that has both fine and coarse measuring sections, which can shorten the calibration time and improve work efficiency.

<Means for Solving the Problems> The configuration for achieving the above object will be explained with reference to the basic conceptual diagram shown in FIG. Part b and precision measurement part c share the measurement, and both measurement parts b and c
The outputs are introduced into the measured value determining means d and summed based on a predetermined fine/coarse ratio α, and the sensitivity coefficient K
is used to determine the measured value W, and at the same time, when a calibration command is issued, the weight adding/removing mechanism e is driven to adjust the load receiving part a.
A built-in weight f is loaded on the body, and a sensitivity calibration means g is introduced to update the sensitivity coefficient K from the measured value W at the time of loading and the known mass of the built-in weight f, and the outputs of the coarse and fine measuring parts b and c are introduced. In a balance equipped with a ratio calibration means h for calibrating the fine/coarse ratio α, a temperature measuring means i for measuring the temperature near the balance.
Then, by introducing the output of the temperature measuring means i, it is determined whether or not the current fine/coarse ratio calibration is necessary based on whether the amount of temperature change from the previous calibration of the fine/coarse ratio α is greater than a preset amount. A determining means j is provided for determining.

Then, when the sensitivity coefficient K is updated due to generation of a calibration command, the calibration of the fine/coarse ratio α is also performed only when the determining means j determines that it is necessary.

<Operation> Calibration of the fine/coarse ratio α is not performed every time a calibration command is issued, but only when the judgment means j determines that it is necessary based on the output of the temperature measurement means i, that is, the calibration of the previous This is executed only when the amount of temperature change from the time of calibration of the fine/coarse ratio α is greater than or equal to a preset amount.

As described above, the fine/coarse ratio α influences the measured value even after sensitivity calibration by the load of the built-in weight f, but the degree of influence is smaller than the sensitivity coefficient K. In other words, in an electronic balance where the measurement range of the fine measurement section c is 1/100 of the measurement range of the coarse measurement section b, assuming that the resolution/measurement range of both measurement sections are the same, the degree of influence on the weighing value will be is 1/100 of K of α. Since the rate of change of K and α based on temperature changes is usually about the same, each time K is updated, α
It is not necessary to calibrate α, and it is sufficient to calibrate α only when the amount of temperature change from the previous calibration of α becomes considerably large. The present invention focuses on this point, determines whether or not it is necessary to calibrate the fine/coarse ratio α based on the amount of temperature change, and calibrates α only when necessary, thereby achieving the intended purpose. ing.

<Embodiment> FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention, and shows an example in which the present invention is applied to an electromagnetic force balance type balance.

The load receiver 1, to which the dish 1a is mounted, is supported by a balance base so as to be freely displaceable in the vertical direction, and is supported by a coarse coil 2a and a fine coil 3a, respectively, which are placed in a static magnetic field by a permanent magnet (not shown). The sum of the respective electromagnetic forces generated by flowing current counteracts the load acting on the load receiver 1 and balances the load receiver 1.

A current is supplied to the coarse coil 2a from the coarse measuring section 2, and a current is supplied from the fine measuring section 3 to the fine coil 3a. Regarding the configuration of the rough measurement section 2 and the fine measurement section 3, various known methods can be adopted, and for example, the following configuration can be adopted.

The coarse measuring section 2 is composed of a constant current source, an electronic switch for chopping its output, and its drive circuit. A current of

The precision measurement section 3 includes a displacement sensor and an amplifier that detect the displacement of the load receiving section 1, a PID controller that inputs the output of the amplifier, and a PID controller that inputs the output of the PID controller and converts it into a current to be passed through the precision coil 3a. A servo mechanism consisting of a power amplifier etc. that converts the current flowing through the fine coil 3a into a voltage value with an output resistor, digitizes it, and supplies it to the control unit 4.
- It is composed of a D converter and the like.

The precision measurement section 3 is configured to be able to select two ranges, large and small, according to commands from the control section 4. When the sample is placed on the plate 1a, the large range is initially selected and the precision measurement section 3 detects the applied load, and the control section 4 determines the duty ratio of the pulse current to be passed through the coarse coil 2a based on the detected data. At the same time as this pulse current is passed through the coarse coil 2a, the precision measuring section 3 is switched to the small range, and the load receiving section 1 is balanced by the sum of the electromagnetic forces generated by the coarse coil 2a and the fine coil 3a. In this state, the control unit 4 determines the measured value by performing calculations based on the above-mentioned equation (1), for example, from the duty ratio of the pulse current flowing through the coarse coil 2a and the current value flowing through the fine coil 3a. do.

The control unit 4 includes a CPU 41, a ROM 42, and a RAM 43.
It is composed of a microcomputer equipped with an input/output port 44, etc. In addition to the normal measurement program, the ROM 42 also has a calibration program written in it, which will be described later.
In addition to the work area, 43 has the sensitivity coefficient K and precision
Areas for storing the rough ratio α and temperature data T ₀ to be described later are set. A display 5 for displaying the determined measurement value is connected to the control section 4.

A built-in weight 6 with a known mass is housed in the balance case, and this built-in weight 6 is connected to a weight addition/removal mechanism 7.
The load receiver 1 can be loaded/unloaded by driving. A drive command for the weight addition/removal mechanism 7 is supplied from the control section 4 .

