By Dave Simpson
Not only have the 1-phase meter requirements evolved to incorporate many more measurement parameters, including kWh, Vmains, Imains, kVAr and kVA, but they may also include time-of-use and maximum demand billing as well as an array of anti-tamper features. On top of this electromagnetic compatibility (EMC) immunity demands have escalated and with the inevitable increase in meter cost, meter life expectancy will also surely increase.
The austriamicrosystems AS8267 and AS8268 1-phase system-on-chip metering ICs provide all the functional requirements for 1-phase LCD meters, including a precision 2-current input measurement front-end, an 8-bit microcontroller, 32 kB of on-chip Flash memory, a real-time clock, up to 96-segment liquid crystal display (LCD) driver, up to 12 programmable multi-purpose inputs/outputs and an on-chip temperature sensor.
With the system integration provided by the AS8267 and AS8268 ICs comes a considerable reduction in the number of external passive components that may be vulnerable to long term drift. Furthermore, the reduced number of solder joints and the inevitable size reduction of the printed circuit board inherently provide for improved system reliability and reduced system cost.
The analogue front-end with its 22-bit resolution analogue-to-digital converters in conjunction with the precision voltage reference provides industry leading accuracy performance of better than 0.1 percent error over a 2000:1 dynamic range. The consistent repeatability of measurements provided by the AS8267 and AS8268 ICs ensures such accuracy performance is achievable in volume meter production. The option of on-chip digital calibration is also available with the AS8267 and AS8268 ICs, providing meter manufacturers with a faster meter production cycle.
Software reliability is given through the highly reliable austriamicrosystems Flash memory technology. Unsurpassed temperature performance of the on-chip Flash memory operating over a temperature range of -40OC to +125OC ensures over 20 years of data retention, even at +125OC. Furthermore, the innovative system design allows for absolute security of both programme and data through a combination of password protection and an attack counter. The AS8267 and AS8268 ICs also provide a facility for an additional external EEProm for data storage. The external EEProm is directly accessed by the industry standard on-chip 8-bit 8051 microcontroller (MCU). The external EEProm is connected via a dedicated serial interface; thus none of the available programmable inputs/outputs is required for this function.
Additional features of the AS8267 and AS8268 ICs include two universal asynchronous receiver transmitters (UARTs) for external communication, a programmable energy LED pulse output, precisely representing the measured energy data, an on-chip real time clock/calendar (RTC) trimmed to ±1.4 ppm, with two alarm registers for complex tariff applications and an on-chip temperature sensor.
The inputs/outputs (MPIO) are programmable for data direction, pull-up or pull-down resistors and drive strength of up to 8 mA. This enables direct connection of LEDs to any of the MPIOs for display of reverse current, phase availability and earthing of the load, and all other standard display requirements such as energy LED pulse output for calibration and consumption monitoring. The fully programmable onchip liquid crystal display driver (LCDD) can also be used to display tamper conditions. The tamper conditions can be recorded with time and date stamp.
The AS8267 and AS8268 ICs allow for more compact and thus more reliable meters at reduced meter system cost and fulfil the inevitable outcome of improved reliability. The end result is a reduced meter lifetime cost for the utility companies.
The AS8268 provides for up to 96 LCD segments and 12 programmable inputs/outputs, while the AS8267 offers a lower cost option for meters requiring up to 80 LCD segments and 9 programmable inputs/outputs. The AS8267 and AS8268 ICs are available in a LQFP-64 pin package and are pin compatible with the already established AS8218 and AS8228 ICs.