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Back to Press Release Index
15 April, 1999
Early product development with semi-anechoic chamber facilities.
The changes in regulations and small number of facilities in New Zealand have traditionally meant long lead times and high costs for reputable EMC testing. Due to the lack of competition, and the demand for quicker turn-around times at affordable prices, Underwriters Laboratories has expanded its EMC capabilities to include both radiated and conducted radio frequency immunity testing.
The construction of the South Island's only semi-anechoic chamber will allow Underwriters Laboratories to provide fully compliant radiated testing to national and international radiated immunity standards. Use of these facilities will be of particular significance to New Zealand's electrical and electronic manufacturers, who will be able to utilise them for early product development. This early development will ensure that the tested products comply with all the standards' requirements at an early stage, allowing the products to placed on the market more quickly.
What is EMC?
Electromagnetic compatibility (EMC) ensures that equipment is capable of functioning effectively and satisfactorily in its working environment without causing intolerable electromagnetic disturbance to other pieces of equipment that share the environment.
Electromagnetic interference (EMI) is interference that is radiated in free air or conducted via cables by a piece of equipment or a natural occurrence. Some examples of EMI are:
| Man-made |
Natural |
| Transmitters |
Lightning |
| Moving surfaces |
Electrostatic
discharge |
| Cable carrying
power or signals |
Sunspots or
radiation |
| Electrical or
Electronic equipment |
|
Electromagnetic susceptibility (EMS) is the immunity of a piece of equipment to natural or manmade EMI. It is possible to design a piece of equipment that is completely immune to the effects of all manmade and natural EMI, but due to the high costs involved in design and production, it is not practical or necessary to go to this extent. Standards are set to prescribe the levels of immunity required for the safe operation of electrical or electronic items. Manufacturers of these products in New Zealand are required to have their products tested to the level stated in the relevant standard.
EMS testing is achieved by subjecting a product to simulated man-made or simulated natural EMI. Man-made or natural EMI simulated at Underwriters Laboratories includes:
- Lightning simulation - Surge testing
- Electrostatic discharge - ESD testing
- Switch arcing - Fast transient testing
- Electrical or electronic equipment - Conducted emission
- Blackout / Brownout - Voltage dip and fluctuations
- Harmonic injected into mains - Harmonics testing
- Influences to magnetic fields - