Slovak University of Technology in Bratislava Institute of Information Engineering, Automation, and Mathematics PROCEEDINGS

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1 Slovak niversity of Technology in Bratislava Institute of Information Engineering, Automation, and Mathematics PROCEEDINGS th International Conference on Process Control 00 Hotel Baník, Štrbské Pleso, Slovakia, June, 00 ISBN Editors: M. Fikar and M. Kvasnica Skočík, P., Hruška, F.: New Aspects of Small Electric Power Measurement, Editors: Fikar, M., Kvasnica, M., In Proceedings of the th International Conference on Process Control 0, Štrbské Pleso, Slovakia,, 00. Full paper online:

2 th International Conference on Process Control 00 June, 00, Štrbské Pleso, Slovakia Po-We-, 0.pdf NEW ASPECTS OF SMALL ELECTRIC INPT POWER MEASREMENT P. Skočík and F. Hruška Tomas Bata niversity in Zlín, Faculty of Applied Informatics Nad Stráněmi, 0 0 Zlín, Czech Republic fax: 0 0 and skocik@fai.utb.cz, hruska@fai.utb.cz Abstract: The paper is focused on the small electric input power measurement for research and study of material machining. The requirement is to have the measurement with high accuracy and sensitivity. The commercial devices for measuring the electric input/output power are available only for wide ranges. Therefore, an analog device for electric input power measurement was developed. The new demand is to redesign the circuit for enhancing the sensitivity. Measurement of high electric input power values is changed to the measurement of their differences with reference value. The device consists of analog operational amplifiers and analog multiplier unit of effective electric current and voltage. Keywords: effective input power, low input power, input power difference. INTRODCTION The device for measuring the low electric power was constructed to solve a specific problem of polymer materials machining. It helps to prove the material suitability for this process. The main parts of the process are compared during the dynamic machining, e.g. cutting resistance, gyroscopic moment or power requirement of cutting engine. Generally, there are two possibilities how to determine cutting resistance. It is possible to take advantage of the exact understanding of the system. Then analytical dependences can be used. Second option is usage of more accurate indirect method based on measuring the power requirement of the cutting machine. The cutting force can be determined from this requirement after some mathematical operations. This is one example why to measure small electric effective power. Naturally, engineering practice knows quite large number of special applications dealing with the same problem how to measure small electric effective power. There are situations when commercial measuring devices cannot be used e.g. dynamic and static watt-meters. They are usually unsuitable due to their wide range and small accuracy. On the contrary, this measurement requires high accuracy and sensitivity. CIRCIT DESIGN The designed circuit for indirect cutting resistance measurement is based on simple balance equation. Total electric input power P c is equal to sum of power lost in drive unit P p and power spent for cutting P o (Hruška et al. 00). P P P k.. I.cos () c p o where: k conversion constant (-), effective value of supply voltage (V), I effective value of current (A), φ phase shift (rad). Electric input power can be obtained from equation () if the input voltage, current I and phase shift φ are measured. Proposed solution is shown in Fig.. The input phase voltage,ef and current I,ef go through multiplier into effective-value to DC-voltage conversion unit and then into output amplifier. The output value is unified signal out in range from 0 to0 V DC. This output voltage is proportional to the alternate electric effective power. Phase shift is omitted in this method (Hruška et al. 00).

3 th International Conference on Process Control 00 June, 00, Štrbské Pleso, Slovakia Po-We-, 0.pdf,ef I,ef Voltage sensor Current sensor a b Multiplier Effective a. b out value amplifier conversion Fig.. Block circuit diagram for small electric input power evaluation Scanning and amplifying of electric current and voltage effective values is shown in Fig.. This figure demonstrates the impedance match and separation via small transformers and amplification via operational amplifiers. Single-phase electric current flows through the supply wire which cause voltage decrease in shunt resistor. This sinusoidal alternate power supply voltage is separated, subsequently transformed via transformer TR I and connected to the amplifier. It provides voltage equal to the value of effective electric current I ef (Hruška et al. 00). AD is a high precision analog multiplier. The mathematical function of the circuit is: W ( X X ).( Y Y ) Z () 0V Conversion of the effective value after the multiplication is depicted in Fig.. effective value is given by: Y s T y. dt () 0 T For the harmonic signal it can be computed from the equation: Ys Y () max The conversion in analog methods is usually realized with circuit containing operational amplifiers. Analog converter for effective voltage values (Fig. ) transforms values of alternate voltage s into direct value o. However, this conversion is highly inaccurate. Fig.. The circuit for effective voltage and current measurement and small electric power input evaluation Similar method is used to connect additional voltage measuring part. Separation and impedance match is again designed via transformer TR and circuit with operational amplifier which produces voltage ef proportional to measured variable. The circuit ADJN from Analog Devices was used as the multiplying unit for analog values. The principle of this integrated circuit can be seen in Fig.. X X Y - Y - /0 x - Fig.. Integrated circuit AD V s W Z -V s Fig.. The circuit for effective values measurement CIRCIT FOR SMALL INPT POWER MEASREMENT REVISION The design of the circuit revision is based on the reconstruction of the original circuit (Skočík et al. 00) for small electric input power measurement. Results from measurements on the former circuit showed the suitability of the method for small electric input power measurement. The positive features are linearity, acceptable sensitivity and repeatability of measurements. However, there are also disadvantages such as: part of the measurement is using bridge connection and rectification which may not produce the value of ef, resistor shut is heated up extremely, small output range (from -0, to 0,V), the whole range /- 0V is not used, wide difference in the range 0-00 W. These negative points were the reason for the construction changes in revision. This new version of the circuit is shown in Fig.. It was also published (Skočík et al. 00). 0

