AC Energy Metering: A Single-Phase Energy-Metering IC with Autocalibration from Analog Devices

The ADE9153A from Analog Devices is a single-phase energy-metering IC that includes autocalibration.

Analog Devices recently released the ADE9153A, which is a 5 × 5 × 0.75 mm 32-lead LFCSP (leadframe chip scale package) IC capable of taking highly accurate single-phase AC energy measurements. The device is highly integrated, as shown in the diagram below. The energy measurements are performed with the help of a current-sensing component (a shunt resistor or a current transformer).

Typical application circuit for the ADE9153A. Diagram taken from the datasheet (PDF).

To ensure consistent and accurate measurements, over time, the ADE9153A utilizes a technology that Analog Devices refers to as mSure; it’s touted as being an autocalibration technology that provides "accuracy monitoring and self diagnostic" capabilities. mSure allows a meter to automatically calibrate current and voltage channels without using other accurate, or calibrated, sources or reference meters. Seems like magic.

 

Analog Devices' mSure technology, which is integrated into ICs, provides accuracy monitoring and self diagnostics. Image courtesy of the mSure flyer (PDF).

Measurements and Calculations

This IC appears to be quite powerful given all the various measurements and calculations that it’s capable of performing. Besides taking AC line current and line voltage measurements, this IC also provides a host of other AC line-related data, including the following:

• active energy, reactive energy, and apparent energy measurements and calculations;
• current and voltage RMS calculations; and
• zero-crossing detection, peak detection, and dip and swell indication.

To learn more about these measurements and others, check out the seven pages in the datasheet that discuss these topics, starting on page 22.

High-level diagrams of how various measurements are taken, and of the IC's inner workings. From the datasheet (PDF).

Autocalibration Trade-offs: Duration vs. Current Consumption

The mSure autocalibration feature can be operated in one of two power modes: normal mode and turbo mode. Determining which one of these power modes is best suited for an application involves a trade-off: how quickly the autocalibration needs to be completed (which the datasheet calls the speed of convergence) vs. current consumption.

According to the datasheet, in the section entitled mSure Autocalibration Feature (on page 21), turbo mode’s speed of convergence is four times faster than that of normal mode and the current consumption is only two times higher, as shown in the diagram below. Unfortunately, the diagram introduces some confusion due to its use of the terms "normal mode" and "low power mode" in place of "turbo mode" and "normal mode," respectively. (This is really rather odd considering that the datasheet paragraph immediately before the diagram uses "turbo mode" and "normal mode.")

The mSure autocalibration trade-off: duration vs. power consumption. From the datasheet (PDF).

Now, while I personally have never worked in the public utility arena, or in any other energy-producing or energy-transportation industries for that matter, I'm wondering two things:

1. Just how often does such equipment require calibration? I'm thinking maybe once a month at most.
2. Given the apparently small amounts of power required for this autocalibration feature (regardless if it's turbo mode or normal mode), does this seemingly minute amount of current (compared to the vast amounts of current on the grid) really matter? It all seems like splitting hairs to me.

Another puzzling aspect of this issue is that turbo mode is both faster and, if you consider the overall power consumption, more energy-efficient. The current consumption is twice as high, but it converges four times more quickly. In other words, the total current consumed by a turbo-mode calibration is half of the total current consumed by a normal-mode calibration. The only advantage of normal mode, then, is that the instantaneous current is lower. Why would this be a significant advantage?

Do you have any insights on these matters? If so, please share your thoughts on this topic in the comments section below.

Communications

The IC provides two methods of accessing the measured data. One is via the SPI bus, which can run at speeds up to 10 MHz, and the other uses a UART interface that can operate at baud rates of either 4800 or 115,200. For more information on these two forms of communication, check out the datasheet section entitled Accessing On-Chip Data (page 30).

Arduino Shield Evaluation Board

Analog Devices offers an evaluation board (called the EV-ADE9153ASHIELDZ) that is compatible with the Arduino Uno, the Arduino Zero, and the ESP8266. This is handy if you're interested in taking high-voltage AC energy measurements, without first designing a new high-voltage PCB.
Analog Devices has included, within the eval board's user guide, a section (entitled Line Voltage Connections) that calls attention to the cautions that should be exercised when testing with this evaluation board. Be sure to review that section prior to taking any high-voltage measurements.

The EV-ADE9153ASHIELDZ is a high-voltage Arduino-shield evaluation board. Be sure to use caution when testing with this PCB. Image taken from the evaluation board's user guide (PDF).

Have you had a chance to use this new energy-metering IC in any of your designs or its evaluation board? If so, leave a comment and tell us about your experiences.