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Three Phase Power / Energy IC with SPI Interface SA9904A
FEATURES + Bi-directional + + + +
active and reactive power/energy measurement RMS Voltage and frequency measurement Individual Phase information SPI communication bus Meets the IEC 521/1036 Specification requirements for Class 1 AC Watt hour meters
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Meets the IEC 1268 Specification requirements for VAR hour meters Protected against ESD Total power consumption rating below 60mW Uses current transformers for current sensing Operates over a wide temperature range Precision voltage reference on-chip
DESCRIPTION
The SAMES SA9904A is a three phase bi-directional energy/power metering integrated circuit that performs measurement of active and reactive power, mains voltage and mains frequency. The SA9904A is pin compatible to the SA9604A. New features include, RMS mains voltage and accurate reactive power measurements. Measured values for active and reactive energy, the mains voltage and frequency for each phase are accessible through a SPI bus from 24 bit registers. This innovative universal three phase power/energy metering integrated circuit is ideally suited for energy calculations in applications such as electricity dispensing systems (ED's), residential municipal metering and factory energy metering and control. The SA9904A integrated circuit is available in both 20 pin dualin-line plastic (DIP-20), as well as 20 pin small outline (SOIC20) package types.
VDD
VSS
IIP1 IIN2 IIP2 IIN2 IIP3 IIN3 IVP1 IVP2 IVP3
ACTIVE CURRENT ADC DI REACTIVE SPI RMS VOLTAGE VOLTAGE ADC MAINS FREQ. F150 DO SCK CS
GND
VOLTAGE REF.
OSC
Dr-01598
VREF
OSC1
OSC2
Figure 1: Block diagram
SPEC-0076 (REV. 5)
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SA9904A ELECTRICAL CHARACTERISTICS
(VDD = 2.5V, VSS = -2.5V, over the temperature range -10C to +70C#, unless otherwise specified.) Parameter Operating temp. Range Supply Voltage: Positive Supply Voltage: Negative Supply Current: Positive Supply Current: Negative Current Sensor Inputs (Differential) Input Current Range Voltage Sensor Input (Asymmetrical) Input Current Range Pins SCK High Voltage Low Voltage IIV VIH VIL fSCK tLO tHI Pins CS, DI High Voltage Low Voltage Pins F150, DO Low Voltage High Voltage Oscillator Pin VREF Ref. Current Ref. Voltage VIH VIL VOL VOH -25 VDD-1 VSS+1 800 0.6 0.6 VDD-1 VSS+1 VSS+1 VDD-1 +25 A V V kHz s s V V V V III -25 +25 A Symbol TO VDD VSS IDD ISS Min -25 2.25 -2.75 9.5 9.5 Typ Max +85 2.75 -2.25 11 11 Unit C V V mA mA
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Condition
Peak value
Peak value
IOL = 5mA IOH = -2mA
Recommended crystal: TV colour burst crystal f = 3.5795 MHz -IR VR 23 1.1 25 27 1.3 A V With R = 47kW connected to VSS Reference to VSS
ABSOLUTE MAXIMUM RATINGS*
Parameter Supply Voltage Current on any pin Storage Temperature Operating Temperature Symbol VDD -VSS IPIN TSTG TO Min -0.3 -150 -40 -40 Max 6.0 +150 +125 +85 Unit V mA C C
*Stresses above those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress rating only. Functional operation of the device at these or any other condition above those indicated in the operational sections of this specification, is not implied. Exposure to Absolute Maximum Ratings for extended periods may affect device reliability.
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SA9904A PIN DESCRIPTION
PIN 16 6 Designation GND VDD Description
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Analog Ground. The supply voltage to this pin should be mid-way between VDD and VSS. Positive Supply voltage. The voltage to this pin is typically +2.5V if a shunt resistor is used for current sensing or in the case of a current transformer a +5V supply can be applied. Negative Supply Voltage. The voltage to this pin is typically -2.5V if a shunt resistor is used for current sensing or in the case of a current transformer a 0V supply can be applied. Analog Input for Voltage Phase 1, Phase 2 and Phase 3. The current into the A/D converter should be set at 14ARMS at nominal mains voltage. The voltage sense input saturates at an input current of 25A peak.
