JPH05209775A - Electronic balance - Google Patents

Abstract

PURPOSE:To obtain an electronic balance capable of always performing highly accurate measurement using a part relatively high in temp. dependence without performing too strict adjustment. CONSTITUTION:A temp. detecting means 16 detecting circumferential temp., an A/D conversion part 13 to which the output signal from the temp. detecting means 16 and the output signal from a load detecting part 11 are inputted while changed over and a means judging whether the temp. data converted by the A/D conversion part changes by a definite preset temp. or higher with respect to the temp. data at the time of previous span calibration are provided. A span calibration command is issued at every definite temp. change to automatically renew a conversion coefficient.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to electronic balances.

[0002]

2. Description of the Related Art In a high-precision electronic balance, the ratio between the weighing capacity and the reading limit is 1 / 1.6 million to 1/200 (0.5PP).
M) has also been reached. However, electronic components and other components have relatively large temperature dependence and aging.
For example, among the components, the permanent magnet has a temperature dependence of 200 to
It has 400PPM / ° C and 10PPM / month of aging.

[0003]

Therefore, the temperature dependence of the span is limited to 1 to 2 PPM / ° C. even if various design measures and strict adjustments during manufacturing are performed. Even if the ambient temperature at the time of measurement is changed by 1 ° C., an error corresponding to 2 to 4 counts of the reading limit will occur when the measurement near the weighing is performed. Therefore, such a high-accuracy electronic balance cannot perform reliable measurement unless the room temperature is controlled to a constant temperature, and the error due to secular change must be made unless the span is calibrated almost every day. There is a concern that it may occur, and there is a drawback that it is extremely difficult to use.

The present invention has been made in view of the above, and uses a component having a relatively high temperature dependence and, even without performing strict adjustment, always keeps the balance span constant without any error. An object of the present invention is to provide an electronic balance that can always perform high-precision measurement without performing measurement in a room or the like, or without worrying about an error due to aging.

[0005]

In order to achieve the above object, in the electronic balance of the present invention, an output signal from a load detecting unit for converting a placed load into an electric signal is stored and converted. When the span calibration command is given, the built-in weight of the predetermined mass is placed on the load detection unit, and the output signal from the load detection unit at that time and the above are converted. In an electronic balance capable of updating the conversion coefficient by using a weight mass, a temperature detecting means for detecting an ambient temperature, an output signal from the temperature detecting means and an output signal from the load detecting section are switched and input. And an A / D conversion unit that determines whether the temperature data converted by this A / D conversion unit has changed by a predetermined temperature or more with respect to the temperature data at the time of the previous span calibration. Comprising means, automatically configured may update the conversion factor emit the span calibration command for each of the constant temperature changes.

[0006]

In the functional block diagram shown in FIG. 1, the load detector 1 converts the applied load into an electric signal. The signal is converted into mass in the mass conversion means 2 by the conversion coefficient stored in the conversion coefficient storage means 3 and displayed on the display means 4.
Displayed in. When the span calibration command is issued, the weight adding / removing mechanism 5 puts a built-in weight of a predetermined mass on the load detection unit 1, and the output from the load detection unit 1 at that time is taken into the conversion coefficient calculation means 6. .. The conversion coefficient calculation means 6 newly calculates a conversion coefficient from the output value and the weight mass, and replaces the value with the contents of the conversion coefficient storage means 3 to update the conversion coefficient. The span calibration command is automatically generated from the temperature change determination means 7 as follows. That is,
The temperature change determination means 7 issues a span calibration command when the detected value of the ambient temperature by the temperature detection means 8 has changed by a predetermined temperature or more preset with respect to the temperature data at the previous span calibration.

The detected value from the temperature detecting means and the output from the load detecting section are switched to one A / D converting section and input (see FIG. 2).

