附录：英文技术资料翻译
Journal of Jiaozuo Institute of Technology (Nstursl Science),
Vol.20,No.4,Jul.2001
英文原文：
The development of portable digital balance
GUO San-ming'  Z H ENG J un-zhong
(Dept,of Electri.Eng .of JIT,Jiaozuo 454000,China)
Abstract: More attention has been paid on the development of the portable digital balance with commercial worth since the usual measurers have been unpopular such as pole balance spring balance and some others .The scheme of the portable digital balance with high performance and low cost is put forward. The ideas for the signal process circuit is introduced and the specie hardware chart is made. The key parts of the weigh sensor elastomer are specified. Moreover the problems to deal with the current and the improvement on the accuration have been solved.
Key words: digital balance; elastomer; power amplifier; measurement range conversion; electric resource
CLC; TH 715.1 +93 Document Code: A literature number 1007 -7332 (2001) 04-0269-04
0 Introduction
Development of science and technology, the weighing technology put forward higher requirements, especially micro-processing technology and sensor technology, tremendous progress has greatly accelerated this process. Currently, electronic scales used in commercial sales have been quite common, but all kinds of electronic scales are widely used in the market, there are significant limitations. These electronic scales large volume, high cost, need for frequency AC power supply, and can not carry. Popular portable
electronic weighing scales on the market, or they use a rod to the spring compression, tensile deformation of the spring balance to achieve, such as metering, measurement error is large, more than once spring elastic limit, it will generate a lot of errors, as well as damage to the rod type scales are currently going out of the metering equipment, therefore, a miniaturized, can be replaced in the future development of universal rod scales electronic scales by the people attach great importance to
weigh翻译design a lightweight, easy to carry, accurate measurement, intuitive readings civilian electronic scales imminent.
This product is fully electronic circuit design, fully taking into account the advantages of various types of electronic scales, and small and portable, measurement error is small (1%), reliable / low prices on the civilian market has good prospects for use.
1  System Principles
Portable electronic scale system shown( Figure 1), which consists of sensors, amplifiers, range conversion circuit, A / D converter and a display / power supply circuit and the like.
Strain gauge sensor element consisting of a resistor, the weighing weak signal, the precision of the differential amplifier, two stages (0~2Kg, 2~10Kg) automatic conversion range, the A/D converter, said amplified re-converted into an analog signal to a digital liquid crystal display (LCD) display, the processing circuit power supply voltage into the battery power supply voltage level required for the type of each unit circuit.
2  load cell selection and design
In the electronic scale system , the sensor is the most critical component is also part of the design of electronic scales difficult to deal with , its performance directly
determines the accuracy of electronic scales . Small -scale load cell structure , type and more categories . In order to make the load cell has good linearity , strong input sensitivity and strong resistance to lateral load force , we have adopted a two-hole parallel beam load cell [1] ( Figure 2 ),as the use of domestic hard aluminum alloy LY12 elastomer material, the elastic hysteresis and creep is small, the small -scale load cell, the storage of this material is larger than W, elastic modulus is small (about 1 / 3 of steel), the manufacture of small the load cell weighing scale , and the ideal material.
Working principle of the sensor is : When the sensor is subjected to external loads prole of the upper and lower beams parallel elastomer elastic deformation / paste in a parallel beam of four strain gauges R1~ R4 consists of bridge output voltage is generated with linearized external load increment p , p can know the size of the external load.
Size of the sensor according to the maximum range of the elastic element may be primarily determined detection point ( peak stress ) section thickness h1,, to determine the form and size of the opening , the sensor sensitivity is generally require (1.5 ~ 2) mV / V range, the full-bridge The output voltage U 0.
As                          0CC U S U ε=,
Where:  S-strain gauge sensitivity factor;
U C C  - -for the bridge voltage
ε-Detection Point (strain gauge affixed at) strain,
S U U CC /)/(0=ε
Also      1/P M E W ε= ,
Where:  Mp-detection point bending moment;
E -modulus of elasticity of the  material;
W1-detection point flexural modulus;  .)6/(211bh l W =
Beacuse    ),2/(:)2/(:max L l M M P =  (Similar triangles);
So          ,4/)4/)(/(pl pL L l M P -=
Where:  b -elastic  element  width;
h1-sectional thickness detection point ;
Mmax = pL/4- maximum bending moments at both ends of the elastic element ;                p-Maximum weight;
l-double hole center distance;
L-length of elastomers
Can  push              164pl h Eb
ε= Open hole diameter 12h φα=-，2()/2h L l φ=--
The stiffness ratio  α
L h h K 312)(= . This value can be used as calibration values  estimated elastic stiffness is adequate. Size elastomer determined according to the above principles, its processing by
conventional technology standards, through the heat out of the library , the opening line cutting , grindi
ng and other processes required by conventional patch
3 amplifier circuit design processing several problems
(1)  Power : This e- weighed 2 on the 5th ordinary zinc-manganese batteries (3V) or rechargeable battery (2.4V) power supply. For each level of the supply voltage circuit for this is not enough , so the choice of switching to Boost Regulator Manifold TL499A for power conversion ( Figure 3 ).
The output voltage of the regulator TL499A range of up to 2.9 ~ 30V, output current of 100mA, the required input voltage range of 1.1 ~ 10V. TL499A the battery voltage up to 15V, 7.5V and then get a symmetrical voltage output through the op amp. (2) Reduce the influence of the equivalent offset voltage measurement accuracy ; bridge output signal is superimposed on a high voltage DC supply mold weak signal , you should first ensure that the power bridge to get a high degree of stability , constant current bridge uses circuitry as shown in ( 4 ) below.
By the A1, R5, R6, R1 constitute a constant current source circuit for providing a high degree of stability bridge power circuit . R1-R4 constituting the detection resistance strain gauge bridge force due to the action of the force to deform the elastic body , leaving a corresponding change in strain gauge resistance , thereby weak bridge output voltage signal proportional to the force by the elastic bo
dy , Rp is zero potentiometer to adjust the bridge output to zero. A2-A5 and peripheral components of the differential amplifier . The circuit has an input impedance (300-500mΏ) high , high common mode rejection ratio (110DB). Input offset voltage (20uv) and offset voltage drift (0.25-10uv / ℃) small features, ideal for the bridge amplifier circuit form . Circuit is divided into two , the first stage consists of A2, A3 , thereby to improve the input impedance of the amplifier circuit , the second stage by the A4, A5 constitute a differential amplifier , seeking an exact match to A4 external resistor , while lower gain circuit has guaranteed small offset voltage , Rw number tune the gain of the amplifier.
(3) Achieve scale transformation , the electronic scale range is divided into two ranges , the first range 0-2Kg, second range 2-10Kg, automatic conversion range from

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