JPH06167383A - Electronic balance - Google Patents

Abstract

PURPOSE:To prevent display of weighed value from stopping due to detection of corrective information in an electronic balance in which an operational processing means is connected through at least an amplifier and an ADC with a load cell and output voltage of the ADC is corrected, at the time of weighing, according to corrective information, i.e., output voltage from the ADC under a state where the input terminals of the amplifier separated from the load cell by a switching means are short-circuited. CONSTITUTION:The electronic balance comprises timing control means 23, 25, 26 for detecting the output voltage from an ADC 11 sporadically in a short time, means 25 for temporarily storing output voltages detected sequentially at a drive timing as measurements, and means 23 for generating corrective information from a predetermined number of temporarily stored measurements. Detection of corrective information, which may cause stoppage of display of weighed value of an article, is carried out sporadically in a short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic scale using a load cell.

[0002]

2. Description of the Related Art Generally, an electronic scale has a load cell formed by attaching four strain gauges bridge-connected to a strain-generating body having one end fixed to a main body base and the other end having a saucer. , A, which is an amplifier, a low-pass filter, and an analog-digital converter at the output terminal of this load cell
It has a structure in which a CPU (Central Processing Unit) which is an arithmetic processing unit is sequentially connected via a DC (Analog-Digital Convertor).

In such an electronic scale as described above, since the output voltage of the load cell changes according to the weight of the articles loaded on the tray, this is amplified by an amplifier and noise is removed by a low pass filter. A / D with ADC
(Analog / Digital) conversion is performed and the CPU or the like detects it as weight information. By doing so, the electronic scale can electrically measure the weight of the article and output it as a digital number or the like to a display, a printer, or the like.
However, in an electronic scale that uses a load cell like this,
The output value of the amplifier or ADC may fluctuate due to a temperature change and the like, and the measured value may change, which lowers the reliability of the electronic scale.

Therefore, an electronic balance that solves such a problem is disclosed in Japanese Patent Application Laid-Open No. 4-213026 filed by the present applicant. Therefore, the electronic scale disclosed in the above publication is
Here, one conventional example will be described in detail below with reference to FIGS. First, in the electronic scale 1, as illustrated in FIG. 3, a short circuit line 6 for connecting the two input terminals 4 and 5 of the amplifier 3 connected to the load cell 2 is formed. Analog switches 7 and 8 as switching means are provided on one of the input terminals 4. The output terminal of the amplifier 3 is connected to the A line via the correction line 9 and the weighing line 10 which are formed in parallel.
A CPU 12 connected to the DC 11 and connected to the ADC 11 has a keyboard 14 for inputting various information, and a ROM (Read
Only Memory) (not shown), RAM (Random Access Memory) (not shown) that temporarily stores various types of information in a freely updateable manner,
A reference clock (not shown) or the like that outputs a predetermined clock pulse is connected.

In the electronic scale 1, an analog switch 15 is formed on the correction line 9 and
An analog switch 16, a capacitor 17, a low-pass filter 18 and an analog switch 19 are sequentially formed on the measuring line 10, and these analog switches 7, 8, 15, 16 and 19 form a line switching means. There is. Then, the analog switches 7, 8 and 1 forming the line switching means and the switching means.
A voltage measuring unit, a voltage correcting unit, and the like are formed by the CPU 12 and the like in which 5, 16, and 19 are connected to the control terminals 20 and 21.

In the electronic balance 1 having such a structure, the analog switches 8, 16 and 19 are turned on and the analog switches 7 and 15 are turned off while the switching means and the line switching means are at rest, and the switching means is turned off. And the analog switch 8, 1 while the line switching means is operating.
6, 19 are turned off and analog switches 7, 15
Turns on. Then, as illustrated in FIG. 4, for the operation and suspension of the switching means and the line switching means as described above, for example, the CPU 12 controls the control terminal 2 by counting the clock pulse of the reference clock every predetermined number.
The switching is performed according to the control signals output from 0 and 21.