14
VSS
17, 20, 3
IVP1, IVP2, IVP3
18, 19, 1, 2, 4, 5
IIP1, IIN1, IIP2, IIN2, Inputs for current sensors. The shunt resistor voltage from each channel is converted to a current of 16ARMS at rated conditions. The current sense input IIP3, IIN3 saturates at an input current of 25A peak. VREF OSC1, OSC2 SCK DO F150 DI CS This pin provides the connection for the reference current setting resistor. A 47kW resistor connected to sets the optimum operating condition. Connections for a crystal or ceramic resonator. (OSC1 = input; OSC2 = Output) Serial clock in. This pin is used to strobe data in and out of the SA9904A Serial data out. Data from the SA9904A is strobed out on this pin. DO is only driven when CS is active. Voltage zero crossover. The F150 output generates a 1ms pulse, on every rising edge of the mains voltage for each phase. Serial data in. Data is only accepted during an active chip select (CS). Chip select. The CS pin is active high.
15 10, 11 8 9 7 12 13
IIP2 IIN2 IVP3 IIP3 IIN3 VDD F150 SCK DO OSC1
1 2 3 4 5 6 7 8 9 10
DR-01599
20 19
IVP2 IIN1
ORDERING INFORMATION
Part Number SA9904APA SA9904ASA Package DIP-20 SOIC-20
18 IIP1 17 IVP1 16 GND 15 VREF 14 VSS 13 CS 12 DI
11 OSC2
Figure 2: Pin connections: Package: DIP-20, SOIC-20
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SA9904A FUNCTIONAL DESCRIPTION
The SA9904A is a CMOS mixed signal Analog/Digital integrated circuit, which performs the measurement of active power, reactive power, RMS voltage and mains frequency. The integrated circuit includes all the required functions for threephase power and energy measurement such as oversampling A/D converters for the voltage and current sense inputs, power calculation and energy integration. The SA9904A integrates instantaneous active and reactive power into 24 bit integrators. RMS voltage and frequency are continuously measured and stored in the respective registers. The mains voltage zero crossover is available on the F150 output. The SPI interface of the SA9904A has a tri-state output that allows connection of more than one metering device on a single SPI bus. R1 = R2 = (IL / 16ARMS) x RSH / 2 R3 = R4 = (IL / 16ARMS) x RSH / 2 R5 = R6 = (IL / 16ARMS) x RSH / 2 Where: IL = Line current/CT-ratio
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RSH = Shunt resistor or termination resistor (R25, R26, R27). In case a current transformer is used for current sensing the value of RSH should be less than the resistance of the CT's secondary winding. Voltage Sense Input (IVP1, IVP2, IVP3) The current into the voltage sense inputs (virtual ground) should be set to 14ARMS at rated voltage conditions. The individual mains voltages are divided down to 14VRMS per phase. The resistor R8, R9 and R10 set the current for the voltage sense inputs. The voltage sense inputs saturate at an input current of 25A peak.
INPUT SIGNALS
Analog Input Configuration The input circuitry of the current and voltage sensor inputs is illustrated in figure 3. These inputs are protected against electrostatic discharge through clamping diodes. The feedback loops from the outputs of the amplifiers AI and AV generate virtual shorts on the signal inputs. Exact duplications of the input currents are generated for the analog signal processing circuitry. The current and voltage sense inputs are identical. Both inputs are differential current driven up to 25A peak. One of the voltage sense amplifier input terminals is internally connected to GND. This is possible because the voltage sense input is much less sensitive to externally induced parasitic signals compared to the current sense inputs. Current Sense Inputs (IIN1, IIP1, IIN2, IIP2, IIN3, IIP3) At rated current the resistor values should be selected for input currents of 16ARMS. Referring to figure 8, the resistors R1 and R2 on current channel 1, resistors R3 and R4 on current channel 2 and resistors R5 and R6 on current channel 3, define the current level into the current sense inputs of the SA9904A. The current sense inputs saturates at an input current of 25A peak. Resistors R25, R26 and R27 are the current transformer termination resistors. The voltage drop across the termination resistors should be at least 16mV at rated conditions. Values for the current sense inputs are calculated as follows:
V DD
IIP
CURRENT SENSOR INPUTS
VSS VDD
AI
IIN
VSS VDD
IVP VOLTAGE SENSOR INPUT
V SS
AV
GND DR-01288
Figure 3: Analog input internal configuration
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SA9904A
Reference Voltage (VREF) The VREF pin is the reference for the bias resistor. With a bias resistor of 47kW optimum conditions are set. Serial Clock (SCK) The SCK pin is used to synchronize data interchange between the micro controller and the SA9904A. The clock signal on this pin is generated by the micro controller and determines the data transfer rate of the DO and DI pins. Serial Data In (DI) The DI pin is the serial data input pin for the SA9904A. Data will be input at a rate determined by the Serial Clock (SCK). Data will be accepted only during an active chip select (CS). Chip Select (CS) The CS input is used to address the SA9904A. An active high on this pin enables the SA9904A to initiate data exchange.
