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부품번호 | ATT7030A 기능 |
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기능 | Application Note | ||
제조업체 | hitrendtech | ||
로고 | |||
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ATT7030A Application Note(260-CS-105)
ATT7030A
Application Note
http://www.hitrendtech.com
版权归钜泉光电科技(上海)有限公司所有
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ATT7030A Application Note(260-CS-105)
ATT7030A’s package is QFP44. The external hardware circuitry includes power supply, voltage
and current analog signal input, pulse output and electromechanical counter.
Analog input circuitry
ATT7030A incorporates 6 second-order 16-bits ADCs. The voltage sampling data is 0.2V ~ 0.6V.
The current sampling data is 2mV ~ 1V. The energy linear error is less than 0.1%.
Every ADC’s AC signal is input from VxP and VxN. At the same time the VxP and VxN need be
added 2.4V direct current bias voltage, which could be obtained from ATT7030A’s reference voltage
output ‘REFOUT’ or external benchmark voltage.
ATT7030A’s sampling input voltage can adopt resistance divided-voltage method (as diagram 1
and diagram 2), or switching voltage to current, then through current mutual inductance implement
switching current to voltage (as diagram 3). The latter method adopt mutual inductance implement,
which can segregate chip and electric power net, thereby can get favorable anti-jamming capability. In
diagram 1, the neutral line Vn is connected to reference voltage output ‘REFO’, which achieves adding
AC sampling signal to 2.4V direct current bias voltage expediently. In diagram 2, the neutral line Vn is
connected to chip’s ground, which is applied to power supply using autotransformer.
Diagram 1: Vn is connected to REFO
Diagram 2: Vn is connected to ground
Diagram 3: current mutual inductance
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ATT7030A Application Note(260-CS-105)
Follow above two formula, Hfreq=5760000000* Vu*Vi*G*G/(N*Un*Ib) (3)
By usually, Vi is 0.1V; Vu (0.2V ~ 0.6V) is selected to make Hfreq close to the value in List-1
basing on Un, Ib and pulse constant N.
List-1
SCF
S1
S0
Hfreq
Lfreq
0 0 0 256 16
0 0 1 128 16
0 1 0 128 8
0 1 1 128 4
1 0 0 64 16
1 0 1 64 8
1 1 0 64 4
Lfreq is divided-frequency coefficient for driving electromechanical counter. The ratio
of electromechanical counter should be:
N/Lfreq*2
(4)
Give a example: design a 3 phase 4 wire meter, the rated voltage is 220V, rated
current is 5A, then how to select pulse const? How to select ratio of electromechanical
counter? How to select SCF/S1/S0? How much is the sampling voltage in voltage loop?
Step 1: suppose Vu = 0.5V, Vi = 0.1V, by formula 3:
Hfreq=5760000000*0.5*0.1*0.648*0.648/(220*5*N)
=109938/N
Then N=109938/ Hfreq
Hfreq
256
128
64
N 429 858 1717
So pulse constant can be selected as 429 ~ 1717. Calibration pulse would be faster
along with pulse constant’s augment, which can shorten calibration time in feeble-signal.
Pulse constant can be selected as 400, 800, or 1600 after switched to integer;
corresponding Hfreq is 256, 128, 64.
If pulse constant is selected as 320, then sampling voltage = 0.5*320/429 = 0.37V, at
this time corresponding Hfreq is still 256.
Step 2: select ratio of electromechanical counter
Basing on List-1, if Hfreq = 256, then Lfreq = 16, so ratio = 400/16*2=50, SCF/S1/S0 = 0/0/0. If
pulse const is 320, then ratio is 40.
If Hfreq = 128, Lfreq can be selected as 16, 8, or 4. When Lfreq = 16, ratio = 800/16*2=100,
SCF/S1/S0 = 0/0/1. When Lfreq = 8, ratio = 800/8*2=200, SCF/S1/S0 = 0/1/0. When Lfreq = 4, ratio =
800/4*2=400, SCF/S1/S0 = 0/1/1.
If Hfreq = 64, Lfreq can be selected as 16, 8, or 4. When Lfreq = 16, ratio = 1600/16*2=200,
SCF/S1/S0 = 1/0/0. When Lfreq = 8, ratio = 1600/8*2=400, SCF/S1/S0 = 1/0/1. When Lfreq = 4, ratio =
1600/4*2=800, SCF/S1/S0 = 1/1/0.
Step 3: calculate sampling voltage Vu
By usually, CT achieves ATT7030A’s sampling input current. Connect appropriate resistance at
CT’s secondary coil can make Vi = 0.1V. By formula (3):
Vu = Hfreq*N*Un*Ib/(5760000000*Vi*G*G)
= 64*1600*220*5/(5760000000*0.1*0.648*0.648)
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