Therefore, in the electronic scale 1, the switching means and the line switching means are stopped by the timing control as described above so that the amplifier 3 is connected to the load cell 2 and is connected to the ADC 11 via the measuring line 10. In this state, an item (not shown) is weighed. That is, the output voltage of the load cell 2 that changes according to the weight of the article is amplified by the amplifier 3, noise is removed by the low pass filter 18, A / D converted by the ADC 11, and the CPU 12 is activated.
The weight of the article is displayed and output as a digital number or the like on the display 13 by being detected as the weight information by.

In the electronic scale 1, the amplifier 3 having the input terminals 4 and 5 short-circuited by the switching means and the line switching means operated by the timing control as described above is connected to the ADC 11 via the correction line 9. Then the CPU
The output voltage of the amplifier 3 or ADC 11 is measured by 12. That is, in this state, the residual voltage of the amplifier 3 or the ADC 11 is detected as the output voltage in the CPU 12 regardless of the output voltage of the load cell 2, and this voltage value is R as the measurement result of the output voltage of the amplifier 3 or the ADC 11.
It is temporarily stored in AM or the like.

Then, when the switching means and the line switching means are stopped again and the weighing of the articles is restarted, the CPU 1
By the control of 2, the measured value of the article is corrected according to the variation value of the output characteristic of the amplifier 3 or the ADC 11.

By doing so, the electronic scale 1 is
Since the output characteristics of the amplifier 3 and the ADC 11 are periodically measured and the measured value of the article is corrected, accurate measurement can always be performed even if the output characteristics of the amplifier 3 and the ADC 11 change due to temperature change or charging. it can.

In the electronic scale 1, as shown in FIG. 4, the timing control is performed so that the operating time and the rest time of the switching means and the line switching means are the same, but the present invention is not limited to this. The method is not limited to the above method, and as illustrated in FIG. 5, timing control may be performed so that the operating time of the switching means and the line switching means is longer than the rest time. That is, in this electronic scale 1, when the output characteristics of the amplifier 3 and the ADC 11 are measured, the amplifier 3 and the ADC 11 are directly connected by the correction line 9 so that the low-pass filter 18, which requires a long time for energization, is not provided. 3 and the output characteristics of the ADC 11 can be completed in a short time and the time for actually weighing the article can be lengthened, and by doing so, it is possible to contribute to the improvement of the reliability of the device.

[0012]

In the electronic balance 1 described above, the output characteristics of the amplifier 3 and the ADC 11 are periodically measured to correct the measured value of the article, so that the amplifier 3 and the ADC 11 are subject to temperature change and charging. Accurate weighing can be performed even if the output characteristics of the device fluctuate.

Here, in the electronic balance 1 described above, the amplifier 3 and the ADC 1 are operated at the timings illustrated in FIGS. 4 and 5.
Although the measurement of the output voltage of 1 has been illustrated, the output voltage sampled in this way is extremely unreliable, so in practice, sampling is performed multiple times during one measurement timing. Then S / N (Signal / No
ise) is improved.

However, such an amplifier 3 and ADC 11
Since the output voltage of the load cell 2 cannot be output as the weight information on the display 13 during the measurement of the output voltage of 1, the number of samplings of the output voltage of the amplifier 3 and the ADC 11 is increased as described above, and the measurement timing of one time is measured. Is extended, the display content of the display 13 is stopped for a long time.

More specifically, the time required for one sampling of the output voltage of the amplifier 3 and the ADC 11 is 0.2 (sec).
Then, if sampling is performed eight times within one measurement timing, the display content of the display 13 is stopped for 1.6 (sec) during this measurement. For example, immediately after an article (not shown) is placed on the saucer (not shown) of the electronic scale 1, the output voltage of the load cell 2 is not stable due to its vibration and the like, so that the display content of the display 13 continues. However, the amplifier 3
When the output voltage of the ADC 11 or the measurement of the output voltage of the ADC 11 is started and the display content of the display 13 is stopped for 1.6 (sec), the customer may feel distrust, which is not preferable.

[0016]

An arithmetic processing means is connected to a load cell through at least an amplifier and an analog-digital converter in order, and at least one of two input terminals of the amplifier is separated from the load cell and short-circuited to each other. Switching means is provided, voltage measuring means for measuring the output voltage of the analog-digital converter is provided during the operation of the switching means, and timing control means for driving the switching means sporadically for a short time is provided. The information storage means for temporarily storing the measurement results sequentially output by the voltage measurement means at the driving timing is provided, and the information generation means for generating the correction information from the predetermined number of measurement results temporarily stored by the information storage means is provided. The switching operation is performed according to the correction information generated by the information generating means. It provided a voltage correction means for correcting the output voltage of the analog-to-digital converter connected to the amplifier by pauses.

[0017]

The switching means for separating the two input terminals of the amplifier from the load cell to short-circuit them is sporadically driven for a short time by the timing control means, and the measurement result sequentially output by the voltage measuring means at this drive timing is stored as information. The information generation means generates correction information from the temporarily stored predetermined number of measurement results, and the output voltage of the analog-digital converter connected to the amplifier is voltage-corrected according to the correction information when the switching means is inactive. Means compensate.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. In this embodiment, the same parts as those of the electronic balance 1 described above as a conventional example are designated by the same names and reference numerals, and detailed description thereof will be omitted. First, in this electronic scale 22, one end is fixed to a main body base (not shown) and the other end is provided with a saucer (not shown). A load cell 2 is formed by attaching a strain gauge (not shown), and the amplifier 3 is connected to the output terminal of the load cell 2. Therefore, in this electronic balance 22, as illustrated in FIG. 1, an analog switch 7 which is a switching means for short-circuiting the two input terminals 4 and 5 of the amplifier 3 in a freely connectable / separable manner, the amplifier 3 and the load cell 2 are provided.
An analog switch 8 which is a switching means for connecting and disconnecting and is separately provided here together with a dedicated line. The output terminal of the amplifier 3 is connected to the ADC 11 via the correction line 9 and the measurement line 10 which are formed in parallel, and the display 23 is connected to the CPU 23 which is the arithmetic processing means connected to the ADC 11. The keyboard 14, the ROM 24, the RAM 25, the reference clock 26, etc. are connected.

Here, in the electronic balance 22 of this embodiment, an analog switch 27, a low-pass filter 28, an analog switch 29, etc. are sequentially formed on the correction line 9, and on the measurement line 10, Analog switch 1
6, a capacitor 17, a low pass filter 18, an analog switch 19 and the like are sequentially formed. Therefore, in this electronic scale 22, the analog switches 7, 8, 16, 1 are used.
A line switching means is formed by 9, 27, 29, and the analog switches 7, 8, 16, 19, 2 forming such a line switching means or switching means.
Control terminals 20 and 21 of the CPU 23 are connected to the CPUs 7 and 29.

In the electronic scale 22, the voltage measuring means for measuring the output voltage of the ADC 11 and the amplifier in which the input terminals 4 and 5 are short-circuited is formed by the CPU 23 or the like. Switch 7,
The timing control means for driving 8, 16, 19, 27, and 29 sporadically for a short time includes the CPU 23 and the RA.
It is formed of M25, the reference clock 26, and the like. Further, in the electronic scale 22, timing setting means for variably setting the drive timing of the timing control means by updating the storage information in the RAM 25 is formed by the CPU 23, the keyboard 14 and the like. Information storage means for temporarily storing the measurement results sequentially output by the voltage measurement means at such drive timing of the timing control means is formed by the RAM 25. Further, in the electronic scale 22, the information generating means for appropriately generating the correction information from the predetermined number of measurement results temporarily stored in the RAM 25 and the ADC 11 at the time of weighing according to the correction information generated by the information generating means. A voltage correction means for correcting the output voltage is formed by the CPU 23 and the like.

In such a structure, the electronic scale 22
The processing operation when weighing the article and the processing operation when correcting the weighing characteristic will be described in detail below with reference to the flowchart of FIG. First, in the electronic scale 22, the CPU 23 executes initialization when the main body power source (not shown) is turned on, and then the display 1 is operated as a preparatory operation.
3 light emitting elements (not shown) are sequentially driven. At this time, in the electronic scale 22, it takes time for the characteristics of the load cell 2 immediately after starting to stabilize. Therefore, in order to secure this time, the display 13 performs a preparatory operation for more than ten seconds. In addition to rejecting the measurement operation of No. 1, the correction of the measurement characteristic as described below is started.