Inside the balance case, a temperature sensor 8a is disposed near a permanent magnet that creates a static magnetic field, on which a coarse coil 2a and a fine coil 3a are placed, for example, and the output of this temperature sensor 8a is sent to an amplifier, The temperature is taken into the control section 4 via the temperature measuring section 8, which includes a -D converter or the like.

FIG. 3 is a flowchart showing the contents of the calibration program written in the ROM 42, and the operation of each part will be explained below with reference to this diagram.

This calibration program starts with the generation of a calibration command, and in this embodiment, the calibration command is performed by taking temperature data from the temperature measurement unit 8 every moment when the power is turned on and under normal measurement conditions.
It is configured to be generated automatically every time there is a temperature change of 0.5°C, and also configured to be generated by a switch operation etc. if desired by the measurer.

Now, when a calibration command is issued, the current temperature data _T1 from the temperature measuring section 8 is taken (ST1). Next, it is determined whether this calibration command is the first command after the power is turned on (ST2), and if it is the first command, the fine/coarse ratio α is unconditionally calibrated (ST3). ), perform sensitivity calibration (ST5, ST6).

The method for calibrating the fine/coarse ratio α is well known. For example, when the precision measuring section 3 is set to a small range in a balanced state with no load, the duty ratio of the pulse current flowing through the coarse measuring section 2 is set to a predetermined value. Change by the amount equivalent to the mass. As a result, the current flowing through the precision measuring section 3 changes in order to maintain a balanced state, but the correct fine/coarse ratio α can be determined from this amount of change and the above-mentioned amount of change in the duty ratio.

When the fine/coarse ratio α is calibrated, the current temperature data T ₁ is stored as T ₀ in the RAM 43 (ST4).

The method of sensitivity calibration is also known, and a drive command is issued to the weight addition/removal mechanism 7 to load the built-in weight 6 onto the load receiver 1, and its mass is measured. Next, the sensitivity coefficient K is calculated back so that the measured value matches the mass of the known built-in weight.

The fine/coarse ratio α and the sensitivity coefficient K obtained as described above are stored in the RAM 43 and used for determining the measured value in the subsequent measurement routine.

If the calibration command is not the first one after the power is turned on, the temperature T ₀ at the time of the previous calibration of the fine/coarse ratio α
Only when the current temperature T ₁ changes by more than a preset temperature, e.g. 5℃,
Calibrate the fine/coarse ratio α.

That is, the current temperature data T ₁ is compared with the data T ₀ stored in the RAM 43 during the previous calibration of the fine/coarse ratio α (ST7), and if the difference is 5°C or more, proceed to ST3 or below. α and K are updated and T ₁ is stored in the RAM 43 as T ₀ . If the difference is less than 5°C, the process advances to ST5 and only updates K.

As described above, in this embodiment, the sensitivity coefficient K is
It is updated every time there is a temperature change of 0.5℃ or every time the measurer operates a switch.
The fine/rough ratio α is updated only when the temperature changes by 5°C. As described above, the fine/coarse ratio α has a lower influence on measurement errors than the sensitivity coefficient K, and even if the calibration is performed only when the temperature changes by 5° C., no error will be included in the measurement value.

In addition, in the above embodiment, an example was shown in which α and K are updated unconditionally only when the first calibration command is generated after the power is turned on. Until the elapsed time reaches the set time, α and K are updated unconditionally, etc.
Various modifications are possible.

Furthermore, it goes without saying that the temperature difference, which is the criterion for determining whether or not to calibrate the fine/coarse ratio α, should be determined based on the characteristics of the electronic balance to be applied.

Furthermore, it goes without saying that the configurations of the coarse measuring section 2 and the fine measuring section 3 are not limited to the example described above, and any known configuration can be adopted.

<Effects of the Invention> As explained above, according to the present invention, the fine/coarse ratio α is calibrated when a certain temperature change occurs, instead of being performed every time sensitivity calibration is performed as in the past. Because it is executed only when a calibration command is issued, only the necessary calibration operations are performed when a calibration command is issued, and unnecessary operations are not performed. Therefore, the calibration time can be shortened without wasting time. The efficiency of measurement work can be improved.

[Brief explanation of drawings]

Figure 1 is a basic conceptual diagram showing the configuration of the present invention;
The figure is a block diagram showing the configuration of an embodiment of the present invention.
The figure is a flowchart showing the contents of the calibration program written in the ROM 42. DESCRIPTION OF SYMBOLS 1...Load receiving part, 2...Rough measurement part, 3...Precision measurement part, 4...Control part, 6...Built-in weight, 7...Weight addition/removal mechanism, 8...Temperature measurement part.

Claims (1)

[Claims] 1. The load acting on the load receiving part is dividedly measured by a coarse measuring part and a fine measuring part, and the outputs from both measuring parts are introduced into the measurement value determining means and summed based on a predetermined fine/rough ratio. , and determines the measured value using the sensitivity coefficient, and when a calibration command is issued, drives the weight addition/removal mechanism to load the built-in weight on the load receiver, and calculates the measured value at that time and the known value of this built-in weight. In a balance equipped with a sensitivity calibration means for updating the sensitivity coefficient from the mass of The current fine/coarse ratio is determined by introducing a temperature measuring means that measures the temperature and the output of the temperature measuring means and determining whether the temperature change from the previous calibration of the fine/coarse ratio is greater than or equal to a preset amount. It has a determination means for determining whether or not calibration is necessary, and when the sensitivity coefficient is updated due to generation of the calibration command, the calibration of the fine/coarse ratio is also performed only when the determination means determines that it is necessary. An electronic balance that is characterized by being calibrated.