JPH04323521A - Load cell scale - Google Patents

Abstract

PURPOSE:To improve measurement accuracy and to increase speed of the measurement at the same time by using a load cell scale, for which a calculation circuit is connected to a load cell to which a commercial power source is connected, through amplifier, low pass filter and A/D converter and so on. CONSTITUTION:A band pass filter 6, the cut-off frequency of which is the frequency of a commercial power source 2, is provided between an amplifier 5 and an A/D converter 8. By cutting off a peak noise generated by the effect of the commercial power source 2 by the band pass filter 6, the measurement accuracy is improved while the measurement speed is increased, without using a low pass filter which is of high accuracy but is of slow response.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load cell scale in which an arithmetic circuit is connected to a load cell connected to a commercial power source.

0002

2. Description of the Related Art A conventional load cell scale includes a load cell that supports a tray on which various articles are loaded, and a commercial power source connected to an input terminal via a power circuit.
A CPU (Central Processing) is connected to the output terminal of this load cell through an amplifier, a low-pass filter, and an A/D (Analog/Digital) converter.
It has a structure in which arithmetic circuits such as ing unit) are connected. In such a load cell scale, when an article is loaded onto the tray, the load cell, which is driven by the power of the commercial power supply, outputs an analog signal according to the weight of the article.This analog signal is amplified by an amplifier and then passed through a low-pass filter. to reduce noise components caused by vibrations on the floor, etc.
The weight of the article is calculated by converting the signal into a digital signal using a /D converter and processing the signal using an arithmetic circuit.

0003

SUMMARY OF THE INVENTION Since the load cell scale described above can electrically calculate the weight of an article, it is used in electronic toll scales and the like. In this type of load cell scale, the noise component included in the analog signal output from the load cell has a peak of about 50 (Hz) due to the influence of the oscillation frequency of the commercial power supply, so this noise component is removed by a low-pass filter. I try to reduce it with a filter. Nowadays, there is a demand for improving the weighing accuracy of load cell scales, and as a means to meet this demand, as exemplified as ■ in Fig. 3,
Consideration has been given to using a high-precision low-pass filter to increase the amount of attenuation. By doing this, approximately 50 (
Since the peak noise (Hz) can also be reduced favorably, extremely highly accurate measurement can be achieved.

However, since a high-precision low-pass filter has a characteristically low response, the time required to determine a weighed value becomes long, and the weighing speed of the load cell scale decreases. In order to solve this problem, it is possible to use a low-precision low-pass filter as shown in Figure 3 (■), but this will reduce noise components at high frequencies such as 50 (Hz). It is impossible.

[0005]

[Means for solving the problem] A load cell is provided whose input terminal is connected to a commercial power source via a power supply circuit, and an amplifier, a low-pass filter, and an A/D are connected to the output terminal of the load cell.
An arithmetic circuit is connected sequentially through a converter, and an analog signal output from a load cell driven by commercial power supply according to the weight of the article is amplified by an amplifier, noise components are reduced by a low-pass filter, and then A/D is applied. In a load cell scale that uses a converter to convert the signal into a digital signal and uses an arithmetic circuit to calculate the weight of the article, a bandpass filter whose cutoff frequency is the oscillation frequency of the commercial power source is installed between the amplifier and the A/D converter. Established.

[0006]

[Operation] By installing a bandpass filter whose cutoff frequency is the oscillation frequency of the commercial power supply between the amplifier and the A/D converter, the peak noise generated in the analog signal due to the influence of the commercial power supply is removed by the bandpass filter. Since it is possible to cut it off with , it is possible to improve the weighing accuracy without using a low-pass filter with high precision but low response.In this way, it is possible to improve the response of the low-pass filter without reducing the weighing accuracy. As a result, it is possible to increase the metering speed.

[0007]

[Embodiment] An embodiment of the present invention will be explained based on the drawings. First, in this load cell scale 1, a commercial power supply 2 is connected to an input terminal of a load cell 4 via a power supply circuit 3.
A CPU 9, which is an arithmetic circuit, is connected to the output terminal of the load cell 4 via an amplifier 5, a bandpass filter 6, a low-pass filter 7, and an A/D converter 8 in this order. In addition, this CPU 9 has a display 10 and a keyboard 1.
1 is connected to the load cell 4, and a saucer (not shown) is mechanically connected to the load cell 4. Further, in this load cell scale 1, the cutoff frequency of the bandpass filter 6 is 50 (Hz), which is the oscillation frequency of the commercial power source 2.