First, in the electronic scale 22, for example, by counting clock pulses output from the reference clock 26 up to the number of clocks set in the RAM 25, C
The PU 23 functions as a timer, and such a timer starts counting after completion of initialization.

Therefore, until the timer counts up, the switching means and the line switching means are suspended as the timing for weighing the articles, the analog switches 8, 16 and 19 are turned on, and the analog switches 7 and 27 are turned on. , 29 are turned off. Then, with the amplifier 3 connected to the load cell 2 connected to the ADC 11 via the weighing line 10 in this manner, weighing of articles is performed as in the conventional electronic scale 1. That is,
The output voltage of the load cell 2, which changes according to the weight of the article, is amplified by the amplifier 3, noise is removed by the low-pass filter 18, A / D converted by the ADC 11, and then CP.
The weight information is detected by U23. Therefore, the CPU 23 uses the weight information detected as described above as R
The flicker process is executed together with the plurality of weight information stored in the RAM 25 and stored in the RAM 25 in advance.

Here, the flicker process is a process for generating one piece of information from a plurality of pieces of information in order to improve S / N, and here, as described above, one piece of weight information is stored in the RAM 25. It is executed every time. More specifically, the latest eight pieces of weight information in the RAM 25 are compared with each other, and if there are five or more pieces of the same weight information, this is output as regular weight information. If, as a result of the comparison as described above, there are five or less pieces of the same weight information, the number of pieces of weight information that is the same as the latest three pieces of weight information in the RAM 25 is calculated, and the largest piece of weight information is set as the regular weight information. Output.
In addition, in the electronic scale 22, if one piece of weight information cannot be extracted even by the above-described processing, or if eight pieces of weight information do not exist in the RAM 25, the weight information to be subjected to the flicker processing is more unstable than the allowable range. It returns to the count state of the timer.

Therefore, the CPU 23 which has completed the flicker processing as described above confirms the presence or absence of the correction information in the RAM 25, and corrects the weight information with the correction information if the correction information exists. Then, the rounding process is executed on the weight information thus corrected, and a digital number or the like is displayed and output on the display 13 corresponding to the weight information for which the rounding process is completed.

The electronic scale 22 is designed to measure the articles as described above until the timer in the CPU 23 counts up.
When the timer in 3 counts up, this timer is reset and started, and then the correction of the output characteristic is started. Therefore, in this electronic scale 22, C
The analog switches 8, 16, 19 are controlled by the PU 23.
Is turned off and the analog switches 7, 27 and 29 are turned on, and thus the amplifier 3 having the input terminal short-circuited and separated from the load cell 2 is connected to the ADC 11 via the correction line 9. .

In such a state, the CPU 23
Irrespective of the output voltage of the load cell 2
Since the residual voltage of DC11 is detected as the output voltage,
The output voltage is subjected to A / D conversion by the ADC 11 after noise is removed by the low pass filter 28, and detected by the CPU 23 as a measurement result. Therefore, this CPU 23
The measurement result detected as described above is stored in the RAM 25 as temporary correction information, and the flicker process is executed together with the plurality of temporary correction information stored in advance in the RAM 25.

That is, the eight latest provisional correction information in the RAM 25 are compared with each other, and if the same correction information is five or more, this is output as the normal correction information. And
If, as a result of the comparison as described above, there are five or less identical pieces of correction information, the number of pieces of weight information that is the same as the latest three pieces of weight information in the RAM 25 is calculated, and the largest amount of weight information is output as regular weight information. . In this electronic scale 22, when one piece of correction information cannot be extracted even by the above-described processing, or when eight pieces of correction information do not exist in the RAM 25, the correction information for flicker processing is more unstable than the allowable range. It returns to the count state of the timer.

Therefore, the CP which has completed the flicker processing
The U23 uses the correction information detected by the flicker processing as the normal correction information for actually correcting the weight information in the RAM 25.
Stored in another area of the above, and when this is completed, it returns to the counting state of the timer.