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OUTPUT SIGNALS
SERIAL DATA OUT (DO)
The DO pin is the serial data output pin for the SA9904A. The Serial Clock (SCK) determines the data output rate. Data is only transferred during on active chip select (CS). This output is tri-state when CS is low.
MAINS VOLTAGE SENSE ZERO CROSSOVER (F150)
The F150 output generates a signal, which follows the mains voltage zero crossings, see figure 4. The micro controller may use the F150 to extract mains timing.
ELECTROSTATIC DISCHARGE (ESD) PROTECTION
The SA9904A Integrated Circuit's inputs/outputs are protected against ESD.
POWER CONSUMPTION
The power consumption rating of the SA9904A integrated circuit is less than 60mW.
Phase 1
Phase 2
Phase 3
FM150
1mS
+5V
dr-01464
0V (Vss)
Figure 4: Mains voltage zero crossover pin FMO
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SA9904A SPI - INTERFACE
DESCRIPTION
A serial peripheral interface bus (SPI) is a synchronous bus used for data transfers between a micro controller and the SA9904A. The pins DO (Serial Data Out), DI (Serial Data In), CS (Chip Select), and SCK (Serial Clock) are used in the bus implementation. The SA9904A is the slave device with the micro controller being bus master. The CS input initiates and terminates data transfers. A SCK signal (generated by the micro controller) strobes data between the micro-controller and the SCK pin of the SA9904A device. The DI and DO pins are the serial data input and output pins for the SA9904A, respectively.
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The sequence 110 (0x06) must precede the 6-bit address of the register being accessed. When CS is HIGH, data on pin DI is clocked into the SA9904A on the rising edge of SCK. Figure 5 shows the data clocked into DI comprising of 1 1 0 A5 A4 A3 A2 A1 A0. Address locations A5 and A4 are included for compatibility with future developments. Registers may be read individually and in any order. After a register has been read, the contents of the next register value will be shifted out on the DO pin with every SCK clock cycle. Data output on DO will continue until CS is inactive. The 9 bits needed for register addressing can be padded with leading zeros when the micro-controller requires a 8 bit SPI word length. The following sequence is valid: 0000 0001 10A5A4 A3A2A1A0
REGISTER ACCESS
The SA9904A contains four 24 bit registers for each phase. The content represents active energy, reactive energy, mains voltage and mains frequency. The register addresses are shown in the following table: Header A5 A4 A3 A2 A1 A0 bits 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 X X X X X X X X X X X X X X X X X X X X X X X X 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1
ID 1 2 3 4 5 6 7 8 9
Register Active Phase 1 Reactive Phase 1 Voltage Phase 1
Frequency Phase 1 1 Active Phase 2 Reactive Phase 2 Voltage Phase 2 1 1 1
Frequency Phase 2 1 Active Phase 3 1 1 1
10 Reactive Phase 3 11 Voltage Phase 3
12 Frequency Phase 3 1
SCK
CS Read command DI DO 0 1 1 0 Register address A5 A4 A3 A2 A1 A0 Register Data D23 D22 D21 D1 D0 Next data register D23 D22 D1 D0 High impedance
Figure 5: SPI waveforms
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SA9904A
DATA FORMAT
Figure 5 shows the SPI waveforms. After the least significant digit of the address has been entered on the rising edge of SCK, the output DO goes low with the falling edge of SCK. Each subsequent falling edge transition on the SCK pin will validate the next data bit on the DO pin. The content of each register consists of 24 bits of data. The MSB is shifted out first.
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ACTIVE AND REACTIVE REGISTER VALUES
The active and reactive registers are 24 bit up/down counters, that increment or decrement at a rate of 320k samples per second at rated conditions. The register values will increment for positive energy flow and decrement for negative energy flow as indicated in figure 7. The active and reactive registers are not reset after access, so in order to determine the correct register value, the previous value read must be subtracted from the current reading. The data read from the registers represents the active or reactive power integrated over time. The increase or decrease between readings represent the measured energy consumption. Register wrap around
SCK t3 t4
Positive energy flow Register values
H7FFFFF ................ (8388607) H800000 (8388608) HFFFFFF ................ (16777215)
DI t2 t5
0
Negative energy flow
DO t1
DR-01590
Register wrap around Figure 7: Register increment / decrement showing the register wrap around
CS
DR-01545
Parameter Description t1 t3 t4 t2 SCK rising edge to DO valid SCK min high time SCK min low time Setup time for DI and CS
Min
Max
625ns 1.160s 625ns 625ns
At rated conditions, the active and reactive registers will wrap around every 26 seconds. The micro controller program needs to take this condition into account when calculating the difference between register values. As an example lets assume that with a constant load connected, the delta value (delta value = present register previous register value) is 22260. Because of the constant load, the delta value should always be 22260 every time the register is read and the previous value subtracted (assuming the same time period between reads). However this will not be true when a wrap around occurs, as the following example will demonstrate: Description Present register value Valiable Decimal Hex
before the rising edge of SCK 20ns t5 DI hold time 625ns
Figure 6: SPI Timing diagrams
new_val 16767215 0x00FFD8EF 16744955 0x00FF81FB 22260 0x000056F4
Previous register value old_val new_val - old_val = delta_val
The register now wraps around so after the next read the values are as follows: Present register value new_val 12259 0x00002FE4 16767215 0x00FFD8EF
Previous register value old_val new_val - old_val =
delta_val -16754955 0x00FFA90B
Computing this delta value will result in incorrect calculations.
