RX210 Single-phase Two-wire Electricity Power Meter
Contents
1. No B Figure 8 Key Press processing Flow Chart R01AN1212EU0101 Rev 1 01 Dec 03 2012 Connect to the ege connerie Host If user Yes Enable data select Send i send T Be Yes Stop all sending Be If user A gt and disconnect sog taput Stop from host No Figure 9 Communication Software Flow Chart 2tENESAS Page 15 of 18 RX210 Single phase Two wire Electricity Power Meter 0 Capture both voltage and current sample Perform Averaging on both voltage and current data a SE Set Data Valid Flag Y EN Is 64 Sample capture done Figure 10 Front end signal Processing Flow chart Yes Perform RMS power and PF calculations Is Valid Data available R01AN1212EU0101 Rev 1 01 Dec 03 2012 Figure 11 Calculation Software Flow Chart Page 16 of 18 v ENE SAS RX210 Single phase Two wire Electricity Power Meter 5 References 1 Renesas Electronics RX210 Group User s Manual Hardware 2 Renesas Electronics RO1DS0041EJ0090 RX210 Group Preliminary Data sheet 3 Collins A Solid state solutions for electricity metrology Metering and Tariffs for Energy Supply Ninth International Conference on Conf Publ No 462 Aug 1999 4 Walt Kester Understand SINAD ENOB SNR THD THD N and SFDR so You Don t Get Lost i2. extra electromagnetic noise is induced in the vicinity of LSI an associated shoot through current flows internally and malfunctions occur due to the false recognition of the pin state as an input signal become possible Unused pins should be handled as described under Handling of Unused Pins in the manual 2 Processing at Power on The state of the product is undefined at the moment when power is supplied The states of internal circuits in the LSI are indeterminate and the states of register settings and pins are undefined at the moment when power is supplied In a finished product where the reset signal is applied to the external reset pin the states of pins are not guaranteed from the moment when power is supplied until the reset process is completed In a similar way the states of pins in a product that is reset by an on chip power on reset function are not guaranteed from the moment when power is supplied until the power reaches the level at which resetting has been specified 3 Prohibition of Access to Reserved Addresses Access to reserved addresses is prohibited The reserved addresses are provided for the possible future expansion of functions Do not access these addresses the correct operation of LSI is not guaranteed if they are accessed 4 Clock Signals After applying a reset only release the reset line after the operating clock signal has become stable When switching the clock signal during program execution wait u
3. absolute accuracy should be considered when judging the ADC accuracy For example a 12 Bit resolution ADC may have an absolute accuracy of 8 bits only due to a total error of 4 bits From the example calculation above we found out that we need an ENOB of 14 bits so the 12 Bit resolution ADC with 8 bit absolute accuracy will not work unless some tricks can be used to increase the accuracy Luckily there are some ways to improve accuracy through software processing The target of this application note is not to address accuracy requirements instead it focuses on how the RX210 can support a smart electricity meter application from the hardware perspective Single phase Two wire Electricity Power Meter Power Line Interfacing The meter need to measure AC voltage and AC current and depending on the number of phases and configuration it requires from two to eight ADC inputs The example in Figure 1 shows a single phase 2 wire topology Both voltage and current signals need to be measured at the same instance The line voltage is scaled down using resistor divider to get a signal within the ADC input range A current transformers CT is used to convert the load current to a lower value and shunt resistors are provided to convert to voltage signal proportional to load current Smart electricity meter applications require accurate input signal measurement and data processing hence all high accuracy resistors used in the front end If the current signal
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6. engine can furthermore reduce the total system cost Targeting smart meter applications with high levels of integration this application note will explore the capabilities of the Renesas RX210 Group Smart electricity meters are becoming the standard in many developed countries around the world due to the new demands in accurate energy consumption monitoring reporting and billing Depending on the measurement accuracy requirements the type of information as well as the way the utility companies get this information from the meter various complexities levels can be expected Higher accuracy meters use high resolution ADCs or dedicated metrology chips and have extended capabilities in filtering and energy computation Automatic Meter Reading AMR requirements are also differentiating factors and can add levels of complexity that can only be addressed with higher performance devices Advanced smart meters can cover these high demands by using multiple microcontrollers MCU or digital signal processors DSP RO1AN1212EU0101 Rev 1 01 Page 1 of 18 Dec 03 2012 RENESAS RX210 Single phase Two wire Electricity Power Meter Contents 1 Energy Meter Requirements A 3 2 AX200 Series Descriptor seines esiaine aaea aaa a aa E aaa ence edEESddEEERgegde gene 6 3 Hardware Reference Design using RX210 nnt 8 d Software Reference Design wisi cececeisiecdencaieieesvaidescncetvactehaeredentaavinevvis lees K aAA UEEN Edge Eege 12 e DEE 17 Figures Figur
7. main program loop to initialize the interface devices and displays values in regular interval Calling ADC driver subroutines for analog front end device to capture voltage and current values Calling LCD Display driver subroutines to display values Calling data archival module routines to save or retrieve configuration calibration and measured data Calling other miscellaneous subroutines for basic Smart Electricity Meter application Some of the high level software flow charts are presented in Figure 7 Figure 8 Figure 9 Figure 10 and Figure 11 RO1AN1212EU0101 Rev 1 01 Page 13 of 18 Dec 03 2012 RENESAS RX210 Single phase Two wire Electricity Power Meter Initialize storage pointer to begining Initialize storage pointer Initialize timer Interrupt Check For input AC voltage Display Start Message No Input Display Error Message Figure 7 Meter Initialization flow chart RO1AN1212EU0101 Rev 1 01 Page 14 of 18 Dec 03 2012 2tENESAS RX210 Single phase Two wire Electricity Power Meter d Tf user Yes Display RMS Nnput Sjenut voltage voltage No If user Display RMS ut curre current ee Yes Display If user put Powe Average Power e Display t Power Reactive eue Power Display Apparent Power f user es Yes Display Powerfactor nput Power
8. with two of the 12 Bit ADC inputs A segment LCD module is typically used to display voltage current instant power accumulated energy power factor etc Meter reading is supported through a simple optical pulse port or trough more complex IO extension cards for wireless or power line communication technologies Other I O functions include push buttons and LEDs for diagnostic and manual controls External flash memory and EEPROM are used for firmware upgrades and data storage gt LCD Display A L1 V Amplifier an Filter oy KEYPAD J ake a L1 1 Amplifier Filter j USB ADC Bluetooth J Reference Amp ifier 12 Bit Filter J 3 3V Temperature Amp ifier S Sensor Filter E ieee Microcontroller lt EEPROM N 120 240 VAC Power Management Figure 1 Block Diagram Energy Meter Analog Front End One of the most important parts of an electricity meter is the analog front end AFE Depending on the accuracy requirements the AFE can be a high resolution ADC or dedicated metrology chips The AFE has to also provide filtering and signal conditioning The design example described in this application note is targeted towards the lower accuracy grades of the 0 5 to 1 classes as specified in the ANSIC12 20 According to the standard for a typical 100A meter the accuracy range is between 1A and 100A In other words the utilities are i
9. 4 bits can be achieved This solution enables to get a maximum of 16 bits and closer to achieve the required ENOB to get the accuracy and dynamic range required for the energy meter This enables the meter to capture energy up to 10 harmonic The system consisting of front end PGA low pass filter before ADC and oversampled ADC with decimation filter as a whole has the better than required dynamic range of 1 100 In addition the noise is minimized using a 256 tap FIR low pass decimation filter with cutoff at 500 Hz The only limitation of this design is that it cannot measure energy up to the 19 harmonic but can measure up to 10 harmonic of 50 Hz AC signal Voltage reference The RX210 does have an internal reference voltage for the ADC but it is only used for calibration An external reference is provided using a shunt regulator TL431 for ADC operation The shunt regulator is used to generate a reference voltage of 2 5V first then 1 25V This allows the ADC to measure a signal up to 1V peak to peak LCD Display RX210 does not have on chip LCD driver or controller The design uses uPD71312 LCD driver to provide an interface to LCD display RX210 communicates with LCD driver using DC bus PD71312 requires 400 KHz clock which is generated by RX210 timer LCD reset functionality is provided by using a GPIO pin A single line LCD display is connected to the LCD driver for displaying the calculated values Keypad The key pad is actually consists
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11. Page 9 of 18 Dec 03 2012 RENESAS RX210 Single phase Two wire Electricity Power Meter from the manufacturer data sheet of the transformer By using oversampling and averaging ADC resolution is further increased and noise is reduced The following estimates the time required for capturing one set of voltage and current values for the RX210 based meter Total time ten 1 el be n conv x n enn For single phase meter tsu Channel dedicated sample and hold circuits sampling time 30 ADCLK cycles Dos Disconnection detection assist processing time 0 tcony A D conversion processing time 50 ADCLK cycles tsuep Channel dedicated sample and hold circuit sampling and holding end time 2 ADCLK cycles n Voltage and Current 2 Total Time 30 100 2 132 ADCLK 2 64 uS ADCLK 50 MHz This works out that effective sample rate is 378 KSPS Above calculation is for the continuous scan and does not include initial time and diagnostic and temperature scans Practically 256 KSPS is achievable with diagnostic and temperature scans included In order to measure up to 19 harmonic a Nyquist frequency of 2 KHz is required for 50 Hz AC signal If the specification is modified to limit the bandwidth of the signal to 500 Hz Nyquist frequency can be reduced to 1 KHZ The sample rate for x256 oversampling is 256 KSPS which gives a time 3 9 uS for getting one sample With a factor of 256 for oversampling and averaging an improvement of
12. ate an interrupt when pressed The status is captured by the keypad driver after required debouncing and is preserved till action is performed on the key press The driver provides all the routines necessary for the above functionality LED Driver This driver provides hardware abstraction layer for controlling on board LEDs through GPIO lines Flash Driver RX210 has on board data flash which can be used as non volatile medium to store configuration calibration data In addition it can be used to archive data for presenting trending This driver provides all the initialization configuration read write erase routines to use the data flash RO1AN1212EU0101 Rev 1 01 Page 12 of 18 Dec 03 2012 RENESAS RX210 Single phase Two wire Electricity Power Meter SPI Driver RX210 provides high speed SPI ports for serial communication These ports are used to support wireless or RS232 RS485 communication capability for the meter by using external hardware The SPI driver provides all the routines required to configure the data transfer Send and Receive data using the port The middleware like wireless stack communicate with the external hardware using this hardware abstraction layer Middleware These are software modules which provide much of the processing and number crunching in the energy meter application Signal Acquisition The signal acquisition module captures digitized values of voltage and current in to memory buffer and performs n
13. e Anomaly detection support for system clock failure flash memory integrity and ADC self check A block diagram of RX210 is presented in Figure 3 RO1AN1212EU0101 Rev 1 01 Page 6 of 18 Dec 03 2012 RENESAS RX210 Single phase Two wire Electricity Power Meter E2 data flash WDT JUUUU i ELC CRC SClc x 6 channels SCld x 1 channel RSPI x 1 channel RIIC x 1 channel MTU2 x 6 channels TMR x 2 channels unit 0 TMR x 2 channels unit 1 CMT x 2 channels unit 0 o S g E g 2 g E i S _ CMT x 2 channels unit 1 ICU KO RTC a 2 bit A D converter x 16 channels Port 2 Temperature sensor 10 bit D A converter x 2 channels 3 ZE Je is C Port A 5 Port B e z Es D i 3 B ia ES ICU Interrupt control unit RSPI Serial peripheral interface DTC Data transfer controller RIIC C bus interface DMACA DMA controller MTU2 Multi function timer pulse unit 2 BSC Bus controller POE2 Port output enable 2 WDT Watchdog timer TMR 8 bit timer IWDT Independent watchdog timer CMT Compare match timer ELC Event link controller RTC Realtime clock CRC CRC cyclic redundancy check calculator DOC Data operation circuit SCI Serial communications interface CAC Clock frequency accuracy measuring circuit Figure 3 Block Diagram of RX210 RO1AN1212EU0101 Rev 1 01 Page 7 of 18 Dec 03 2012 RENESAS RX210 Single phase Two wire Electricity Power Met
14. e I Block Diagram Energy Meter siii cccisccsctcscescscssthseceetis cansacaocsdbedes cones sbeveccnbisclivaveschascvenctocestevedevssscessuensideebeosbavsees 3 Figure 2 Signal Flow Diagram of Energy Meter 4 Figure 3 Block Diagram Of RXS2I0 E 7 Figure 4 Reference Design of Energy Meter using RX210 oo cee eeeeesseseesecsseesecseesecseeeecsaececeecsaeceaeseeecsaeeeesaesaeeaeeneeaees 8 Figure 5 Analog Front End for RX210 based Energy Meter 9 Figure 6 Software Architecture of Energy Meter cceeccssscsecssessceecsseeseesecaeesccseeseesecsaecnecaeesecneseeesaeeeesaeaeeeeeeessrenaees 12 Figure 7 Meter Initialization flow chat 14 Figure 8 Key Press processing Flow Chat t sssscsssesssseesoeconesetsevenesonencesesonencscsessenerenensesesensnsssesessnssesorsesenereesaneneres 15 Figure 9 Communication Software Flow Chart 15 Figure 10 Front end signal Processing Flow chat 16 Figure 11 Calculation Software Flow Chat 16 Tables Table 1 Requirements mapping for Energy Meter 8 RO1AN1212EU0101 Rev 1 01 Page 2 of 18 Dec 03 2012 RENESAS RX210 Single phase Two wire Electricity Power Meter 1 Energy Meter Requirements Block Diagram A typical smart meter system block diagram is shown in Figure 1 This design is based on the wideband sampling technique and uses a single 12 bit SAR ADC to sample voltage and current signal values The example shows a single phase two wire design where one line voltage and one phase current are measured