By doing so, the electronic balance 22 periodically measures the output characteristics of the amplifier 3 and the ADC 11 and corrects the measured value of the article, so that the amplifier 3 and the ADC 11 are changed due to temperature change or charging. Even if the output characteristic of fluctuates, accurate measurement can always be performed. Moreover, in the electronic scale 22, sampling and display of weight information is repeated until the timer in the CPU 23 counts up, and when the timer counts up, the timer is reset and started, and then the correction information is sampled. Is executed only once, the sampling of the weight information is continuously executed for a long time, and the sampling of the correction information is sporadically executed for an extremely short time.

In other words, in this electronic scale 22, the sampling of the weight information cannot be executed during the sampling of the correction information. Therefore, if the correction information is sampled during the weighing of the article, the display content of the display 13 is stopped.
Since this is sporadically carried out in an extremely short time, there is no visual distrust of the customer. Moreover, in the electronic scale 22, even if only one correction information is sampled within one measurement timing as described above, the correction information to be sampled sporadically is accumulated in the RAM 25 and the flicker processing is performed for each predetermined number. Therefore, it is possible to reduce the S / N and ensure good reliability.

For example, in the electronic scale 22, if the time required for one sampling of the output voltage of the amplifier 3 and the ADC 11 is 0.2 (sec) and the count time of the timer in the CPU 23 is 2.0 (sec), the display 13 is displayed. The display content of is only stopped for 0.2 (sec) every 2.0 (mm), and this does not give discomfort to personnel visually.

In the electronic scale 22, for example, the execution time and execution interval of sporadic sampling can be changed by changing the count time of the timer by updating the information stored in the RAM 25 by operating the keyboard 14. Since it can be set freely, it is possible to deal with product errors such as the load cell 2 and the amplifier 3. In addition to fixedly setting the sporadic sampling execution time and execution interval in this way, for example, switching the sampling execution interval to a short time immediately after startup and switching to a long time after a lapse of a predetermined time. Can also be implemented. By doing so, the characteristics of the load cell 2 are unstable for about 30 minutes immediately after starting, but it is possible to contribute to the high performance of the electronic balance 22 by precisely repeating the correction until the characteristics become stable. .

[0034]

As described above, the present invention is provided with the timing control means for driving the switching means sporadically for a short time, and temporarily stores the measurement results sequentially output by the voltage measuring means at the drive timing of the timing control means. Information storage means is provided, and information generation means for generating correction information from a predetermined number of measurement results temporarily stored in this information storage means is provided. In accordance with the correction information generated by this information generation means, the switching means is suspended and connected to the amplifier. By providing the voltage correction means for correcting the output voltage of the analog-to-digital converter, the detection of the correction information that causes the stop of the display of the weighing value of the article is sporadically performed in a short time, so that the personnel feel distrust. It is possible to prevent the occurrence of the above.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit structure of an electronic scale according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a detection timing of weight information and correction information.

FIG. 3 is a block diagram showing a circuit structure of a conventional electronic balance.

FIG. 4 is a time chart showing a specific example of the operation timing of an analog switch that is a switching means or the like.

FIG. 5 is a time chart showing a modified example of the operation timing of an analog switch that is a switching means or the like.

[Explanation of symbols]

2 load cell 3 amplifier 4,5 input terminal 7,8 switching means 11 analog-digital converter 22 electronic balance 23 arithmetic processing means and voltage measuring means and information generating means and voltage correcting means 23, 25, 26 timing control means 25 information storing means

Claims (1)

[Claims] 1. A load cell, an amplifier that amplifies an output voltage of the load cell, an analog-digital converter that converts the output voltage of the amplifier into a digital value, and weight information is generated from a digital value output by the analog-digital converter. Arithmetic processing means, switching means for separating at least one of the two input terminals of the amplifier from the load cell to short-circuit each other, and voltage measuring means for measuring the output voltage of the analog-digital converter during the operation of the switching means. A timing control means for driving the switching means sporadically for a short time, an information storage means for temporarily storing the measurement result sequentially output by the voltage measurement means at the drive timing of the timing control means, and the information storage means. Corrected from a predetermined number of measurement results temporarily stored by It is characterized by comprising information generating means for generating information and voltage correcting means for correcting the output voltage of the analog-digital converter connected to the amplifier when the switching means is stopped according to the correction information generated by the information generating means. And an electronic scale.