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SA9904A USING THE REGISTER VALUES
ACTIVE AND REACTIVE ENERGY REGISTER
The active and reactive energy measured per count can be calculated by applying the following formulae: Energy per count = (VRATED x IRATED) / 320000 The active and reactive power measured by the SA9904A is calculated as follows: Power = (VRATED x IRATED x N / INTTIME / 320000 (In watt seconds or var seconds) Where: VRATED Rated mains voltage of meter IRATED Rated mains current of meter N Difference in register values between successive reads (delta value) INTTIME Time difference between successive register reads (in seconds)
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MAINS FREQUENCY REGISTER
Bits D0 to D9 represents a counter value that is scaleable to the mains frequency measured. The mains frequency measured by the SA9904A is calculated as follows: Frequency = FCRYSTAL / 256 / FREGISTER VALUE FCRYSTAL The external crystal frequency. FREGISTER VALUE Bits D9 to D0 of the frequency register. Bits D10 to D20 are not used in the frequency register. The phase error status may be ascertained from bits D21 and D22, as shown in the following table: Frequency data Bits D22 D21 0 1 X 0 0 1 Description No phase error Phase sequence error (2 phases swapped) Missing phase
MAINS VOLTAGE REGISTER
The RMS voltage measurement is accurate to 1% in a range of 50% to 115% of rated mains voltage. The RMS mains voltage measured by the SA9904A is calculated as follows: Voltage = VRATED x VREGISTER VALUE / 700 VRATED Rated mains voltage of meter VREGISTER VALUE Voltage register value
The phase error status is merged on all three frequency registers. Bit D23 is set with a rising edge of the mains voltage and cleared after 2ms.
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SA9904A TYPICAL APPLICATION
In figure 8, the components required for the three phase power/energy metering section of a meter, is shown. The application uses current transformers for current sensing. The 4-wire meter section is capable of measuring 3x230V/80A with precision better than Class 1. The most important external components for the SA9904A integrated circuit are the current sense resistors, the voltage sense resistors as well as the bias setting resistor.
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VOLTAGE DIVIDER
The voltage divider is calculated for a voltage drop of 14V. Equations for the voltage divider in figure 5 are: RA = R16 + R19 + R22 RB = R8 || R13) Combining the two equations gives: ( RA + RB ) / 230V = RB / 14V A 24k resistor is chosen for R13 and a 1M resistor is used for R8. Substituting the values result in: RB = 23.44k RA = RB x (230V / 14V - 1) RA = 361.6k. Resistor values of R16, R19 and R22 is chosen to be 120k each. The three voltage channels are identical so R14= R15= R16 = R17 = R18 = R19 and R20 = R21= R22.
BIAS RESISTOR
R7 defines all on-chip and reference currents. With R7=47kW, optimum conditions are set.
CT TERMINATION RESISTOR
The voltage drop across the CT termination resistor at rated current should be at least 16mV. The CT's used have low phase shift and a ratio of 1:2500.The CT is terminated with a 2.7W resistor giving a voltage drop across the termination resistor 86.4mV at rated conditions (Imax for the meter).
