【文章內(nèi)容簡(jiǎn)介】 tirate threephase watthour meter based on AT89LV52. This multirate threephase watthour meter adopts AD7752 for measurement. It has the characteristics which are timesharing measurement, accurate measurement, LCD display, automatic meter reading, flexible time period setting, timely emendation, low cost and novel design. II. STRUCTURE AND WORKING PRINCIPLE The novel multirate threephase watthour meter proposed in this paper is based upon AT89LV52 singlechip [3]. AT89LV52 has the flash memorizer with 8k bytes, cryptographical program memorizer with third class, RAM with 256 bytes, 32 programmable I/O lines, three time/ counter with 16 bits and a two class halt with six vectors. The interface circuit adopts I2C bus unit which is a 8 bits singlechip with good performance and suitable price. The system structure diagram is shown in figure 1. Figure 1. System structure diagram The principle of this multirate watthour meter is reading in the multirate time segments using RS485 bus and noting in X25045 then take over correctional clock with RS485 bus and write in clock CMOS chip S3530A. The threephase AC voltage and electric current pass through potentiometer and mutual inductance instrument respectively so as to produce small signal which is sent to AD7752 to plete measurement. The clock CMOS chip S3530A gives clock information per second in the course of automatic move and analyze this clock belongs to which period of time according to advance periods of time set in X25045 then save the electrical energy in RAM memorizer according to corresponding period of time. We write it to corresponding address of X25045 when the electrical energy achieves one degree in order to make the multirate measurement e true. This watthour meter has 本科學(xué)生畢業(yè)設(shè)計(jì) （論文）附件 附件 C：譯文 C11 functions of clear LCD display, missing phase detection, burthen control, halt electricity check and storage, automatic meter reading and so on. III. THE DESIGH OF HARDWARE CIRCUIT A． Electrical energy measurement The threephase electrical energy measurement is realized by the low consume CMOS chip AD7752 of ADI pany. The inside of AD7752 adopts digital circuit besides ADC, filter and multiplication circuit which can eliminate noises effectively. The sampling course of voltage and electric current in threephase AC power supply loop is shown in figure 2 in which IA stands for voltage sampling of A phase. The sampling circuits of B phase and C phase are similar to A phase. The power after integral is transformed to electrical pulse for output. The pulse of fanout CF enters into interregnum INT0 of AT89LV52 through photoelectricity insulation 4N25. CPU measures the electrical energy [4]. We adjust the pulse number of CF by bining the state of S1 and S2. The connection of electrical energy and pulse is W = M C . In which, W is the electrical energy with the unit of kilowatthour, M is the total pulse number, C is the pulse number of ammeter. We choose C equals to 3000 that is to say every kilowatthour is 3000 pulses. Figure 2. Circuit schematic diagramof watthour meter B． LCD display The LCD display [6] adopts HT1621 CMOS chip of HOLTEK Company to achieve twelve bits digital display. HT1621 is the LCD drivers with 128 segments (32 4) inner memorizer. The interior of HT1621 consists of 本科學(xué)生畢業(yè)設(shè)計(jì) （論文）附件 附件 C：譯文 C12 control and time circuits, RAM, LCD drive and watch timer. It has the merits of small volume and low cost so that it is suit to watthour meter. We use serial interface which only has four lines between HT1621 and AT89LV52. The detailed connection is shown in figure 3. P20, P21, P22 and P23 of AT89LV52 connect to CS, RD, WR and DATA respectively with the use to refurbish the display of RAM. HT1621 drive CMOS chip has 48 nodes in which COM0, COM1, COM2, COM3 connect to the munal end and drive output of LCD and SG0, SG1, SG2, SG3 connect to drive output of every segment respectively. In addition, an adjustable resistance of 20kΩ is put between VDD and VLCD to adjust the display contrast of LCD. Experiment shows that the contrast is better with VDD=5V and VLCD=4V. C． Serial memorizer Serial memorizer adopts low power consumption chip X25045 of XICOR pany .It has three functions which are watchdog timer WTD, voltage supervision and serial memorizer E2PROM with 512 bytes. WTD can be set 200ms, 600ms and 1400ms time intervals. The software program is read into X25045. During the normal running of program, WTD receives the trigger signal in time intervals in order to ensure the normal running of program. X25045 will output a high potential through RESET line if WTD does not receive trigger signal in time intervals. The trigger watthour meter reset in order to prevent p