4 th International Conference on Process Control 00 June, 00, Štrbské Pleso, Slovakia Po-We-, 0.pdf Lin Lout N Rb TR M TR TR R C R R R0 C0 R OZ D D C C R C R R R R D D0 OZ OZ C LM LM R R R R0 Fig.. Circuit diagram revision for difference of small electric input power measurenent D R C V -V D OZ C C R R R R OZ R R R OZ /0V OZ P R R P OZ C OZ Pout The proper function of the integrated circuit was verified by developing and constructing the testing circuit (Fig. ) and measuring in laboratory environment. The results from the measurement are shown in Table. Because the circuit is not availbale in Micro-Cap, it was replaced by the mathematical function..k V IN RMS 0 uf 0.uF 0.uF uf /-V DC VERIFICATION AND REDESIGN OF THE CIRCIT REVISION The program environment Micro-Cap, which serves for the electronic circuit analysis, was used for the verification. The simulation was focused on verification of the circuit parts for measurement of effective values. These parts are highlighted in Fig.. The circuit for current measurement (block number ) and voltage measurement (block number ). The simulation was performed for both parts separately. Results from the simulation showed that the output is not the voltage/current effective value, but only the rectified one. Due to this fact, both blocks ( and ) need to be reconstructed and replaced by different circuits. The redesign of the mentioned parts can be seen in Fig.. The parts from Fig. were replaced by the integrated circuit (Analog 00). This circuit transforms the harmonic signal to its effective value. Fig.. Scheme of the testing circuit The function of the was verified for the sine wave, square wave and triangular wave of the input signal with 0 Hz frequency. It is necessary to underline, that the input signal in the following tables represents the amplitude of the signal and not the effective value. Further, the input signal to the is in range from 0. to.0 V AC. Assumed utilization of the circuit revision with is for the sine wave with 0 Hz frequency. Therefore, the table is presented for wider measurement range than the tables and. Multimeter Metex was used for the comparison measurement. The effective values from and were compared with the theoretical value. Their absolute Δ and relative δ errors are again shown in Table. Some chosen values from the measurement of square and triangular waves are shown in tables and for the illustration. Lin Lout N Rb TR M TR TR R C R R R C0 R OZ D D VIN RMS C C R C 0 R R CIN C C CAV C LM LM R C V -V VIN RMS C C 0 R R R R CIN C C CAV R R R OZ /0V Fig.. Revision of the circuit for difference of small electric input power measurenent OZ P R R P OZ C OZ Pout Table. Effective values for sine wave ETC M 00 0,, 0, 00 0,,, 00, 0,, 00,,, 00,,0, 00,0,0, 00,0,0,0 00,0,0, 00,0,0, ,0 0,0 0, 00,0,0, 00,0 0,0, 00,0,0, 00,0,0, 00 0,0 0,0 00, 00,0,0,

5 th International Conference on Process Control 00 June, 00, Štrbské Pleso, Slovakia 00,0,0 0, 00,0,0, 00,0,0, ,0,0, Δ Δ δ δ 0,, 0,, 0,, 0,, 0,,0 0,, 0,, 0, 0, 0, 0, 0, 0,, 0, 0, 0,,0 0,0 0, 0,0,, 0, 0,,, 0, 0, 0,, 0, 0,, 0, 0, 0,, -, 0, -0,, -, 0, -0,, -, 0, -0,, -, 0, -0,, -, 0, -0,, -, 0, -0,, -, 0, -0,, -0, 0, -0, 0, -0, 0, -0, Table. Effective values for square wave ETC M 00,0,0 00,0 000,0,0 000,0 00,0 0,0 00,0 000,0 00,0 000,0 Δ Δ δ δ,0,0 0, 0,,0,0 0, 0,,0 -,0 0, -0,,0 -,0 0, -0, CONCLSION This contribution was focused on the verification and reconstruction of the circuit for difference of small electric input power measurenent. The main problem with effective value of AC volatge to DC voltage conversion was eliminated. The new path for further research and development of the device was opened. REFERENCES Po-We-, 0.pdf Hruška, F. and I. Lukovics (00). Dynamická obrobitelnost polymerních materiálů. In: VI. Mezinárodná vedecká konferencia Strojárska technológia 00. Súľov, Slovakia : september 00, ISBN Skočík, P. and F. Hruška (00). Analog measurement of electric power / Indirect measuring of machinability. In: Process Control 00. Štrbské Pleso, Slovakia :. 0. June 00, pp., ISBN Skočík, P. and F. Hruška (00). Reconstruction of measure device of electric effective power. In: th International Carpathian Control Conference 00. Rožnov pod Radhoštěm, Czech Republic :.. May 00, pp. -0, ISBN Analog Devices. : High Precision, Wideband RMS-to-DC Converter [online]. 00 [cit ]. Dostupný z WWW: < /ad/products/product.html>. Table. Effective values for triangular wave ETC M 00,0,0, 000,0,0, 00,0,0,0 000,0,0, Δ Δ δ δ 0,, 0, 0,,, 0, 0,,0 -,0 0, -0,, -, 0, -,0