Journal of Science & Technology 101 (2014) 096-099 An Analog Divided Method Using Analog ADC for Conditioning Circuit Nguyen Thi Lan Huong Hanoi University of Science and Technology, No I, Dai Co Viet Str., Hai Ba Trung, Ha Noi, Viet Nam Abstract Ivlany measurement circuits use divider of two analog signals, for example temperature measurement circuit using resistive bridge; deformation measurement bridge Analog divided circuit is a highly difficult and complex to design This paper presents an analog divided method to obtain digital results by using Analog Digital Converter (ADC) The method is applied to weighting equipment base on load cell (SIWAREX) of SIEMENS Results are then compared with tradition method to assert really nght ofmettiod Key word Divider, ADC, Load cell Introduction SUPPLY VOLTAGE In this paper, a study of advantages and disadvantages of using ADC as divided circuit The divided using ADC circuit is not presented and analyzed in documents or books on the measurement that has only been menhoned m same of application notes [1], The author presents clearly advantages of the method Results of the experiments show that the proposed method out-performed traditional one The Method Using Converter ADC as a Divided Circuit Fig.l The importance signals of ADC An ADC output value is calculated hy the formula _U^ (1) q In this equation Ui i-'i is la an ait input l u ^ u i voltage; vuimgc, q IS a last significant bit In ADC the q value is derived from the reference voltage Divided circuit two analog signals are widely apphed m the measurement circuit because of its unification characteristic For example, the problem of load cell is often used for 1-way circuits (for Wheatston - [2]) with one or two actives branch Here we analyze a arm bridge circuit works as follows: Thus, the output N of an ADC is a number proportional to the ratio of the input voltage and the reference voltage However, the ADC reference voltage IS interpreted as a constant voltage, both voltage regulators inside and outside ADC, Hence, the output value of the ADC is only a varied number of input voltages For this scheme an approximate one can calculate In formula (I) if Um voltage, reference voltage Vref are considered as two analog variables, we will have N as a percentage of the ratio of two voltage signals That means ADC is divider by two analog signals Uin and Vref This divider has result is numeric This is advantage compare with another analog divider ' Corresponding aulhor: Tei: (-1-84) 914 949.697 Email; huong nguyenthilan@hust,edu.vn AU = R ^.r Aff (2) ^cc Accordmg to the above formula, we have the resistor raUo is considered as the output voltage of the bridge considered to bridge the supply voltage is constant Therefore result is measurement of diagonal voltage, as it would need to ensure that errors of supplier are small From these observations, there is a more accurate method if we put signals (and the diagonal voltage supply) to the input of the ADC and the standard sources, such as the value of the ADC output IS proportional to the second ratio of input voltage and power supply This model has been used in [2] without clearly identified its advantages Journal ofScience & Technology 101 (2014) 096-099 R4 r / y \y R3 • • " ^ ''°^Rr^R4''«-RZ \ S^ R2 \ y R1 RZ R4 ' R3 AT BALANCE Vo = IF ^ = V Fig Wheastone Bridge Experiment and Results Compare In order to compare two methods, the systems are implementing based on Load cell SiwaREX of Siemens The design of the system is illustrated in the Fig 3, Expenments for measuring circuit work in two modes, the default mode when turn the mode used ADC normally In this mode, the reference voltage is the standard voltage, independent of the stability voltage of the sensor resistance The Second mode of experiment is ADC as divider The value received by the ADC conversionThe conditioning of Load cell illusfrated in Fig 2, With bridge measuring circuit the branches stamped compensation of the sensor as shown in Fig about SIWAREX R BB [3, 4], differential voltage output value of for the branch: U^.AR CT- (3) UT is the differential output voltage value of the resistive two branches UN is power supply In the second mode The voltage output of coditioning circuit connect lo the input of ADC, and the power supply connets to AREF pin (reference pin of ADC), The program is written in C programming language using software Code Vision for microprocessor ATMEGA8535 This microprocessor has ADC inside, which mode of reference voltage The algorithm is illustrated in the follow Fig Fig Signals of Load cefl Comparisons of experimental results are shown in the following table Survey the independent of output in changing input values (power supply) With 50 Kg load, voltage feed circuit to change the sensor The values of voltage divider obtained to make comparisons Standard equipment Power Supply Kikusui PMC35-3 is used to supply for the circuit The results were illustrated in dependence of the value of the sensor output voltage changes in difference modes Table Experimental results for testing dependency of output to power supply in difference in modes Voltage (V) 4,70 IslMode 47,45 (Kg) 2nd Mode 49.99 (Kg) 4,75 4,80 4,85 4,90 4,95 5.00 47,98 48,28 48,74 49,15 49.57 50,01 50,01 50,02 50,00 50,00 50.01 50,00 From the experiment results in Table I we had foilowmg conclusions; When there is a slightly change of power supply (0.05 V), there would be a sweeping change in the first working mode While, with the divided mode, the reference voltage for sensor power supply (second mode), the measurement results are almost no changed When usmg mode I, to ensure the stability and accuracy of measurement results, the power supply of sensor required stabilizing, but we can change the voltage feed to increase the output voltage value Journal of Science & Technology 101 (2014) 096-099 Raising the voltage range may be greater than supply voltage for ADC When using second mode, the results are accurately measured even when the sensor power supply is not ( stable In fiirther, the supply voltage for die sensor in ^'"s ""ode is not higher than supply voltage for ADC, START j Fig Algorithm flowchart of experiments Journal ofScience & Technology 101 (2014) 096-099 Conclusion This method is applied to the power supply circuit with high accuracy The experimental results prove the conectness of the method Moreover, one of advantage is result of divider is numerical, wich easy to use in digital systems as in microprocessor or microcomputer This method only apply for ADC has outside reference Using ADC for divided circuit is an efficient method of conditioning [I] Data sheet ICL 7107, MAXIM, 2000 [2] Bridge circuits, Walts Kester, Analog Device Company, 2002 [3] Handbook of modem sensor s (physics Design and Application), Jacob Fraden, Springer, 2004 [4] SIWAREX weighting SIEMENS 2002 system Catalog ... only apply for ADC has outside reference Using ADC for divided circuit is an efficient method of conditioning [I] Data sheet ICL 7107, MAXIM, 2000 [2] Bridge circuits, Walts Kester, Analog Device... The voltage output of coditioning circuit connect lo the input of ADC, and the power supply connets to AREF pin (reference pin of ADC) , The program is written in C programming language using software... the mode used ADC normally In this mode, the reference voltage is the standard voltage, independent of the stability voltage of the sensor resistance The Second mode of experiment is ADC as divider