MCU Competence Centre in Shanghai

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Electronic Energy Meter
2
Contents

• Background
• Classification
• Principle
• Block diagram
• Feature of the solution
• Hardware configure
• How to reuse the solution
• Other devices

3
Background

• Induction meter
• Lack of electric power
• Improve the management of electric power usage
• Electric technology development (A/D, MCU, DSP)

4
Classification

• According to measurement energy accuracy class
• 0.2s, 0.5, 0.5s, 1.0 and 2.0
• According to work principle of measurement unit
• Static (solid) type meter
• Induction (mechanical ) meter
• According to connection method
• Single phase meter
• 3 phase/3 wire meter
• 3 phase/4 wire meter
• According to function
• Pulse meter
• Multi-rate meter
• Prepayment meter
• Power line meter
• Multi-function meter

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Concepts of Electronics Metering

• Current and voltage of electricity are sampled in
  the same time.

• The immediate power consumption is calculated.
• Accumulated
• energy usage is displayed with step counter for
  user reference.

An example of measuring device
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Advantage of Electronics Metering

• Save natural material
• Higher reliability and accuracy
• Software automatic calibration available
• Prepayment available
• Multi-rate charging
• Remote meter reading
• Energy usage statistic
• Anti-tampering
• Multiple information display
• Same concept applies to gas and water metering.

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Features and General Block Diagram
P

• Features summary
• KWH measures
• LCD Display
• Storage Calibration Data

Low End
N
Power Supply

• Anti Tampering
• Maximum demand with date and time
• DateTime
• Cumulative Energy

Current sensor
Signal processing
Medium End
RAM
Voltage sensor
FLASH or ROM
ADC
Application Managememt

RTC Reset Circuit, Real Time Clock, Battery
EEPROM

• Automatic meter reading (IR, RF, IrDA, PLM)
• Multi Tariff (Peak hours, normal hours, etc)
• Meter calibration trough software
• Pre-paid module ( Card types used EEPROM card,
  Security card, Smart card)

LCD Driver
LED Driver
LCD Display
High End
AMR Communication Signal Processing
Smart Card Reader
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Benefit of ST solution

• Low risk
• Quality guaranteed
• Reduced time to market

Industrial proved solution

• Short learning curve
• Wide routines library available
• Existing know-how can be kept
• Wide selections of configuration

Blocked Architecture

• Pushs back the hardware limitations
• Possible evolution to higher speed
• Take full advantages of C language

Enhanced features
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Full set solution from ST
ICP
Sensor
LED
POWER SUPPLY
LCD DIPLAY
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Feature of the solution

• Precise measurement  
• Measure and record on active accumulative energy
• Measure individual active accumulative energy for
  positive and negative direction
• Measure individual active accumulative energy for
  different tariff rates (peak, day, low)
• Record and save all kind of the forward energy
  for 12 months
• Clock, interval time and tariff-rate
• Three tariff rate (Peak, Day, Low) and 12
  interval times
• Hardware clock device with high accurate date and
  time, and without leap year problem.
• Software compensation to ensure the higher
  accuracy.
• Accuracy is better than 0.5S/Day

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Feature of the solution

• Display to show user the different kinds of
  energy usage in LCD
• Software driver with I/O pins driving LCD panel
  directly
• There are 15 items to be displayed in turn. The
  display item can be hided or showed via
  communication programming. The display duration
  for every item can be set from 1s to 10s.
• There are two LEDs to indicate the different
  tariff rate.
• Communication to implement the Automatic Meter
  Reading (AMR) and remote configuration
• Compliant with the protocol of JiangSu Province
• Electronic-optical isolated RS485 interface
• Infrared interface
• PLM interface
• Capability of remote configuration with accessing
  date/time recorded
• Storage to save the energy usage in a
  non-volatile memory
• After power cut, all the data in Eeprom are valid
  over 10 years
• Write/read data with verification

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Advantages of solution

• Software LCD driver with I/Opins drive LCD
  directly.
• Internal A/D channel to monitorthe power failure
  and the batteryusage directly.
• The infrared carrier 38kHz isgenerated and
  modulated the data by MCU directly.
• With internal watch dog
• Adjusting the accuracy of clock via software
  method
• ESD protection in all Pins
• High sink pinsto drive LED directly
• IAP-- In-Application Programming, ICP-- In
  Circuit programming

