Control and connectivity considerations in the design of smart meters by Jonathan Page, MSC Gleichmann

The early implementation of automatic meter reading (AMR) allowed utilities to read meters remotely for billing purposes. This provides data when it is needed without the cost of employing meter readers or having to rely on consumers or businesses to supply meter readings. The move to an advanced metering infrastructure (AMI) introduces two-way communications enabling the control of equipment and appliances. For example, at times of high demand, an electricity provider might balance loads across the network by turning off appliances like freezers for short periods, avoiding the cost of bringing on-stream more expensive generating plant. While the advantages for suppliers are obvious, the intent of smart metering is to provide similar benefits to customers enabling them to both monitor and control their usage.

The purpose of this series of articles is to look at aspects of smart meter design that relate to: local control, sensor interfaces and remote connectivity.

Part 1 - The human face of smart meters

Whether for electricity, gas, heating or water metering the architecture of most smart meters is very similar, with a microcontroller (MCU) at its heart, connected to appropriate measurement sensors and with interfaces to local controls / display and the remote network (see figure 1).

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Figure 1: Architecture of a typical smart meter


Replacing traditional meters with smart meters does not normally change the location of the meter, which is typically where the service enters the premises. Neither does it seem to change the conventional requirement to provide readout at the meter as this provides a fallback in the event that remote access is not possible. But the capability of smart meters does allow for local monitoring and control in a more convenient location within the premises. This then opens up the possibility of a common metering terminal for all services.

Many traditional meters use geared mechanical dials to display energy usage: an electricity meter uses induction to rotate an aluminum disc that, in turn, drives the dials; in a gas or water meter a rotating vane does the same thing. More recent meter designs use electronic sensors and LCD displays. The benefit of mechanical dials is that they are effectively self-powered. A solid-state electricity meter can also be self-powered but gas or water meters typically use a battery to power the electronics, with consequent implications on energy consumption. This dictates the use of a simple display that does little more than provide the same digital readout as its mechanical counterpart – see figure 2.


Figure 2: A simple reflective TN LCD in an electricity meter

The power considerations for a smart meter are just as important, so the choice of display is likely to be similar. The lowest power consumption and hence most commonly used LCD is a basic monochrome TN type relying on reflective rather than backlit illumination. This could be a standard 7-segment numeric or possibly a 16-segment alphanumeric display but, given potential production volumes, could be a custom display that incorporates other indicators, for example, showing the units being displayed.

MSC Gleichmann offers a comprehensive range of LCD glasses and a custom design service. Displays of this type are readily connected to the low power microcontrollers used in smart meters, such as the MCUs from Atmel and Renesas, which have dedicated LCD driver/controller interfaces.
The requirement to show different measurement units is probably one of the few reasons to provide any form of input control on a meter. If required this would likely be implemented as a simple, push-button, sealed micro switch. There is more flexibility when considering input controls for a separate monitoring terminal and touch screen technology is rapidly becoming an ergonomic, low-power and cost-effective solution.

MSC Gleichmann has touch screen options from a range of manufacturers depending on the design requirements for the external monitor’s display and controls. Their Hantouch, Gtouch and eTurbo Touch products use 4-wire and 5-wire film-glass, analog-resistive, touch screen technology, which is combined with LCD displays in a range of sizes. It also has surface capacitance touch screens from Dano Tech Co Ltd and projected capacitance touch screens from Zytronic and GE Star Touch. The choice between these various technologies will depend on sensitivity, resolution / accuracy and cost considerations. This is an area where Gleichmann can offer advice and is one of the benefits of buying from someone who can offer products from different manufacturers.

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Figure 3: A typical remote terminal for a smart meter

Separating the human machine interface (HMI) from the meter itself not only makes access to the data more convenient but should provide the enhanced capabilities that help define smart metering i.e. empowering the user to achieve greater energy efficiency by better understanding their energy usage. But achieving this remote monitoring does require a communications path from the meter to the monitor. There are a number of options for this. An easy choice for an electricity meter is to use power line communications technology to transmit data from the meter through the consumer premises wiring to the monitor (which is probably connected to the mains supply anyway). The alternative for other types of meter would be using Zigbee technology, a digital radio communications standard that is targeted at applications that require low data rates and long battery life. Once again MSC Gleichmann has the answers with power line products from Atmel and Renesas and Zigbee devices from Atmel.

Summary

The intelligence that makes a smart meter ‘smart’ complements the primary function of a traditional utility meter. In respect of local monitoring there is still a readout requirement and maybe a need for control inputs. If these are located at the meter then they will be connected directly to dedicated MCU I/O ports. If the monitoring unit is in a separate, more convenient location then it may have added functionality with a more sophisticated display and controls. Its location away from the meter will also dictate the use of a standard wired or, more likely, wireless communications interface to the MCU.

Providing both the in-meter and separate monitoring functions requires a range of components. These include standard / custom TN LCD displays, resistive / capacitive touch screens and RF communication devices. All of these are available from MSC Gleichmann who also offers many of the other components needed for the complete design of all types of smart meter including MCUs and the sensors and other communication devices that we will be considering in parts 2 and 3 of this series of articles.