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1、always adopts mechanical tinplate to measure. There are some shortcomings that the measurement precision falls with machine abrasion, single time period setting and strong manpower 2. In this paper, we propose a novel multi-rate three-phase watt-hour meter based on AT89LV52. This multi-rate three-ph
2、ase watt-hour meter adopts AD7752 for measurement. It has the characteristics which are time-sharing measurement, accurate measurement, LCD display, automatic meter reading, flexible time period setting, timely emendation, low cost and novel design.II. STRUCTURE AND WORKING PRINCIPLEThe novel multi-
3、rate three-phase watt-hour 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 s
4、ix 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 diagramThe principle of this multi-rate watt-hour meter is reading in themulti-rate time segments
5、using RS485 bus and noting in X25045 then take over correctional clock with RS485 bus and write in clock CMOS chip S3530A. The three-phase 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
6、 complete 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 memorizeraccording to corresponding pe
7、riod of time. We write it to corresponding address of X25045 when the electrical energy achieves one degree in order to make the multi-rate measurement come true. This watt-hour meter hasfunctions of clear LCD display, missing phase detection, burthen control, halt electricity check and storage, aut
8、omatic meter reading and so on.III. THE DESIGH OF HARDWARE CIRCUITA Electrical energy measurementThe three-phase electrical energy measurement is realized by the low consume CMOS chip AD7752 of ADI company. The inside of AD7752 adopts digital circuit besides ADC, filter and multiplication circuit wh
9、ich can eliminate noises effectively. The sampling course of voltage and electric current in three-phase 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 tran
10、sformed to electrical pulse for output. The pulse of fan-out CF enters intointerregnum INT0 of AT89LV52 through photoelectricity insulation 4N25. CPU measures the electrical energy 4. We adjust the pulse number of CF by combining the state of S1 and S2. The connection of electrical energy and pulse
11、is W = M C . In which, W is the electrical energy with the unit of kilowatt-hour, M is the total pulse number, C is the pulse number of ammeter. We choose C equals to 3000 that is to say every kilowatt-hour is 3000pulses.Figure 2. Circuit schematic diagramof watt-hour meterB LCD displayThe LCD displ
12、ay 6 adopts HT1621 CMOS chip of HOLTEK Company toachieve twelve bits digital display. HT1621 is the LCD drivers with 128 segments (32 4) inner memorizer. The interior of HT1621 consists ofcontrol and time circuits, RAM, LCD drive and watch timer. It hasthe merits of small volume and low cost so that
13、 it is suit to watt-hour 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 c
14、hip has 48 nodes in which COM0, COM1, COM2, COM3 connect to the communal 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 20k is put between VDD and VLCD to adjust the display contrast of LCD. Experimen
15、t shows that the contrast is better with VDD=5V and VLCD=4V.C Serial memorizerSerial memorizer adopts low power consumption chip X25045 of XICORcompany .It has three functions which are watchdog timer WTD, voltage supervision and serial memorizer E2PROM with 512 bytes. WTD can be set 200ms, 600ms an
16、d 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 watt-hour meter reset in order to prevent program flying away. As the serial memorizer chip, 512 bytes of X25045 are used to storage the watt-
