Meeting world market requirements

The demand for solid-state electricity meters is growing worldwide at ever-increasing rates, justifying more specific solutions for different market requirements. In addition, different markets require different information such as kWh, kVARh, kVAh and tamper indication.

The metering function of a meter is normally contained in the integrated circuit. This metering chip does not contain any intelligence, but measures the power of energy consumption and makes this information available to a micro-controller.

In general solid-state meters can be divided into two categories – micro-controller based meters; and the electronic meters with an electromechanical display.

Micro-controller-based meters

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A micro-controller-based meter consists of the metering electronics and a micro-controller, which usually drives an LCD display. The micro-controller allows for flexibility in the application and the incorporation of different features. Calibration can be done in the micro-controller software, where the calibration constant and other meter parameters are stored in EEPROM. The metering electronics consist mainly of the measuring integrated circuit, which makes the measured information available to the micro-controller for further processing (see Figure 1).

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The SA2002H is suitable for kWh metering, and generates a pulse output with the frequency proportional to the power consumption. It has an integrated oscillator, which is available on all of the SA2000 series products. Other markets, however, may require additional parameters or functions; for instance, where energy theft is common, the requirement may be for tamper detection.

Figure 2 shows the block diagram of the SA 2007H, which has two current sensor inputs. For each current sensor input there is a corresponding pulse output. A typical application would be to monitor both live and neutral lines for tamper detection.

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The measurement of active and reactive energy is also a requirement for various markets, both for single and three phase. Figure 3 shows the block diagram of the SA9904B. This three phase integrated circuit measures active and reactive energy, RMS mains voltage, the mains frequency and has an integrated SPI interface for communi-cation with the micro-controller. In addition to kWh and kVARh measurement, a small algorithm can be implemented in the micro controller to calculate kVAh. The SA9903B is available for single phase applications.

There is also a demand for a three phase pulse output integrated circuit where the direction of each individual phase is required. In the case of the SA9605A would be suitable, or if the requirement was for the sum and direction of all three phases, the SA2005F would be applicable.

The electronic meter with an electromechanical display

This type of meter is popular in many countries. A mechanical counter provides the display and storage function for the consumed energy. The meter reading can take place even if the display is not powered.

Since a micro-controller is not used, the metering integrated circuit takes on a new role. It normally consists of a one-chip solution, this being the most cost-effective for this type of meter. The metering circuit’s output has to drive the mechanical counter or stepper motor directly, and provide a pulse or LED output so that the meter can be calibrated, which is done by using external resistor networks or potentiometers.

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Some markets – notably meter manufacturers producing large volumes of meters every day – require a fast calibration time. Here the meter has to be calibrated using only two pulses (see Figure 4). The time between the two pulses is measured, so it is important that the output pulses are stable. This is achieved using the SAMES SA2102D.

Some countries require anti-tamper features, such as correct metering even in the case of earth return or where the connections to the meter terminals are swapped. ICs for this application provide for two current sensors, one for live and the other for neutral. Metering is taken from the wire where the highest power consumption is measured, even if the difference is less than 1%. The different tamper conditions are indicated on outputs, which are connected to indicator LEDs (see Figure 5).

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Electronic meters with electromechanical displays are not restricted to single phase applications. Many markets require three phase meters directly driving counters or stepper motors and showing information such as the measured energy direction, or indicating a voltage failure. In addition some markets require the repeatability of the error measurement to be better than 0.5% at a current of 0.05lb. Using the SAMES SA2005M this repeatability is easily achieved with less than 10 pulses. It will also indicate energy direction, as well as any phase voltage failures (see Figure 6).

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The calibration of the meter is another requirement defined by certain markets and requires that no potentiometers or resistor networks be used.SAMES has a new generation of ICs, both for single and three phase meters, which can be configured from an external EEPROM. Meters based on these new ICs allow for fully automated configuration and calibration during the calibration stage, which reduces costs and increases reliability.

Figure 7 shows the dual current sensor meter, using the SA2007P and a low cost EEPROM to store calibration and configuration data. The kilowatt hours are accumulated in an electromechanical register, which acts as display and memory. The power supply circuit is not shown.

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It is important for the integrated circuit manu-facturer to adapt quickly to the markets' different requirements, while at the same time keeping the integrity of the metering element itself. SAMES has achieved this by keeping the same analogue front-end building blocks throughout, and by adding peripheral features using digital circuitry. This gives customers the comfort of tried and tested circuitry installed in millions of meters used by many meter manufacturers worldwide.

It is important for the integrated circuit manu-facturer to adapt quickly to the markets' different requirements, while at the same time keeping the integrity of the metering element itself. SAMES has achieved this by keeping the same analogue front-end building blocks throughout, and by adding peripheral features using digital circuitry. This gives customers the comfort of tried and tested circuitry installed in millions of meters used by many meter manufacturers worldwide.