15. e energy meter is shown in Figure 6 The architecture is well suited to be implemented on RX210 microcontroller The signal acquisition module depends on the type of the front end hardware l Calculation Engine g a a Y Wireless 5 Stack C Signal N Timer gt Data L Acquisition J Module Archiving J Bee N LCD KeyPad ADC a LED Flash SPI N Driver 8 Driver Driver Q Driver Driver Driver d Hardware Abstraction D Figure 6 Software Architecture of Energy Meter Low Level driver routines These are the routines which provide hardware abstraction layer for the meter hardware ADC Driver The ADC driver allows the full control of the analog front end configuration including sample and hold circuits ADC channel scanning and transferring ADC data to memory buffer This also allows configuration for different scan rates for internal temperature sensor and voltage internal voltage reference LCD Display Driver In the display driver data to be displayed is transferred to LCD data buffer then LCD functions will handle display data and map onto appropriate LCD segment This process includes from top to bottom level functions such as LCD_string LCD_putc and LCD_MultSegWrite and so on The rest of lower level functions are DC communication interface functions to LCD driver device uPD71312 Keypad Driver The key switches are configured to gener
16. e requirements of data archival functionality Power Supply The power supply needs to provide necessary power for the microcontroller and analog front end hardware Most of the microcontrollers use 3 3V and the analog front end may use 3 3V or 5 V The power supply needs to take 120 240 VAC and generate these voltages with good regulation and low ripple In addition the power supply need to provide good isolation to protect the equipment connected to the meter using RS232 RO1AN1212EU0101 Rev 1 01 Page 5 of 18 Dec 03 2012 RENESAS RX210 Single phase Two wire Electricity Power Meter 2 RX200 Series Description The RX210 has up to 16 channels of 12 bit successive approximation type ADC suitable to monitor external analog inputs internal temperature sensor output and internal reference voltages Three of the channels have dedicated sample amp hold circuits with a fast conversion time of lus With a performance of 78 DMIPS 50MHz operation supported by 32 Bit X 32 Bit single cycle MAC engine the RX210 is a very good fit to address not only the sensing needs of most electricity meters but also the computation intensive metrology requirements Renesas unique low power zero wait state MONOS Flash technology allows RX210 MCU to fetch instructions without delay and with minimum power consumption Competing technology utilizes a high voltage transistor for readout and hardware accelerators to compensate for a slower Memory Flash resulting i
17. ecessary processing before passing the data to calculation engine To improve ENOB signal is oversampled and averaging is performed on the captured data in the module Further simple filtering is done to remove DC value in the input signal Calculation Engine The calculation engine which is the heart of the energy meter performs RMS calculation instantaneous power calculations and accumulated power and energy calculations This module may use floating point as well as signal processing algorithms to achieve necessary results Timer Module This module generates accurate pulses whose repetitive rate is proportional to the load energy being measured and takes the input from the calculation engine It uses the LED driver to control on board LEDs to generate optical pulse Data Archiving Energy consumption varies depending on the time of the day and time of the year If the energy data measured is saved periodically and can be retrieved later for analysis energy conservation programs can be devised The data archiving module provides these functionality by saving data to on board data flash It also provides routines to access the archived data Main application program The main application program uses all the drivers and middleware to provide basic Smart Energy Meter functionality Some of the software included in the application is Meter initialization code including system initialization called before the main program starts The
