The electricity meter is one device that no household connected to the grid can escape, yet the technology utilized by analog meters (the most common type) dates to the late 19th century.
Power engineers have recently developed a solid state electronic meter that sends electricity consumption readings wirelessly. This new meter eliminates human error and allows utility companies to monitor their systems more accurately.
We were always interested in these meters, but had trouble acquiring one for a teardown — it’s not like you can just walk into a Best Buy and pick one off the shelf. Thankfully, the generous folks over at Elster were kind enough to send us one of their REX2 meters for thorough dissection!
- The REX2 meter provides several enhancements over non-programmable meters:
- Nonvolatile memory rated for 1,000,000 write cycles
- Advanced security with full 128-bit AES encryption
- Remote upgradeability
- Support for 900 MHz and 2.4 GHz ZigBee communication
- Optional: flux capacitor add-on???
- Before gaining access to the interior of the meter, you must first break a security seal. Apparently, electric companies don’t want you tampering with their meters. Go figure!
- Who would’ve thunk that your power meter would have a LAN ID? A LAN ID is required to connect to the IP-based EnergyAxis Smart Grid network.
- The true innovation in smart meters is their ability to relay power consumption statistics without direct contact from a meter reader. Our Elster meter accomplishes this by sending encrypted signals on the 900 MHz ISM band.
- Extremely thick copper wires allow the meter to be wired in series with a household’s main power supply. They’re capable of handling 200 Amps!
- Interestingly, the meter relies on a black ring-shaped current transformer installed around the copper wires to send power consumption signals to the main board. Current transformers indirectly measure the current flowing through the thick copper conductors and provide an output that can be read by the electronics on the board.
- Long metal pressure contacts along the inside case of the meter conduct 240V AC electricity to pads that provide power to the main board. No need to plug this unit into the wall outlet.
- In the whole device there is only one screw, a surprisingly difficult to find Phillips #1.
- Main ICs located on the front side of the motherboard include:
- Teridian 71M6531F SoC with an MPU core, RTC, FLASH and LCD driver
- Texas Instruments LM2904 low power dual operational amplifier
- RMFD RF2172 medium-power high efficiency amplifier IC
- Texas Instruments CC1110F32 Sub-1GHz System-on-Chip with MCU and 32kB Flash memory