Safety and performance of automatic controls

This article about the safety and performance of automatic controls was first published in the IEC's e-tech newsletter, June 2006.

In the early 1970s many countries already had established local requirements for protective controls for household appliances, which in many cases were incorporated into legislation.

So when TC72 (Automatic controls for household use) was established in 1970, it faced an uphill battle to resolve the controversies resulting from the broad span of specialized controls within its scope and from the divergent but successful standards already established in various countries.

Today, TC72 looks after industry's needs for international safety standards for automatic controls for use in household appliances and similar equipment such as refrigerators, air conditioners and microwave ovens.

These also concern non-automatic control devices when such are associated with automatic control devices.

TC72 also prepares International Standards operating controls without safety functions, such as room thermostats in addition to standards for protective controls with a safety function, such as motor protectors and liquid level limits, as well as for non-automatic control devices.

Standards prepared by TC72 also address inherent and functional safety, including operating values and the testing of automatic electrical control devices, but that are also extended to industrial purposes when no dedicated product standard exist, such as for central heating, air conditioning and process heating.

Meeting industry's needs was not easy when TC72 began work.

Its first edition of IEC 730 (today IEC 60730-1) was published as a technical report in 1986.

However, following several observations and suggestions made on earlier work to cover several specialized controls in separate volumes, additional parts were developed: Part 1: General requirements and Part 2: Particular requirements format.

The report was converted into an International Standard in 1990.

According to TC72's Chairman, Japp Dammer, "A very important animal is IEC 60730-2-5, which concerns burner control systems." Dammer says such a system is the heart of a gas or oil fired heating appliance and that malfunction can lead to fire or explosion, making it the most potentially dangerous application in a home.

Burner control systems were among the first household applications equipped with safety related software.

Due to the potentiality of electromagnetic occurrences, it was also necessary to introduce electromagnetic compatibility and immunity levels.

These had to be higher than in normal household appliances in addition to specifying possible failures or malfunction of circuit components.

Major benefits of having such parameters mean that, for example, the short circuit mode can be excluded for certain constructions.

This regulation also applies to other electronic limit controls, such as temperature, pressure and liquid level controls.

Main users of TC72's work, besides control and system manufacturers and test houses, are IEC TC62 (Electrical equipment in medical practice), with which TC72 has a strong connection, and ISO TC161 (Control and protective devices for gas and oil burners and gas and oil burning appliances).

Market forces impacting TC72's work include: The changeover to alternative refrigerants (external influence); Electrical, electromagnetic compatibility, functional safety and mechanical aspects; Push for low cost, simple International Standards; and The shorter life cycle of products.

Experts say that controls are becoming smaller and more complicated, especially with products linked by information technology or wireless solutions.

For Dammer, the controls business is worldwide and he stresses that manufacturers are dedicated to seeing not only worldwide harmonized standards but also certification that is accepted everywhere too.

"But this is a very slow process," he says.

Standards developed by TC72 are accepted at the regional and national levels, especially as the TC takes advantage of the IECEE CB scheme and decreasing cost of approvals.

Challenges Today, with the new European Directives on hazardous substances, TC72 is taking the environment into account in its work, notably by replacing mercury switches and certain sensor fluids by other techniques.

TC72 is also considering potential toxicity concerns for the ecological environment.

TC72's current work includes: Updating all of the part 2 standards to Amendment 1 to IEC 60730-1, including the elimination of "in some countries" clauses; Amending the IEC 60730-1 standard in response to market needs; and Implementing into the IEC 60730 series of standards the requirements of the IEC 61000 series (Electromagnetic compatibility).

As for the future, TC72 intends to: Consider IEC/ISO Guides and their impact on the IEC 60730 series and safety requirements for interfaces to be connected to the telecommunications network and other bus systems; and Develop standards to include controls used in industrial environments to recognize that IEC 60730 has been, and is being, used as a standard for some industrial controls.

The TC also plans to continue preparing amendments and respond to proposals arising from the implementation of IEC 60730-1 around the world.

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