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Hardware configuration

• SCI for RS485 communication
• 1 timer for Infrared communication
• 1 timer for PWM(38kHz)
• Basic time for LCD refresh
• 1 interrupt I/O pin for infrared communication
• 2 A/D channels for detecting power failure and
  battery usage
• High sink pinsto drive LED indicator directly

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How to use the solution

• The solution consists of 6 files main.c comm.c
  interface.c eeprom.c rtc.c init.c energy.c i2c.c.
• Modify the I/O pin function define.h and
  Initio()
• comm.c for adding or deleting the communication
  command
• Interface.c for driving the LCD and tariff rate
  indication
• Eeprom.c for how to organize the data to be
  read/written from/in eeprom
• Rtc.c for reading and writing real time clock
• Init.c for the initiallization
• Energy.c for energy pulse measure and energy
  calculation
• I2c.c to read and write data from/in eeprom
• Main.c for program loop
• With this detailed partition, user may focus on
  theparts that they want to add/modify and so on.

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Main devices in solution
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Other MCU

• STLite0X it is suitable for pulse power meter
• STLite2X suitable to implement power meter
  without display, for example shanghai protocol.
• ST72F324K suitable to implement
  multi-rate/prepay power meter with display, but
  It is no way to drive display panel, because of
  lack of I/O pins. It need other driver to drive
  LCD or Led display.
• ST72F324J suitable to implement
  multi-rate/prepay power meter with display, and
  it can drive LCD or LED directly.

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Other devices

• ST485EB
• LOW QUIESCENT CURRENT 300mA
• -7V TO 12V COMMON MODE INPUT VOLTAGE RANGE
• DRIVER MAINTAINS HIGH IMPEDANCE IN 3-STATE OR
  WITH THE POWER OFF
• 70mV TYPICAL INPUT HYSTERESIS
• 30ns PROPAGATION DELAYS, 5ns SKEW
• OPERATE FROM A SINGLE 5V SUPPLY
• CURRENT LIMITING AND THERMAL
• SHUTDOWN FOR DRIVER OVERLOAD PROTECTION
• ESD PROTECTION 15KV (H.B.M.) 8KV (IEC-1000-4-2
  CONTACT DISCHARGE)
• ALLOWS UP TO 256 TRANSCEIVERS ON THE BUS

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M41T81

• 2.0 TO 5.5V CLOCK OPERATING VOLTAGE
• COUNTERS FOR TENTHS/HUNDREDTHS OF SECONDS,
  SECONDS, MINUTES,HOURS, DAY, DATE, MONTH, YEAR,
  and CENTURY
• SERIAL INTERFACE SUPPORTS I2C BUS (400KHz
  PROTOCOL)
• WATCHDOG TIMER
• BATTERY BACK-UP
• OPERATING TEMPERATURE OF 40 TO 85C
• PACKAGE OPTIONS INCLUDE A 28-LEAD EMBEDDED
  CRYSTAL SOIC
• AUTOMATIC SWITCH-OVER and DESELECT CIRCUITRY
• PROGRAMMABLE ALARM and INTERRUPT FUNCTION (valid
  even during Battery Back-up Mode)
• LOW OPERATING CURRENT OF 400µA
• ULTRA-LOW BATTERY SUPPLY CURRENT OF 1uA

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ST7538

• ST7538 Main Features
• Receiver Sensitivity 1mVrms
• Maximum Input Signal 2.5Vrms
• Operating Current lt5mA
• PLI Current Capability up to 310mArms
• Programmable Features
• Carrier Frequencies 60kHz,66kHz,72kHz, 76kHz,
  82.05KHz, 86KHz, 110KHz, 132.5kHz
• Baud rate 600Bps, 1200Bps, 2400Bps, 4800Bps
• Serial Interface Mode Synchronous (SPI),
  Asynchronous, Packet
• Master Clock Output 4MHz, 8MHz, 16MHz
• Transmission Time-Out Disabled,1 or 3 s
• Transmission Synchro Disabled, Zero Crossing

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Cost Evaluation

• Chip set 35.0 (ST72F324, 24WC12, RS485, M41T81,
  ADE7755)
• Battery 15.0
• LCD panel 6.0
• Capacitor 10 x 0.01 1.0
• Resistance 100 x 0.02 2.0
• PCB 6.0
• Transformer 5.0
• Plastic box 12.0
• Others 10.0 (electrolytic capacitor, diode, and
  so on)

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Plan

• Make 10 sets demo board of multi-rate before
  week12
• Three phase multi functional power meter