With this configuration, in this load cell scale 1, the operation mode of the CPU 9 is set by operation input from the keyboard 11, and then the receiving tray (
(not shown), the load cell 4 driven by the power of the commercial power source 2 outputs an analog signal according to the weight of the article. Therefore, this analog signal is sent to the amplifier 5.
The signal is amplified by a bandpass filter 6 and a lowpass filter 7 to reduce noise components, and is converted into a digital signal by an A/D converter 8 and subjected to arithmetic processing by a CPU 9. Therefore, the weight of the article is calculated by this calculation process, and this numerical value is displayed on the display 10.

[0009] In this load cell scale 1, as illustrated by ■ in Fig. 2, the low-pass filter 7 has high responsiveness, so the time required to determine the weighing value is shortened and the weighing speed is improved. . Since noise components at a high frequency of 50 (Hz), which cannot be effectively reduced by such a low-pass filter 7, are blocked by the band-pass filter 6, the load cell scale 1 has extremely good weighing accuracy. In other words, this load cell scale 1 has a commercial power supply 2
By blocking the 50 (Hz) noise component that occurs in analog signals due to the influence of The low-pass filter 7 with good response realizes high-speed metering.

Note that in this embodiment, the bandpass filter 6
Although the load cell scale 1 is shown as an example in which the load cell scale 1 is provided between the amplifier 5 and the low-pass filter 7, the present invention is not limited to the above structure. For example, it is also possible to provide it between the low-pass filter 7 and the A/D converter 8. In addition, in this embodiment, the commercial power supply 2
Although the explanation has been made assuming the Kanto region of Japan where the oscillation frequency of It is set corresponding to the oscillation frequency of.

[0011]

[Effects of the Invention] As described above, the present invention provides a load cell whose input terminal is connected to a commercial power supply via a power supply circuit.
An arithmetic circuit is connected to the output terminal of this load cell through an amplifier, a low-pass filter, and an A/D converter in order, and the amplifier amplifies the analog signal that the load cell, which is driven by the power of the commercial power supply, outputs according to the weight of the article. In a load cell scale that uses a low-pass filter to reduce noise components, converts the signal into a digital signal using an A/D converter, and uses an arithmetic circuit to calculate the weight of the item, a band with the oscillation frequency of the commercial power source as the cutoff frequency is used. Pass filter with amplifier and A/
By installing it between the D converter and the bandpass filter, the peak noise generated in the analog signal due to the influence of the commercial power supply can be blocked by a bandpass filter, so a lowpass filter with high precision but low response can be used. In this way, it is possible to use a low-pass filter with good response without reducing weighing accuracy, which makes it possible to achieve faster weighing speeds and improve weighing accuracy. This has effects such as being able to obtain a load cell scale that is compatible with high weighing speed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram of a band-pass filter and a low-pass filter.

FIG. 3 is a characteristic diagram of a low-pass filter showing a conventional example.

[Explanation of symbols]

1 Load cell scale 2
Commercial power supply 3 Power supply circuit 4 Load cell 5
Amplifier 6 Bandpass filter 7
Low pass filter 8
A/D converter 9
Arithmetic circuit

Claims (1)

[Claims] 1. A load cell is provided whose input terminal is connected to a commercial power source through a power supply circuit, and an arithmetic circuit is connected to the output terminal of the load cell through an amplifier, a low-pass filter, and an A/D converter in sequence, The load cell driven by the power of the commercial power supply outputs an analog signal according to the weight of the article, which is amplified by the amplifier, noise components are reduced by the low-pass filter, and then converted into a digital signal by the A/D converter. In the load cell scale, the weight of the article is calculated by the arithmetic circuit, and a bandpass filter whose cutoff frequency is the oscillation frequency of the commercial power source is provided between the amplifier and the A/D converter. A load cell scale characterized by: