JPH08233636A - Load cell scale - Google Patents

Abstract

PURPOSE: To remove noise components induced from a bridge circuit despite of a simple structure by connecting earth faces of penetration filters to which a strain sensor is connected, to an earth pattern of the circuit substrate. CONSTITUTION: A plurality of penetration filters 16-21 held by a circuit substrate 11 and a plurality of strain sensors 6-9 located on a load cell main body 1 are connected each other via a conductive mat 14 and a lead wire 26 so as to form a bridge circuit. In this case, the earth faces of the filters 16-21 are connected and fixed to a conductive earth pattern 13 formed on the substrate 11 by solder so that an electric wave as a noise component induced from the bridge circuit can be released from the earth faces of the filters 16-21 via the earth pattern 13. And connection of the earth faces of the filters 16-21 for connecting between the sensors 6-9 and the substrate 11 to the earth pattern 13 can remove noise and simplify and minimize the structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load cell balance for weighing an object by converting a load into an electric signal.

[0002]

2. Description of the Related Art Conventionally, a load cell body having a plurality of flexible portions is provided between a fixed portion fixed to a part of a balance main body and a pressure receiving portion to which a tray is connected. A plurality of strain sensors fixed to each of them are connected to form a bridge circuit, voltage from the power supply is applied to the input side of this bridge circuit, and the flexible part of the load cell body is distorted according to the load applied to the pressure receiving part. There is a load cell scale which is distorted together with a sensor and measures the weight of an object applied to a pressure receiving portion by the output of a bridge circuit according to the strain amount of the strain sensor at this time.

[0003]

Radio waves are induced from the bridge circuit of the load cell balance, and the radio waves are conducted as noise to the circuit elements on the circuit board, which affects the characteristics of the load cell balance. In order to remove this noise, there is a problem that the structure becomes complicated and the load cell scale becomes large.

[0004]

According to the present invention, there is provided a load cell main body having a plurality of flexible portions formed between a fixed portion fixed to a part of a balance main body and a pressure receiving portion to which a tray is connected. A plurality of strain sensors fixed to each of the flexible parts, a plurality of feedthrough filters held on a circuit board, a plurality of the strain sensors and a plurality of feedthrough filters are connected, and an input side is connected to a power supply and output A bridge circuit whose side is connected to the arithmetic unit and a conductive ground pattern formed on the circuit board while being connected to the ground surface of the feedthrough filter.

[0005]

Since the ground surface of the through filter to which the distortion sensor is connected is connected via the ground pattern of the circuit board, it is possible to remove the radio wave induced from the bridge circuit.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. In FIG. 1, reference numeral 1 is a load cell body made of a metal material. The load cell main body 1 is provided with a fixed portion 2, a pressure receiving portion 3, and a deformed opening 4 that is largely opened between the fixed portion 2 and the pressure receiving portion 3. Fixed part 2
An attachment hole (not shown) fixedly attached to the base (not shown) of the balance main body is formed on the lower surface of the, and a plate (not shown) for placing an object to be weighed is provided on the upper surface of the pressure receiving portion 3. A mounting hole 3a (see FIG. 2) to be connected is formed. As shown in FIG. 1, the odd-shaped opening 4 has a shape in which two adjacent elliptical holes are made to communicate with each other at the central portions on the adjacent sides, and by forming the odd-shaped opening 4, the upper surface and the lower surface of the load cell body 1 are flexible. Two parts 5 are formed. Strain sensors 6, 7, 8 and 9 are fixedly arranged on these flexible portions 5.

A metal supporting plate 12 holding one end of a circuit board 11 is fixed to the side surface 10 of the load cell body 1 on the side of the fixing portion 2. The circuit board 11 holds various circuit elements (not shown), and
A conductive ground pattern 13 occupying a region (a region shown by diagonal lines) surrounding the circuit elements and a plurality of pairs of conductive mats 14 facing each other with a part of the ground pattern 13 therebetween are formed. There is. The earth pattern 13 is connected to the support plate 12 by, for example, a metal screw 15 for attaching the circuit board 11 to the support plate 12, and the support plate 12 is connected to the scale main body described above via the load cell main body 1. It is grounded to the base.

Further, both ends of a plurality of feedthrough filters 16 to 21 are connected to the conductive mat 14 formed in pairs on the circuit board 11. That is,
As shown in FIG. 4, these feedthrough filters 16-21
Is composed of a metal square tube portion 22, a conductor 23 penetrating the square tube portion 22, and terminal portions 24 connected to both ends of the conductor 23, and has a function of a capacitor. . The penetration filters 16 to 21 as described above are provided in the terminal portion 2
4 is connected and fixed to the conductive mat 14 on the circuit board 11 by soldering, and the ground surface 25 (one surface of the central portion of the square tube portion 22) is connected and fixed to the ground pattern 13 by soldering.

