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Chipsets use shunts to measure 3-phase electrical energy

Posted: 09 Jan 2015 ?? ?Print Version ?Bookmark and Share

Keywords:Analog Devices? chipset? shunt? ADC? DC/DC converter?

Analog Devices has recently released the details of a chipset intended for measuring 3-phase electrical energy, using shunts as current sensors. The chipset includes the ADE7978, the ADE7933/ADE7932 and the ADE7923 devices from the company.

The ADE7933/ADE7932 are isolated, 3-channel sigma-delta analogue-to-digital converters (ADCs) for polyphase energy metering applications that use shunt current sensors. The ADE7923 is a non-isolated, 3-channel sigma-delta ADC for the neutral line that uses a shunt current sensor. The ADE7932 features two 24bit ADCs, and the ADE7933 and ADE7923 feature three 24bit ADCs.

ADI chipset

One channel is dedicated to measuring the voltage across the shunt when a shunt is used for current sensing. This channel provides a signal-to-noise ratio (SNR) of 67dB over a 3.3kHz signal bandwidth. Up to two additional channels are dedicated to measuring voltages, which are usually sensed using resistor dividers.

The unused voltage channels on the neutral ADE7923 can be used for auxiliary voltage measurements. These channels provide an SNR of 75dB over a 3.3kHz signal bandwidth. One voltage channel can be used to measure the temperature of the die via an internal sensor.

The ADE7933 and ADE7923 include three channels: one current channel and two voltage channels. The ADE7932 includes one current channel and one voltage channel, but is otherwise identical to the ADE7933.

The ADE7933/ADE7932 include ADI's isoPower, an integrated, isolated DC/DC converter. Based on the ADI iCoupler technology, the DC/DC converter provides the regulated power required by the first stage of the ADCs at a 3.3V input supply. The ADE7933/ADE7932 eliminate the need for an external DC/DC isolation block. The iCoupler chip scale transformer technology is used to isolate the logic signals between the first and second stages of the ADC. The result is a small form factor, total isolation solution. The ADE7923 is the nonisolated version of the ADE7933 that can be used for neutral current measurement when isolation from the neutral line is not required.

The ADE7933/ADE7932 and ADE7923 contain a digital interface that is designed to interface with the ADE7978. Using this interface, the ADE7978 accesses the ADC outputs and configuration settings of the ADE7933/ADE7932 and ADE7923.

The ADE7933/ADE7932 are available in a 20-lead, wide-body SOIC package with increased creepage. The ADE7923 is available in a similar 20-lead, wide-body SOIC package without the increased creepage.

The ADE7978 is a high accuracy, 3-phase electrical energy measurement IC with serial interfaces and three flexible pulse outputs. The ADE7978 can interface with up to four ADE7933/ ADE7932 and ADE7923 devices. The ADE7978 incorporates all the signal processing required to perform total (fundamental and harmonic) active, reactive and apparent energy measurement and RMS calculations, as well as fundamental-only active and reactive energy measurement and RMS calculations. A fixed-function digital signal processor (DSP) executes this signal processing.

The ADE7978 measures the active, reactive and apparent energy in various 3-phase configurations, such as wye or delta services, with either three or four wires. The ADE7978 provides system calibration features for each phase, gain calibration and optional offset correction. Phase compensation is also available, but it is not necessary because the currents are sensed using shunts. The CF1, CF2 and CF3 logic outputs provide a wide selection of power information: total active, reactive and apparent powers; the sum of the current RMS values; and fundamental active and reactive powers.

Tthe chipset can be used in applications such as shunt-based polyphase meters; power quality monitoring; solar inverters; process monitoring; protective devices; isolated sensor interfaces; and industrial PLCs.

- Graham Prophet
??EE Times Europe

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