18. er 3 Hardware Reference Design using RX210 A reference design of Energy meter using RX210 is shown in Figure 4 and requirement mapping is presented in Table 1 As it can be seen majority of the functionality required is built in to RX210 microcontroller Isolated Power Supply 32KHz Segment LCD 3 3V ne uPD71312 V1 Filter RX210 EE Los R5F52108ADFP Optical Port 512KB Flash S S 11 Amplifier 64KB RAM lt e Filter AMR RS 232 A0 A23 VO DO D15 Extension Bus cont Firmware Data and Event log program Load profile Parameters Figure 4 Reference Design of Energy Meter using RX210 Table 1 Requirements mapping for Energy Meter Key Requirements RX210 External LCD Display DC LCD Driver uPD71312 Keypad GPIO USB Connectivity SPI Zig Ree ADC 8 channel 12 bit SAR with 3 channel Sample and Hold Voltage Reference Internal Voltage Reference for External required for accuracy diagnostics Non volatile storage 8 KB Data Flash Smaller EEPROM using I2C Signal Processing Hardware MAC helps in implementing signal processing algorithms Power Supply 3 3V 24V 5V Various hardware blocks of the reference design are presented below RO1AN1212EU0101 Rev 1 01 Page 8 of 18 Dec 03 2012 RENESAS RX210 Single phase Two wire Electricity Power Meter Processor The reference design is using RX210 microcontroller with 32 bit RX processor core It can del
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20. is small a programmable amplifier is used to amplify the signal to use the full dynamic range of the ADC Signal Flow Figure 2 shows the basic signal flow in a 2 wire Energy meter The required parameters to be monitored along with the calculations need to be performed are shown Both voltage and current signals need to be sampled at the same time to do accurate energy measurements Vin O to Vref a KS 12 bit lt gt LCD Displ Power CH Sample and SAR fake S Line Hold ADC Ee Internal Temperature men e Single Line Input Signal Front End Characterstics Reference Signal Processing aoa TA Oversampling x64 Kl SE Vref 1 5V Averaging Load 11 500 mV p p Geng ee Vref 1 5V ADC Input 500 mV for USB both voltage and current MICRO eg i ZigBee Calculations need to be performed V RMS V US V t V t N 1 RMS V Z I t I t N P Active 5 I t V t S Apparent V RMS I RMS Q Reactive v S S P P PF Power Factor P S Signal Acquisition This design uses a single 12 bit SAR ADC to digitize both voltage and current waveforms Voltage and Current need to be sampled at the same time to calculate power This can be achieved if the ADC inputs have a Figure 2 Signal Flow Diagram of Energy Meter RO1AN1212EU0101 Rev 1 01 Dec 03 2012 RENESAS Page 4
21. iver 78 DMIPS 50 MHz with zero wait state program flash RX210 has on chip hardware MAC which greatly assists in signal processing tasks It supports 128 to 512 Kbyte program flash and 20 to 64 Kbyte RAM RX210 supports features like Anomaly detection support for system clock failure flash memory integrity and ADC self check which greatly enhance the meter reliability Measurement interface The reference design supports single phase 2 wire system for energy measurement which needs simultaneous sampling of both voltage and current signals Integrated 8 channel ADC in RX210 with sample and hold circuits on three channels provide this capability Figure 5 shows the analog front end circuit which is used for power measurement This circuit converts line voltage and load current in to low level voltage signals that can be digitized by the ADC A resistor divider formed by R1 R2 R3 and R4 is used to bring down the line voltage to less than 500 mV peak to peak signal This voltage signal is filtered using a low pass filter R5 and C1 and AC coupled before adding a DC offset to make the signal within the ADC measurement range The offset value is equal to the half that of the Vref used by ADC A current transformer CT1 and burden resistor R8 are used to convert high load current in to a voltage signal To achieve the dynamic range required to get accurate measurement of the load current variation a programmable gain amplifier is used to amplify the
22. med within the specified time to effectively use the memory usage and greatly improved with hardware FPU and MAC User Interface The user interface for the energy meter consists of a LCD display and few push buttons to select measured and calculated parameter values on the display The push buttons are not normally required for the production version of the meter The LCD display can be a standard one line or two line LCD segment display or a custom LCD glass with user specified display areas and messages Apart from the LCD display energy meter need to provide light pulses whose repetitive frequency is proportional to the energy parameter specified Normally red LEDs are used to generate these pulses The measurement and calculation software need to have a module which is capable of programming a timer to generate accurate pulses with correct repetitive rate Communication Interface Smart energy meter need to have communication interface talk to handheld computers and as part of smart grid with the central computers Smart grid connectivity is generally provided by wireless and to the handheld readers through RS232 RS485 interface Non volatile Storage The meter needs non volatile storage media like Flash device to store configuration calibration data and archived measurement data to provide trending If the archival is not required then a small EEPROM with 8x1024 bytes may be sufficient Bigger size flash device is required depending on th
