JPS61288123A - Electronic scale - Google Patents

Abstract

PURPOSE:To remove the influence of an external electromagnetic wave with simple constitution by forming the whole or part of a case of a conductive resin material and connecting a scaling pan to the case electrically. CONSTITUTION:The whole of the case A is formed of a conductive plastic material in one body so that the case is at the same potential. An earth terminal is implanted in part of the case A and contacts short fiber of stainless steel mixed into the case A. Then, an insulator (g) is fitted between the scaling pan D and a load cell (a) to prevent a high frequency current which arrives at the pan D from flowing to a strain gauge stuck on the load cell (a) and a part where the high frequency current does not exert influence is connected to the pan D by a conductor L. Consequently, even if the pan D operates as an antenna, a high frequency current induced there by-passes the strain gauges and is transmitted to either the strain gauge nor a circuit board (b). Further, static electricity generated at the pan D by the loading of a charged body to be measured is transmitted to the case A and flows through an earth line connected to the case A and a power line.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electronic scale that eliminates the influence of external electromagnetic waves and prevents internal circuit failure due to charging of a weighing pan.

(Prior Art) FIG. 3 shows a perspective view of an electronic scale, and in the figure, A is a case of the electronic scale. The case A has upper and lower Al
, can be separated into A2 parts, and is made of a plastic molded product. At the top of case A, there are 5 objects to be weighed, such as products to be measured. A weighing pan is provided for placing the sample. The front of case A is provided with a keyboard section for inputting the product name of the object to be weighed or abbreviated numerical symbols representing the product name, numerical values, etc. into the electronic scale, and a display section for displaying the input values, weight, etc. There is. Furthermore, a specification plate P is attached to the rear of the case A. In case A, as shown in Figure 4, a load cell a for weight detection and an A/D converter and operational amplifier that convert the analog weight signal detected by load cell a into a digital value are used. There are provided a circuit board b on which an amplifier circuit, a low-pass filter, a diode, a resistor, a capacitor, etc. are disposed, and a circuit board on which a control device including a microcomputer (not shown) is provided. A weighing pan provided above the case A is fixed to the movable part of the load cell a with a screw e via a pan holder f.

(Problems with the prior art) In an electronic balance with such a configuration, (1) When a metal weighing pan or a pan holder is used, the incoming external electromagnetic waves are captured by the weighing pan, and this is transmitted from the weighing pan to the load cell a. For example, this may enter the circuit board and cause a measurement error, or noise components caused by this may enter the computer and cause malfunction.

(2) To deal with this, it is possible to interpose an insulator between the weighing pan and the load cell, but if the weighing pan becomes charged due to the loading of a charged object to be weighed, the static electricity Since there is no place to escape, sparks may occur between the pan and the case or between the pan and the worker, and this noise component may enter the circuit board somewhere and cause malfunction, or this may cause the circuit to malfunction. Failures may occur in elements, etc.

There were other problems.

For this reason, conventionally, (1) Apply conductive paint to the inside of the case.

(2) Shield the entire circuit with a metal body.

etc., to address the above inconvenience. However, solution (1) has the disadvantage that the applied conductive paint is likely to peel off, and the conductive paint is oxidized, increasing the resistance value and reducing the shielding effect. In addition, the method (2) has the disadvantage that the structure becomes complicated and the manufacturing cost increases.

(Purpose of the Invention) The present invention aims to solve the problems of the prior art, and has a simple configuration that eliminates the influence of external electromagnetic waves and prevents failure of the internal circuit due to charging of the weighing pan. It provides electronic scales.

(Summary of the Invention) The electronic scale of the present invention surrounds at least a weight detector and an electronic circuit for processing detection signals thereof in a case, and connects the weight detector to the upper surface of the case through a communication port provided on the upper surface of the case. An electronic scale that combines a weighing pan and the weight detector, wherein the case is entirely or partially made of a conductive resin material, and the weighing pan and the case are electrically connected. It is characterized by:

(Function) Since the weighing pan and conductive case are electrically connected,
Electromagnetic waves arriving around the electronic scale are completely shielded by the weighing pan and case, and do not affect the inside.Also, since the weighing pan is electrically connected to the case, even if the weighing pan is charged, it will not affect the inside. Static electricity is discharged through the case and the power ground connected to the case, and no spark occurs as in the conventional case.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of an electronic scale embodying the present invention. Note that the same reference numerals are given to the same components as in the conventional example, and detailed explanation thereof will be omitted.

