Design Guide: TIDA-010037
High-Accuracy Split-Phase CT Electricity Meter Reference
Design Using Standalone ADCs
Description
This reference design implements Class 0.1 split-
phase energy measurement using high-performance,
multi-channel analog-to-digital converters (ADC). The
ADC samples current transformers (CT) at 8 kHz to
measure the current and voltage of each leg of the AC
mains. The reference design achieves high accuracy
across a wide input current range (0.05–100 A) and
supports high sampling frequencies necessary for
power quality features such as individual harmonic
analysis. An ADC sample rate of 32 ksps can be
acheived by disabling some software functions.
Independent ADCs provide flexibility in the choice of
metrology microcontrollers compared to integrated
SoCs. This reference design uses a SimpleLink
™
ARM
®
Cortex
®
-M4 host microcontroller for metrology.
The necessary software functionality is implemented
in the ADC Energy Metrology library. The software
library can be compiled with Code Composer Studio
™
or IAR Embedded Workbench
®
.
Resources
Design Folder
,
Product Folder
,
,
Product Folder
Product Folder
Software
Features
• Split-phase metrology for electricity meters that
meets ANSI C12.20 Class 0.1 active energy
accuracy requirements across 10000:1 input range
• Active and reactive energy and power, root mean
square (RMS) current and voltage, power factor,
and line-frequency calculations
• Isolated RS-232 and RS-485 with 5-kV
RMS
isolation
• Communications module expansion with current
limit and overvoltage and undervoltage protection
• Tested across 50 mA to 100 A input range
• High active energy accuracy still obtained when
ADC sample rate increased to 32 ksps
• Software for energy metrology and displaying
results on a Windows
®
PC GUI.
Applications
•
•
•
6'
ADC
6'
ADC
-
Source From Utility
Load
Phase A
Phase A
N
e
u
tra
l
+
+
-
ADS131M04
N
e
u
tra
l
SCLK
DIN
DOUT
DRDY
VCC
GND
6'
ADC
6'
ADC
-
+
+
-
SPI MISO
GPIO
Interruptible GPIO
SPI CLK
SPI MOSI
CLKIN
VDD
GND
SMCLK
RESET VCC
CSn
Phase B
Phase B
I
A
I
B
CT
CT
+
-
TOTAL
A
B
kWh
VCC
GND
Lx
MSP432P4111
GPIO
GPIO
VCC
GND
ISO-DVCC
ISO-GND
ISO-ACTIVE
ISO-REACTIVE
ISO7720
DVCC
DVSS
Active
Reactive
TPS3840
VCC
RESET
CT
GND
RST/NMI
TPS709
GND
VCC
GND
5V_IN
TVS1800
TPS25921L
5V_LMT
Lx/PMAP GPIO
UART2 TX
UART2 RX
RS-232
Connection
ISO7731 B
VCC
GND
TPS709
TRS3232E
DTR
RTS
RGND
RS232_VCC
RS232_GND
Board
Header to
External
Radio/Radio
Module
5V_LMT
GND
Lx/PMAP GPIO
Lx/PMAP GPIO
Lx/PMAP GPIO
THVD1500
RS-485
Connection
GPIO
RE
WE
RGND
VCC3
V
B
V
A
Description
TIDUEM8B – MARCH 2019 – REVISED FEBRUARY 2021
High-Accuracy Split-Phase CT Electricity Meter Reference Design Using
Standalone ADCs
1
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