JPH03172720A - Load cell scale - Google Patents

Abstract

PURPOSE:To attain a high-accuracy measurement by providing a computing element which increases the resolution of A/D converters by N<1/2> times or above when the number of the A/D converters is N and divides the sum of their digital outputs by the multiple. CONSTITUTION:The outputs of respective load cells 2a - 2d are amplified by operational amplifiers 11a - 11d and A/D-converted 12a - 12d. The results are added 14, the sum is divided by the resolution through a divider 15, and the load value is stored 16. Further, the cells 2a - 2d which are A/D-converted 12a - 12d are put in relation between the load and digital outputs based upon the load. Further, the quantization error of the A/D converters is constant regardless of whether the resolution is large or small, so when the number of the A/D converters in use is N, the error of the load generated by the addition becomes N<1/2> times by a variance adding method, so the digital outputs are added while the resolution of the individual A/D converters is set >=N<1/2> times as large as necessary irreducible resolution. The value after the addition is equalized to the sum of values divided by the multiple of the resolution and the quantization error can be improved to the value where one A/D converter is used.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a load cell scale that measures weight by converting the outputs of M number of load cells using a plurality of analog-to-digital converters. .

(Prior Art) A conventional load cell scale of this type connects an analog-to-digital converter to each of a plurality of load cells, and measures the weight by adding up the outputs of these analog-to-digital converters.

(Problem to be solved by the invention) However, if the outputs from each load cell are converted by each analog-to-digital converter and then added together, the quantization error of the analog-to-digital converter also increases. Since they are added, there is a problem in that when there are N analog-to-digital converters, the accuracy after addition decreases to 1/rT.

The present invention was made in view of the above problems, and an object of the present invention is to provide a load cell scale that can perform highly accurate measurements even when using a plurality of analog-to-digital converters.

[Structure of the invention]

(Means for Solving the Problems) The present invention converts the outputs of a plurality of load cells using a plurality of analog-to-digital converters, and adds the digital outputs of these analog-to-digital converters by an adding means to calculate the weight. In a load cell scale for measuring, when the number of analog-to-digital converters is N, the resolution of the analog-to-digital converter is set to be Fx times or more, and a dividing means is provided for dividing the added digital output by this multiple. It is equipped with.

(Function) The present invention converts the outputs of a plurality of load cells with a plurality of analog-to-digital converters, adds the digital outputs of these analog-to-digital converters with an adding means, and divides them with a dividing means. Measure. In addition, since the quantization error of each analog-to-digital converter is a constant value regardless of the resolution, if the number of analog-to-digital converters used is N, the error in the load that occurs during addition is FV Therefore, by adding the resolution of each analog-to-digital converter to the required minimum resolution fl- or more, and dividing the value after the addition by the resolution magnification, the value is the sum of the values. The quantization error can be directly reduced by using one analog-to-digital converter.

(Example) Hereinafter, a load cell scale of the present invention will be explained with reference to the drawings.

In FIG. 2, reference numeral 1 denotes a rectangular base made of aluminum or the like, and load cells 2a, 2b, 2c, and 2d are attached to the four corners of the base 1. And these load cells 2a, 2b2c,
2d is a substantially 8-shaped communication hole 3a3b that communicates between the side surfaces;
The communication holes 3 of each load cell 2a, 2b, 2c, 2+l are formed into a substantially rectangular parallelepiped shape with 3c and 3d.
a, 3b, 3c.

Two strange gauges 4a, 4b, 4c, and 4d are attached to the upper surface of the thin wall portion above 3d, respectively.
It is a donkey pal mechanism. On the other hand, these load cells 2
One end of the lower surface of the components a, 2b, 2e, and 2d is attached to a mounting base 5a, 5b, 5c, and 5d provided on the base 1, and the other end of the lower surface is an overload stopper 6a provided on the base 1.

6b, 6c, and 6d. Furthermore, protrusions 7L 7b, 7c, and 7d are attached to the other ends of the upper surfaces of the load cells 2a, 2b, 2c, and 2d. And protrusions 7a, 7b, 7c, 7d
The tip is open at the bottom and abuts on the inside of a tray 8, which is slightly larger than the base 1, and supports the tray 8 so as to be movable in the vertical direction.

The base body 1 also includes a storage case 9 in which electronic components and the like are stored.
is provided.

Furthermore, mounting stands 5a and 5b provided on the base 1.

5c and 5d have legs IhI whose height can be changed on the back surface.
Qb, IOc, and It'd are provided to hold the base 1 horizontally.

And these load cells 2a, 2b, 2c,
2d are amplification means 11a, flb, llc, such as operational amplifiers, respectively, as shown in FIG.
, lld, respectively, and these amplifying means 11a
, llb, llc.

11d is an analog-to-digital converter (A/D converter)
12a, 12b, 12c, 12d
These analog-to-digital converters 12a
, 12b, 12c.

12d is the analog-to-digital converter 12a, 12b of the CPU 13 such as a microcomputer;
, 12c.

An adder as an addition means to add the output of +2tl!・
1, and this adder 14 is connected to a divider 5 (as a division means for dividing by resolution), and this divider 15
is connected to storage means 16 for storing load values and the like. Further, this CPU 13 is connected to a keyboard 17 such as a numeric keypad and a display 18 as a display means.

Next, the operation of the above embodiment will be explained 7. First, the object to be tested is placed on the mounting plate 8, and each load cell Ia, Ib
The outputs of , Ic, and Id are connected to the operational amplifier l1a11.
b, Ilc, lid, and analog-to-digital converters 12a, 12b, 12c,
Analog to digital conversion is performed at IN.

Then, the adder I4 adds each value, the divider 15 divides by the resolution, and the load value is stored in the storage means 16.

Also, each analog/digital conversion Xl2a.

Load cells 2a, 2b, 2c, 2 converted from analog to digital by 12b, 12c, 12d
d is the relationship between the load and the digital output due to this load, as shown in FIG.

Here, for example, as in this embodiment, four load cells 2
Analog-to-digital converters 12a, 12b, 12c using a, 2b, 2c, 2d, respectively
, 12d, the variance of the dispersion addition method becomes S=a+b+c2+d', resulting in a variation that is J4=2 times or more than when one load cell is used. Therefore, in order to achieve the same variation as when using one load cell, analog-to-digital converters 2a, 12b, and 12c are required, respectively.
, 12d requires more than twice the resolution. for example,
When one analog-to-digital converter is used, and the rated load is 15 kg and the minimum measurable load is 0.5 g, the resolution is 1500010.530000. Therefore, when four analog-to-digital converters are used, if the resolution of each analog-to-digital converter is set to 60,000 or more, and division is also performed by twice the number, one analog-to-digital converter can be used. The variation can be suppressed to the same level as if it were.

In other words, since the quantization error of each analog-to-digital converter is a constant value regardless of the resolution, if the number of analog-to-digital converters used is N, the error in the load caused by addition is distributed addition. According to the method, it is multiplied by FT, so add the resolution of each analog-to-digital converter to be more than r lower than the required minimum resolution, and then add the value obtained by dividing the added value by the resolution magnification. By using this value, the quantization error can be improved to the value when one analog-to-digital converter is used.Furthermore, when calculating the price for weight, etc., input the unit price using the keyboard 17. , CPU] 3, and the weight and price are displayed on the display 18.

(Effect of the invention) According to the present invention, when N analog-to-digital converters are used, the minimum resolution of the analog-to-digital converter is /]- times or more as compared to when one analog-to-digital converter is used. By dividing by this multiple, the weight can be measured with the same accuracy even if N analog-to-digital converters are used as when one analog-to-digital converter is used. Highly accurate measurements can be made.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the load cell scale of the present invention, FIG. 2 is a perspective view of the same with the mounting plate removed, and FIG. 3 is a graph showing the output of the analog-to-digital converter. 2a, 2b, 2c, 2d--load cell,
12a, 12b12C, 12d - Analog-to-digital converter (A/D converter), 14... Adder as addition means, 15. Arithmetic unit as division means. Zunxia Station

Claims (1)

[Claims] (1) In a load cell scale that measures weight by converting the outputs of a plurality of load cells with a plurality of analog-to-digital converters and adding the digital outputs of these analog-to-digital converters with an adding means, A load cell scale characterized in that, when the number of digital converters is N, the resolution of the analog-to-digital converter is set to √N times or more, and is provided with a dividing means for dividing the added digital output by this multiple. .