In the present invention, the entire case 8 is integrally formed of a conductive plastic material so as to have the same potential.

The conductive plastic material is made of well-known moldable plastic materials such as ABS resin and polycarbonate resin, and as shown in FIG. 2(a), some of them include:
Stainless acid short fibers F having a thickness of about 5 to 25 microns are mixed. The stainless steel and stainless steel wires are intertwined and in contact with each other, so that the entire case A becomes electrically conductive. Part of case A includes the i-th
As shown in detail in Figure (a), a ground terminal E is implanted, and this ground terminal is in contact with a short mmF of stainless acid mixed in the case A. Therefore, if the ground terminal E is installed and grounded, the entire case A will be at ground potential.

Further, inside the case A, a stud S for assembling the upper and lower cases Al and A2 is provided. This stud S
A knurling is cut at the root of the terminal, and this part, like the ground terminal E, is in contact with the stainless acid short fibers F. Note that when the upper case A1 is attached to this stud S, it comes into contact with the ground potential portion thereof.

The conductive case A can also have a structure in which the stainless acid short fibers F are gathered in the center as shown in Figure 2(b), or it can have a structure in which the stainless acid short fibers F are gathered in the center as shown in Figure 2(C). It is also possible to have a structure in which woven fabric FF woven from stainless steel m fibers is gathered in the center. In still other embodiments, carbon powder may be mixed into the plastic forming the case A, or carbon fibers may be mixed in the same manner as stainless steel fibers to make the entire case conductive. Alternatively, the ground terminal of the DC power supply and the short fibers F in the case A may be connected so that the static electricity in the case A flows to the power supply line.

An insulating material g is installed between the metal weighing pan and the load cell to prevent external electromagnetic waves (high frequency current) arriving at the weighing pan from flowing to the strain gauge attached to the load cell, and to prevent the high frequency current from flowing to the strain gauge attached to the load cell. Location 1 that does not affect the strain gauge: For example, connect the opposite side of the load cell to which the strain gauge is attached and the weighing pan with a conductive wire. As a result, even if the weighing pan acts as an antenna, the high frequency current induced therein avoids the strain gauge and does not flow to the strain gauge or the circuit board. Furthermore, static electricity generated on the weighing pan due to the loading of a charged object to be weighed is transmitted to the case, and actually flows through the ground wire and power supply line connected to the case, so there is no possibility of damage between the weighing pan and the case or circuit board, etc. No spark occurs.

In the above embodiment, the weighing pan is made of metal, but it may also be made of plastic, or it may be made of conductive material by mixing stainless fibers, carbon ms, or carbon powder as described above. It goes without saying that a weighing pan with a sterile structure may also be used.

(Effects of the Invention) As explained above, according to the present invention, all or part of the case is formed of a conductive resin material, and the weighing pan and the case are electrically connected. It is possible to prevent measurement errors from occurring due to the influence of external electromagnetic waves, and it is also possible to prevent sparks due to charging of the weighing pan and the occurrence of internal circuit failures due to this.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of the present invention, FIG. 2 is a partial sectional view showing essential parts of the present invention, FIG. 3 is a perspective view of a conventional example, and FIG. 4 is a configuration diagram of a conventional example. a...Load cell, b...Circuit board, A...Case, D...Weighing pan, e...Screw, f...Dish holder,
g...Insulating material. Patent applicant: Ishida Kouki Seisakusho Co., Ltd. Representative: Patent attorney Minoru Tsuji Road tJsha
Circuit board Figure 2 ((2)

Claims (7)

[Claims] (1) At least a weight detector and an electronic circuit that processes its detection signal are surrounded by a case, and the weighing pan on the top of the case and the weight detector are connected through a communication port provided on the top surface of the case. What is claimed is: 1. An electronic scale comprising: an electronic scale in which all or part of the case is made of a conductive resin material; and the weighing pan and the case are electrically connected. (2) The electronic scale according to claim (1), characterized in that the weighing pan and the weight detector are coupled via an insulator. (3) The electronic scale according to claim (2), wherein the weighing pan is made of metal. (4) The electronic scale according to claim (1) or (2), wherein the weighing pan is made of synthetic resin. (5) The electronic scale according to claim (2), wherein the weighing pan is made of conductive synthetic resin. (6) The electronic scale according to claim (1) or (5), wherein the conductive synthetic resin is a conductive synthetic resin mixed with metal fibers. (7) The electronic scale according to claim (1), wherein the case is connected to a power supply ground.