23. n higher power consumption and decreased performance Two different types of Memory Flash are available in the RX200 Code Flash for application code and Data Flash with BGO which eliminates the need for external EEPROM or to store additional data tables or system data The BGO Background Operation allows the Data Flash to be programmed while code is executed from the Flash Both Data and Code Flash are programmable at 1 62V making it possible for battery operated devices to program them while running at minimum operating voltage RX210 MCU provides six modular hardware subsystems that help products meet safety standards Clock Accuracy Control checks that the clock frequency is within a predefined range Oscillation Stop Detection switches the chip s main clock to an alternative source if the primary one fails Data Operation Circuit continuously performs a SRAM failure test independently of the CPU The Independent Watchdog Timer I WDT uses a reliable internal clock source ADC has disconnect detection and self diagnostic functions I O pins can read back output values Main features of RX210 which are suitable for energy meter application are e 32 bit RX processor core with 78 DMIPS 50 MHz e Hardware MAC e Zero wait state Flash operating up to SOMHz e 8KB data flash e Built in 8 channel 12 bit ADC with 1pSec conversion time e Sample And Hold circuit available on three ADC inputs e RTC with support for full calendar functionality
24. n the Noise Floor MT 003 Rev A 10 08 WK Analog Devices Inc 5 Walt Kester ADC Input Noise The Good The Bad and The Ugly Is No Noise Good Noise Analog Dialogue 40 02 February 2006 RO1AN1212EU0101 Rev 1 01 Page 17 of 18 Dec 03 2012 RENESAS RX210 Single phase Two wire Electricity Power Meter Website and Support Renesas Electronics Website http www renesas com Inquiries http www renesas com inquiry All trademarks and registered trademarks are the property of their respective owners RO1AN1212EU0101 Rev 1 01 Page 18 of 18 Dec 03 2012 RENESAS Revision Record Description Rev Date Page Summary 1 00 Jun 13 2012 First edition issued 1 01 Dec 03 2012 Page 2 6 12 Changed RX210 series to RX210 Group on page 1 Changed RX200 Family to RX200 Series on pages 2 and 6 Fixed broken link on page 12 General Precautions in the Handling of MPU MCU Products The following usage notes are applicable to all MPU MCU products from Renesas For detailed usage notes on the products covered by this document refer to the relevant sections of the document as well as any technical updates that have been issued for the products 1 Handling of Unused Pins Handle unused pins in accord with the directions given under Handling of Unused Pins in the manual The input pins of CMOS products are generally in the high impedance state In operation with an unused pin in the open circuit state
25. nterested in accurate energy measurement between 1A and 100A In order to meet the total meter accuracy of 1 for example the AFE has to have a better accuracy let s say 0 7 Furthermore the 0 7 accuracy is required for the power measurement which is the product of voltage and current In that case the accuracy requirements for the individual voltage and current will be square root of 0 7 or something around 0 84 To meet the accuracy of 0 84 the ADC needs to have a minimum number of bits called the effective number of bits or ENOB Equation 1 bellow is used to calculate ENOB and it is based on the dynamic range for the current and the accuracy requirements ENOB log Dynamic range AFE accuracy Equation 1 The dynamic range is the ratio between the largest current the meter can measure and the smallest one The largest current in this case is 100A and the smallest one is found from the ANSIC12 20 as 1A Plugging these numbers in the equation above we get the effective number of bits needed to satisfy the 0 55 accuracy for the ADC RO1AN1212EU0101 Rev 1 01 Page 3 of 18 Dec 03 2012 RENESAS RX210 ENOB log 100 1 0 0084 13 54 So the effective number of bits for the ADC to accurately measure energy in the 1 class has to be 14 bits effectively ADC specs are usually listed as resolution and the ENOB is lower due to the contributing error factors such as quantization error nonlinearity error etc As a result the parameter called