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 2, the load detector 11 is a weighing pan 11.
The load on the a is detected by the load sensor 11b, an analog electric signal corresponding to the load is output, and the signal is input to the A / D converter 13 via the switch 12 and converted to a digital signal. , Is input to the control unit 14. The control unit 14 is composed of a microcomputer, and is a CP that executes various calculations and programs and controls each peripheral device.
U14a, a program described later, a memory 14b having an area for storing conversion factors and the like, and an interface circuit 14c for connecting an external peripheral device to the control unit 14 and the like. The digital conversion input from the load detection unit 11 is configured to be converted into mass and displayed on the display unit 15 in the control unit 14 as described later.

The load detector 11 is provided with a temperature sensor 16 close to the load sensor 11b. The temperature sensor 16 detects the temperature in the vicinity of the temperature sensor 16,
It outputs an analog electric signal corresponding to the temperature. The signal is introduced into the A / D converter 13 via the switch 12, converted into a digital signal, and then input to the control unit 14.

The switching unit 12 switches the input signal to the A / D converter 13 to the signal from the load detecting unit 11 or the signal from the temperature sensor 16 based on a command from the control unit 14.

The weight adding / removing mechanism 17 is displaced about a fulcrum 17c 'by an eccentric cam 17b which is rotated by a motor 17a which is driven based on a command from the control section 14, and by the rotation of the eccentric cam 17b. The load sensor 11b can be loaded with the calibration weight 18 or the load can be removed according to a command from the control unit 14.

FIG. 3 is a flow chart showing a data processing program written in the memory 14b according to an embodiment of the present invention.

First, a command is issued to the switching device 12 to make an input signal to the A / D converter 13 a signal from the temperature sensor 16, and the digital conversion temperature data t is fetched (ST.
1, ST2). When the temperature data t does not have a difference equal to or more than a preset temperature T (for example, 0.5 ° C.) with respect to the temperature data t o at the time of the previous span calibration described later, the switching device 12 causes the A / D converter 13 An input signal to the load detector 11 is used as a signal from the load detector 11, and its digital conversion data w is fetched (ST3, ST4, ST5). Then, the data w is converted into mass W using the conversion coefficient K currently stored in the memory 14b as follows: W = K · w (1) Tare subtraction, zero point correction, etc. Calculation processing is performed to determine the weighing display value and display it on the display 15 (ST6, ST
7, ST8). Usually, such a measurement routine is executed.

If the temperature in the vicinity of the load sensor 11b changes by more than the above temperature due to a change in room temperature or the like, the data t from the temperature sensor 16 is read at a constant cycle, in this example, every time the measured value is displayed. Therefore, the span calibration routine from ST3 onward is executed immediately after ST3.
In this routine, the detected temperature data t is stored as to and used as a reference temperature for the next span calibration ("the temperature data to be the time of the previous span calibration is to be used at the time of the next span calibration", and the switch 12 Then, the output of the load sensor 11b is input to the A / D converter 13 and its digital conversion data w is sampled (ST10, ST11).
If the value is not within the range of the specified value near zero load, it is determined that the sample is placed on the weighing pan 11a, that is, the measurement is in progress, and if an alarm is issued and calibration is not performed, a reliable measured value can be obtained. Notifying that it is not possible and urging the sample to be removed from the weighing pan 11a (ST12, ST13). If it is within the above range, the data w is stored as wo (ST1
4), the motor 17a of the weight adding / removing mechanism 17 is driven to rotate the eccentric cam 17b by a predetermined angle, and the lever 17c is displaced downward to load the calibration weight 18 on the load sensor 11b (ST15). After waiting for a predetermined specified time based on the response characteristic of 1) and the stability of the data w, the data w is fetched (ST16, ST17). Then, the conversion coefficient K (or S) is calculated by the data w by the load of the calibration weight 18, the above-mentioned data wo at the time of no load, and the mass P of the calibration weight 18, K = P / (w-wo) ... ... (2) (or S = (w-wo) / P ... (2) '), and the value is replaced with the value stored so far to update the conversion coefficient K (ST18). ).

Then, the motor 17a is driven to remove the load of the calibration weight 18 on the load sensor 11b by the weight adding / removing mechanism 17 (ST19), and the routine proceeds to ST5 to return to the normal measurement routine.

When S shown in (2) 'is used as the conversion coefficient, the conversion formula (1) in ST6 is changed to the following (1)'.

W = w / S (1) 'In addition, regarding the sampling of the data w o when there is no load during span calibration and the data w when the calibration weight 18 is loaded, digital conversion data from the load sensor 11 b is specially used. It is desirable that a large number of are averaged to obtain an accurate conversion factor. Since the temperature change is gradual, it is not always necessary to check the temperature t every time the display is performed once. For example, as shown in FIG. 5, ST20 is followed by ST20 and ST2.
1 may be provided and t may be checked every Q times of display.

Next, as another embodiment of the present invention, an example will be described in which, in addition to the calibration for each fixed temperature change, the calibration for each fixed time elapse can be performed. In this case, ST3 'shown in FIG. 4 may be inserted between ST3 and ST4 in the flow chart of the above-mentioned embodiment. As a result, the calibration routine will be executed when the temperature has changed more than a predetermined temperature with respect to the temperature at the previous span calibration, or when a predetermined time has passed since the last span calibration, whichever comes first. To be done. Even if the calibration by time is executed, the process proceeds from ST3 'to ST9, and the temperature at that time is stored as to, so there is no waste that the calibration by the temperature change is performed immediately after the calibration by time. ..

The elapsed time measuring means does not need to be separately equipped with hardware such as a clock function, and can be easily known by the number of turns of the program. For example,
Between ST7 and ST8, a step of counting up the contents of the register each time the routine is passed, and a step of resetting the contents when the calibration routine is executed may be provided, for example, in the next stage of ST19. Further, it is more complete if the calibration routine is executed once unconditionally when the power is turned on, and then the calibration is performed by the temperature change and the lapse of time.

[0021]

Since the present invention is configured as described above, the span calibration is automatically executed at every predetermined temperature change and the measured value is always kept within a certain error. Can obtain highly reliable measured values and eliminates the need to prepare a special room such as a temperature-controlled room for measurement. In addition, the temperature dependence of the span of the balance
Since it can be roughened about 3 to 10 times as compared with the case where the present invention is not adopted, the cost of the component can be reduced and the cost can be reduced by simplifying the adjustment work.

Further, if it is constructed so that it is automatically calibrated every time a certain period of time elapses, it is more effective because there is no concern about aging.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing a configuration of the present invention.

FIG. 2 is a configuration diagram of an embodiment of the present invention.

FIG. 3 is a flowchart showing a data processing program according to an embodiment of the present invention.

FIG. 4 is a flowchart showing a main part of a data processing program according to another embodiment of the present invention.

FIG. 5 is a flowchart showing a main part of a data processing program according to another embodiment of the present invention.

[Explanation of symbols]

11 load detection unit 11a weighing pan 11b load sensor 12 switcher 13 A / D converter 14 control unit 14a CPU 14b memory 14c interface circuit 15 indicator 16 temperature sensor 17 weight adjustment mechanism 17a motor 17c lever 18 calibration weight

Claims (1)

[Claims] 1. An output signal from a load detection unit for converting a placed load into an electric signal is converted into a mass by a stored conversion factor and displayed, and when a span calibration command is given, Place the built-in weight of the predetermined mass on the load detection unit, and use the output signal from the load detection unit and the mass of the weight at that time to update the conversion factor of the electronic balance. A temperature detecting means for detecting, an output signal from the temperature detecting means and an output signal from the load detecting section are switched and inputted.
The A / D conversion unit and means for determining whether the temperature data converted by the A / D conversion unit has changed by a predetermined temperature or more with respect to the temperature data at the time of the previous span calibration, An electronic balance characterized in that it is configured such that the span calibration command is issued for each change and the conversion coefficient is automatically updated.