CURRENT SENSE RESISTORS
The resistors R1 and R2 define the current level into the current sense inputs of phase one of the device. The resistor values are selected for an input current of 16A on the current inputs at rated conditions. According to equation described in the Current Sense inputs section: = (IL / 16A ) x RSH / 2 = 80A /2500 / 16A x 2.7W / 2 = 2.7kW IL = Line current / CT Ratio The three current channels are identical so R1 = R2 = R3 = R4 = R5 = R6. R1 = R2
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SA9904A
Neutral R14 R12 R15 R11 R16 R19 R22 R18 R21 R17 R20
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CT1 19 IIN1 GND IVP1 R2 18 IIP1 IVP2 R3 2 IIN2 IVP3 3 R26 F150 SCK CS DI DO R4 1 IIP2 GND CT3 IIN3 VDD R6 4 GND R7 15 14 VSS VREF VSS DR-01600 OSC2 VDD 11 GND 6 VDD VSS R24 C1 C6 R23 IIP3 OSC1 10 X1 C2 R27 R5 5 F150 SCK CS DI DO 7 8 13 12 9 20 GND CT2 R9 R10 17 R8 GND 16 R25 R1 U1 R13 C5 C4 C3
GND
V3 In
V2 In
V1In
Figure 8: Typical application circuit
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V3 Out
V2 Out
V1 Out
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SA9904A
Parts List for Application Circuit: Figure 8
Symbol U1 R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15 R16 R17 R18 R19 R20 R21 R22 R23 R24 R25 R26 R27 C1 C2 C3 C4 C5 C6 CT1 CT2 CT3 Description SA9904A Resistor, 2.7k, 1/4W, 1% metal Resistor, 2.7k, 1/4W, 1% metal Resistor, 2.7k, 1/4W, 1% metal Resistor, 2.7k, 1/4W, 1% metal Resistor, 2.7k, 1/4W, 1% metal Resistor, 2.7k, 1/4W, 1% metal Resistor, 47k, 1/4W, 1%, metal Resistor, 1M, 1/4W, 1%, metal Resistor, 1M, 1/4W, 1%, metal Resistor, 1M, 1/4W, 1%, metal Resistor, 24k, 1/4W, 1%, metal Resistor, 24k, 1/4W, 1%, metal Resistor, 24k, 1/4W, 1%, metal Resistor, 120k, 1/4W, 1%, metal Resistor, 120k, 1/4W, 1%, metal Resistor, 120k, 1/4W, 1%, metal Resistor, 120k, 1/4W, 1%, metal Resistor, 120k, 1/4W, 1%, metal Resistor, 120k, 1/4W, 1%, metal Resistor, 120k, 1/4W, 1%, metal Resistor, 120k, 1/4W, 1%, metal Resistor, 120k, 1/4W, 1%, metal Resistor, 1k, 1/4W, 1%, metal Resistor, 1k, 1/4W, 1%, metal Resistor, 2.7R, 1/4W, 1%, metal Resistor, 2.7R, 1/4W, 1%, metal Resistor, 2.7R, 1/4W, 1%, metal Capacitor, 220nF Capacitor, 220nF Capacitor, 820nF Capacitor, 820nF Capacitor, 820nF Capacitor, 820nF Current Transformer, TZ76 Current Transformer, TZ76 Current Transformer, TZ76
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Detail DIP-20/SOIC-20 Note 1 Note 1 Note 1 Note 1 Note 1 Note 1
Note 1 Note 1 Note 1
Note 2 Note 2 Note 2 Note 3
Note 1: Resistor (R1 to R6) values are dependant on the selection of the termination resistors (R25 to R27) and CT combination. Note 2: Capacitor values may be selected to compensate for phase errors caused by the current transformers. Note 3: Capacitor C6 to be positioned as close as possible to supply pins VDD and VSS of U1 as possible.
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SA9904A PM9607AP
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DISCLAIMER:
The information contained in this document is confidential and proprietary to South African Micro-Electronic Systems (Pty) Ltd ("SAMES") and may not be copied or disclosed to a third party, in whole or in part, without the express written consent of SAMES. The information contained herein is current as of the date of publication; however, delivery of this document shall not under any circumstances create any implication that the information contained herein is correct as of any time subsequent to such date. SAMES does not undertake to inform any recipient of this document of any changes in the information contained herein, and SAMES expressly reserves the right to make changes in such information, without notification, even if such changes would render information contained herein inaccurate or incomplete. SAMES makes no representation or warranty that any circuit designed by reference to the information contained herein, will function without errors and as intended by the designer.
Any sales or technical questions may be posted to our e-mail address below: energy@sames.co.za
For the latest updates on datasheets, please visit our web site: http://www.sames.co.za. SOUTH AFRICAN MICRO-ELECTRONIC SYSTEMS (PTY) LTD Tel: (012) 333-6021 Tel: Int +27 12 333-6021 Fax: (012) 333-8071 Fax: Int +27 12 333-8071
P O BOX 15888 33 ELAND STREET LYNN EAST 0039 REPUBLIC OF SOUTH AFRICA
33 ELAND STREET KOEDOESPOORT INDUSTRIAL AREA PRETORIA REPUBLIC OF SOUTH AFRICA
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