Achieving the Potential of Sensors in Smart Meters

E-mail Amanda Milewski

The smart meter and its technology are advancing rapidly with the aid of sensors. What was once a simple analog device is now a sophisticated piece of electronics that incorporates metrology, microprocessor control, and several wireless technologies. Today's smart meters need sensors to help perform several useful and needed functions, driven by the meters' ever-increasing complexity. With utilities and consumers requiring smarter, more reliable, and more cost-effective meters, sensors are evolving to help next generation meters meet these needs. The cutting-edge technology found in today's advanced, compact sensors only increases the role these components play in the smart meter market.

Smart Meter Basics and the Market
A smart meter is the key component of the Smart Grid that enables utility companies and consumers to better monitor, conserve, and control their energy usage. They are designed to enable two-way communication from a home/business to the utility, providing interval energy consumption data and time-of-day pricing information to end-users.

If you don't already have a smart meter installed in your home or business, you soon will. According to Pike Research, an estimated 21 million smart meters were installed in the U.S. in 2010. With more than 90 utilities deploying additional smart meters, expect that number to jump to almost 58 million more smart meters in the near future. As the U.S. moves towards a smarter electrical grid, the functions of these meters will need to become more reliable and robust.

Sensors and Smart Meters
There are several types of sensors that can be found in smart meters, including accelerometers, Hall sensors, anisotropic magneto resistance (AMR) sensors, reed sensors, shock sensors, and thermistors. These sensors allow the meter to have new functions—such as tamper detection, a hidden switch to change meter operating modes, and PCB temperature sensing—and permit current functions to become more reliable, smaller, and cost-effective, in turn making the whole meter more robust and cost-effective. The key to assuring these functions operate to their full potential however, is choosing the right sensor for the job.

Having the ability to identify when tampering is occurring will improve the accuracy of the meter reading. The meter can record the tamper action, which can then be investigated to correct the issue. For tamper detection, one sensor option is a piezoelectric shock sensor that generates an electric charge or a voltage that is proportional to the applied acceleration. If the meter is shaken, moved, etc., the shock sensor can detect this movement and produce a signal output.

The function that enables switching between meter modes provides easy maintenance for the meters by allowing the operator to alternate between the operation display mode and the maintenance display mode. One way to achieve this is to use a hidden switch in the meter, so called because the meter doesn't have an actual switch or any other input device externally visible. An AMR sensor can be used to implement a hidden switch. This noncontact device with 1.5 mT-level sensitivity generates a signal when a magnet is passed over it. The generated signal is then used to toggle the meter's display between modes. Unlike a Hall sensor, the AMR sensor does not need the sensor and magnet to be aligned with pinpoint precision. The AMR sensor has a greater degree of flexibility for the position of the magnet due to its wider detection range and its bidirectional operation with respect to magnetic field direction. Choosing these attributes in a smaller sensor enables greater placement flexibility to smart meter design engineers.

For temperature sensing and over current protection of the PCB, one option is to use a thermistor, which are available in through hole or surface mount designs for both PTC and NTC thermistors. NTC thermistors can be used to help monitor the temperature of various thermally sensitive components on a PCB, while PTC thermistors can be used for circuit protection by detecting over current or overheating of the PCB and shutting the circuit down if necessary. A new breed of long-lead thermistors has been developed that use existing chip NTC/PTC thermistors, which allows for excellent accuracy and low cost. The long leads allow for greater flexibility in placing the thermistor closer to the area of thermal interest.

The Future Looks Bright
As the smart meter market expands and smart meter technology advances, it is anticipated that consumer demand for remote energy control will grow exponentially. With this need comes the challenge of designing low-cost, reliable smart meters that feature robust functions, such as tamper detection, switchable operating modes, and PCB temperature sensing. Thankfully, sensors, such as AMR sensors, shock sensors, and thermistors, are already helping designers not only meet, but exceed consumer demands.

Amanda Milewski, BSEE, is a senior product engineer at Murata Electronics North America, Livonia, MI. She can be reached at 734-742-2041, [email protected].