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Relays and switches play a central role in protecting smart meters against illegal tampering and manufacturers are coming up with new designs to meet European Union directives on reducing consumption of energy-using products, according to an industry expert.

Tamper proof switches, DC power relays and other designs are coming on the market to support the new wave of eco-friendly electronics and energy saving systems required under the EU Ecodesign Directive, said Andries de Bruin, European product marketing manager, Omron Electronic Components Europe.

Latching relays

Latching relays are central to smart meter design, to implement the remote disconnect function required for load management, time of day (ToD) tariff-switching, disconnect and pre-payment,

To achieve low overall meter power consumption, a bi-stable latching relay design with the highest electrical performance is desirable. This is a very specialist application, with very specific requirements, explained Mr de Bruin. Considerations include small overall size to minimise the size of the meter and resistance to tampering using an external magnet.

Remote reset switches

One of the key goals of the Eco-Design Directive is to limit, and eventually eliminate, standby power. Electromechanical switches can completely power down a system, but until now a limitation has been that they need to be manually actuated.

Remote reset switches provide a great solution, drawing no power until they are activated and therefore are helpful in implementing systems that eliminate standby power and meet the European Commission ErP Ecodesign directive, says de Bruin.

Versions of these switches can also address the issue that some systems need to follow a set shut-down sequence to avoid loss of data or circuit damage. For example, capacitors may need to be discharged before a system can be regarded as safely switched off.

To address this, remote reset switches with a delayed off function are available to allow safe shut down of electrical equipment. With such switches, the power to the system is maintained when the switch is returned to the off position. The system is then powered down by an external signal after an interval determined by the designer.

These remote switches are suitable for a range of industrial and consumer electrical applications and even support high inrush currents to TV-8 standards.

Tamper proof switches

Remote reset switches is just one example of the way in which switch design is evolving to address new requirements. For example, an issue with smart meters, industrial control systems and other applications is tamper detection.

A switch is commonly used to detect when the cover of a system has been opened. Smart meter anti-tamper switches may not be actuated for years, but should still operate reliably should the meter be attacked after this period.

Switches for this application, such as a snap-action switch, are designed to support long term operation even with very low switching frequencies. This type of switch incorporates a single-leaf movable spring and an edge shaped fixed contact, which exerts a high contact force per square metre and aids wiping movement keeping the contact surface clean.

De Bruin said: "It is a challenge for electronic designers to ensure that off really does mean off for the systems that they design. The Eco-design directive puts regulatory force behind this need, but truthfully customers are increasingly aware of the cost of energy, and leaving a system powered when not in use can affect its safety and service life too. Human users cannot usually be relied on to turn off equipment when it isn’t required, and some form of automation is required."