Avoiding interference

Work to curtail radio frequency disturbance from electric tools is improving constantly

By Morand Fachot

Electromagnetic compatibility (EMC), the ability of electric and electronic devices and appliances to operate without interfering when close to each other, is important in a world of increasing electrification. Limiting electromagnetic interference (EMI) from electric tools in particular has greatly improved.

Philips EMC chambers EMC testing chamber for electronic components (Photo: Philips)

Less noticeable but not entirely absent

EMI was very perceptible in the past, in particular when radio or TV reception was disturbed as appliances or tools were used nearby. EMI may represent more than a mere annoyance as more electronic devices are found in the modern environment. It can disturb the operation of electronic systems such as medical devices, automotive electronic equipment, computers or air traffic control systems.

EMC, defined in the International Electrotechnical Vocabulary as "the ability of a device, unit of equipment or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment", is important for all electric and electronic devices that create interference as well as for those whose operations can be affected by EMI.

Limiting interference from electric tools, which are operated by electric motors, was particularly important as these were a main source of interference in the past. This has been achieved to a great extent through International Standards developed by CIS/F, a Subcommittee (SC) of CISPR, the international special committee on radio interference.

Getting the right tools

CISPR has a very broad scope for standardization in the field of EMC, aspects of which are addressed by its various SCs.

A CISPR radio disturbance limit is a limit that is recommended to national authorities for incorporation in national standards, relevant legal regulations and official specifications. It is also recommended that international organizations use these limits.

CIS/F prepares International Standards "in the field of limits and particular methods of measurement for control of radio frequency disturbances from (and immunity of) electric motor operated and thermal appliances for (…) electrical tools (…)".

To do this CIS/F developed two International Standards, CISPR 14-1 and CISPR 14-2, relating to EMC – Requirements for household appliances, electric tools and similar apparatus, the first one concerning emission, the second, immunity, which are the two sides of the same EMC coin. (See article on CISPR 14-2 in this e-tech).

Limiting EMI from electric tools is particularly important as these tend to be found everywhere nowadays. They have been used by tradesmen and workshop in the professional environment for a long time but are now found increasingly in a domestic setting as individuals take up DIY tasks made easier precisely by the wider availability of electric tools. (See articles on electrical tools for DIY, and on the safety of DIY tools in this e-tech)

CIS/F standardization work does not cover "apparatus designed exclusively for heavy industrial purposes".

Comprehensive scope

CIS/F covers both sides of the EMC coin. CISPR 14-1 defines radiated emission limits, describes methods of measurement and standardizes operating conditions and the interpretation of results.

Although CISPR 14-1 joins together household appliances, electric tools and similar apparatus in general, it differentiates certain features for electric tools according to the rated power of the motor, i.e. rated motor power not exceeding 700 W; above 700 W and not exceeding 1 000 W; and above 1 000 W. These differences concerning power tools are for disturbance power limits and margins when performing disturbance power measurement in the frequency range 30 MHz to 300 MHz.

As for CISPR 14-2, which is intended to establish uniform requirements for the electromagnetic immunity of the equipment mentioned, to fix test specifications and other criteria, it doesn't differentiate electrical tools. Instead, it subdivides equipment into categories two of which in particular are relevant for electric tools, they are:

Category II, which includes mains powered motor operated tools.

Category III: equipment which in normal use, is not connected to a power network and has no cables attached, includes apparatus provided with rechargeable batteries (…) which can be charged or operated by connecting the apparatus to the mains power.

Standardization work by CIS/F is essential for electrical tools manufacturers as it allows them to make products that are less and less likely to generate electromagnetic interference that can affect other equipment.

right angle drill EMI from this 1949 right-angle Milwaukee drill was certainly higher than that of current tools (Photo: Buyaparcel blog)
Philips EMC Chamber EMC testing chamber for electronic components (Photo: Philips)
Metabo impact drill This Metabo KHE 2650 combination hammer meets the latest EMC standards (Photo: Metabowerke GmbH)