26. ntil the target clock signal has stabilized When the clock signal is generated with an external resonator or from an external oscillator during a reset ensure that the reset line is only released after full stabilization of the clock signal Moreover when switching to a clock signal produced with an external resonator or by an external oscillator while program execution is in progress wait until the target clock signal is stable 5 Differences between Products Before changing from one product to another i e to a product with a different part number confirm that the change will not lead to problems The characteristics of an MPU or MCU in the same group but having a different part number may differ in terms of the internal memory capacity layout pattern and other factors which can affect the ranges of electrical characteristics such as characteristic values operating margins immunity to noise and amount of radiated noise When changing to a product with a different part number implement a system evaluation test for the given product Notice 1 Descriptions of circuits software and other related information in this document are provided only to illustrate the operation of semiconductor products and application examples You are fully responsible for the incorporation of these circuits software and information in the design of your equipment Renesas Electronics assumes no responsibility for any losses incurred
27. o ZEN ESAS APPLICATION NOTE RX210 RO1AN1212EU0101 Rev 1 01 Dec 03 2012 Single phase Two wire Electricity Power Meter Introduction This document provides a guide to designing Electricity Meters with Renesas 32 Bit RX210 microcontrollers Typical electricity meter designs today use at least one microcontroller an external analog front end AFE The role of the AFE is to provide accurate voltage and current measurement data to the metrology computation engine implemented some times in the AFE itself or in the microcontroller firmware Depending on the accuracy requirements mandated by industry standards and local authorities additional signal processing tasks such as phase and temperature compensation noise reduction through digital filtering and harmonic analysis may be required Beyond the basic metrology functions smart electricity meters have to be able to calculate and track energy consumption profiles and support automatic meter reading AMR through various communication infrastructure such as wireless or power line PLC etc All these additional functions require more computational resources often provided by additional microcontrollers MCUs or digital program processors DSPs Depending on the features and performance of the MCU s a high level of integration that can be achieved at greatly reduced cost by reducing the number of components used design cycle and system complexity Integrating the AFE function with the computation
28. of 18 RX210 Single phase Two wire Electricity Power Meter hardware sample hold circuits For the hardware which does not have sample and hold signal processing technique called wideband signaling can be used to achieve the same result In this technique samples are taken at a very high scan rate filtered and down sampled Decimation to minimize the sample instance error for power calculation The decimation need to be carried out in software This process is carried out first filtering the output using a FIR filter for each voltage and current channel and performing the decimation To improve the overall measurement accuracy temperature and a fixed voltage reference needs to be measured periodically to track temperature drift and do the necessary corrections The block diagram shows the technique of using the sample and hold circuits to get voltage and current values at the same instance Power calculations The meter analog front end measures only line voltage and load current All the required parameters needed by the energy meter functionality are calculated by using these two values The essential parameters need to be calculated are RMS voltage RMS current Active power Reactive power Apparent power Power Factor and accumulated KWH These values are calculated over a fixed period of measurement and averaged over before display The instantaneous energy calculated is integrated to get accumulated power These calculations need to be perfor
29. of individually momentary push button switches They are connected to different GPIO pins and configured to generate interrupts when key press happens The key press needs to be debounced before presenting it to the process software This is accomplished in the software interrupt service routine Non Volatile Memory The RX210 has 8 Kbyte flash memory for storing data E2 Data Flash It also provides software controlled protection for the data stored in the flash Data can be programmed in units 2 bytes or 8 bytes Erasure is performed in units 128 bytes RX210 has software library to access the data flash and can be integrated in to the firmware to implement the management of configuration calibration and archiving data Power Supply The meter needs to be powered from the line voltage Isolation from the line is required in order to connect other equipment like computer etc to the meter The power supply needs to generate 3 3V required by RX210 microcontroller A simple transformer less power supply can be used and isolation can be provided using opto couplers on the serial communication interface This design is cost effective and serves the purpose RO1AN1212EU0101 Rev 1 01 Page 10 of 18 Dec 03 2012 RENESAS RX210 Single phase Two wire Electricity Power Meter RO1AN1212EU0101 Rev 1 01 Page 11 of 18 Dec 03 2012 RENESAS RX210 Single phase Two wire Electricity Power Meter 4 Software Reference Design The software architecture for th
30. ommunications equipment test and measurement equipment audio and visual equipment home electronic appliances machine tools personal electronic equipment and industrial robots etc High Quality Transportation equipment automobiles trains ships etc traffic control systems anti disaster systems anti crime systems and safety equipment etc Renesas Electronics products are neither intended nor authorized for use in products or systems that may pose a direct threat to human life or bodily injury artificial life support devices or systems surgical implantations etc or may cause serious property damages nuclear reactor control systems military equipment etc You must check the quality grade of each Renesas Electronics product before using it in a particular application You may not use any Renesas Electronics product for any application for which it is not intended Renesas Electronics shall not be in any way liable for any damages or losses incurred by you or third parties arising from the use of any Renesas Electronics product for which the product is not intended by Renesas Electronics 6 You should use the Renesas Electronics products described in this document within the range specified by Renesas Electronics especially with respect to the maximum rating operating supply voltage range movement power voltage range heat radiation characteristics installation and other product characteristics Renesas Electronics shall have no liability
31. ompliance with applicable laws and regulations 9 Renesas Electronics products and technology may not be used for or incorporated into any products or systems whose manufacture use or sale is prohibited under any applicable domestic or foreign laws or regulations You should not use Renesas Electronics products or technology described in this document for any purpose relating to military applications or use by the military including but not limited to the development of weapons of mass destruction When exporting the Renesas Electronics products or technology described in this document you should comply with the applicable export control laws and regulations and follow the procedures required by such laws and regulations 10 It is the responsibility of the buyer or distributor of Renesas Electronics products who distributes disposes of or otherwise places the product with a third party to notify such third party in advance of the contents and conditions set forth in this document Renesas Electronics assumes no responsibility for any losses incurred by you or third parties as a result of unauthorized use of Renesas Electronics products 11 This document may not be reproduced or duplicated in any form in whole or in part without prior written consent of Renesas Electronics 12 Please contact a Renesas Electronics sales office if you have any questions regarding the information contained in this document or Renesas Electronics products or if you have
32. signal The PGA is programmable using SPI port Its gain can be set anything from 1 2 5 10 20 50 100 or 200 which gives a dynamic range of 1 200 The PGA reference input is set at the half the value of Vref used for the ADC which makes the output signal compatible with RX210 ADC input Further the signal is passed through a low pass filter before connecting to ADC channel 00 RX210 ADC channels 00 and 01 have sample hold circuits which enable simultaneous sampling of the signals In addition RX210 has internal voltage reference and temperature sensor These can be monitored periodically for calibration and temperature drift compensation to improve the accuracy Veo DC l o OFFSET L Noo ADDITION Voltage Divider Low Pass Filter 117 VAC 4 R6 R1 R2 R3 i er R5 o eS a et R7 sl RX210 B SPI aie Gee eg Transformer Low Pass Filter gt Programmable A00 BURDEN Gain 6 i Be RESISTOR Amp i i PGA113 E i cT1 l LOAD EE b Gain 1 2 5 10 20 Vref 2 50 100 200 Figure 5 Analog Front End for RX210 based Energy Meter Voltage divider for measuring line voltage is calculated such that high line voltage which 15 higher than 117 VAC produces 500mV peak to peak signal Current transformer used has 10A RMS maximum rating and R8 is calculated RO1AN1212EU0101 Rev 1 01
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