A bridge circuit 27 is formed as shown in FIG. 3 by connecting the strain sensors 6 to 9 to the predetermined conductive mat 14 via lead wires 26 and the like. More specifically, both ends of the strain sensor 6 are connected to the through filters 16 and 17, both ends of the strain sensor 7 are connected to the through filters 17 and 18, and both ends of the strain sensor 8 are connected to the through filters 19 and 20. Both ends of the strain sensor 9 are connected to the through filters 20 and 21. Further, the input side of the bridge circuit 27 is a through filter 1
The bridge circuit 2 is connected to the power supply 28 via
The output side of 7 is connected to the circuit unit 29 through the through filters 16 and 19 and the through filters 18 and 21. The circuit unit 29 includes an amplifier 30 that amplifies the output (analog signal) of the bridge circuit 27 and an A / D converter 31 that converts the output to a digital signal. Furthermore, the circuit section 29
Is connected to an arithmetic unit (not shown) for arithmetically processing the signal from the circuit unit 29 into the weight value of the object to be weighed, through the same penetration filter as the penetration filters 16 to 21.

In such a structure, the load of the object placed on the placing plate is transmitted to the pressure receiving portion 3, and the flexible portion 5 is distorted together with the strain sensors 6-9. The electric signal output from the bridge circuit 27 according to the distortion amount at this time is transferred to the circuit unit 29.
The weight of the object is measured by amplifying it and converting it into a digital signal, and subjecting the digital signal to arithmetic processing in the arithmetic section. In this case, as shown in the plan view of FIG.
Since the circuit board 11 is separated from the pressure receiving portion 3 and the flexible portion 5 of the load cell body 1, the circuit board 11 does not hinder the strain operation of the load cell body 1.

Further, during such measurement, the electric wave as a noise component induced from the bridge circuit 27, the ground surface 25 of the through filters 16 to 21, the ground pattern 13 on the circuit board 11, the support plate 12, the load cell body. 1 to the base of the balance body. Furthermore, since the ground pattern 13 surrounds various circuit elements arranged in the central portion of the circuit board 11, these circuit elements can be shielded from external noise. Further, since the circuit unit 29 and the arithmetic unit are also connected via the through filter, the influence of noise between them can be eliminated.

Further, the strain sensors 6 to 9 and the circuit board 11 are arranged.
The ground plane 25 of the through filters 16 to 21 for connecting with
Since the noise can be removed only by connecting to the ground pattern 13 on the circuit board 11, it is possible to simplify and downsize the structure for removing the noise.

[0013]

As described above, according to the present invention, a plurality of feedthrough filters held on a circuit board and a plurality of strain sensors on the load cell body are connected to form a bridge circuit, and the feedthrough filter is grounded. Since the surface is connected to the conductive ground pattern formed on the circuit board, radio waves as a noise component induced from the bridge circuit can escape from the ground surface of the feedthrough filter through the ground pattern on the circuit board. Thus, the influence of noise can be removed. Further, since the noise can be removed only by connecting the ground surface of the feedthrough filter connecting the strain sensor and the circuit board 11 to the ground pattern on the circuit board, the structure for noise removal can be simplified and the size can be reduced. Can be realized.

[Brief description of drawings]

FIG. 1 is a side view showing an embodiment of the present invention.

FIG. 2 is a plan view.

FIG. 3 is a circuit diagram showing a configuration of a bridge circuit and connection with the outside.

FIG. 4 is a side view showing a structure of a feedthrough filter and a connection state to a circuit board.

[Explanation of symbols]

 1 load cell main body 2 fixed part 3 pressure receiving part 5 flexible part 6-9 strain sensor 11 circuit board 13 earth pattern 16-21 penetration filter 25 earth surface 27 bridge circuit 28 power supply

Claims (1)

[Claims] 1. A load cell main body in which a plurality of flexible portions are formed between a fixed portion fixed to a part of the balance main body and a pressure receiving portion connected to a loading tray, and the load cell main body fixed to each of the flexible portions. A bridge in which a plurality of strain sensors, a plurality of feedthrough filters held on a circuit board, a plurality of the strain sensors and a plurality of feedthrough filters are connected, an input side is connected to a power supply, and an output side is connected to a calculation unit. A load cell balance comprising a circuit and a conductive ground pattern formed on the circuit board while being connected to a ground surface of the feedthrough filter.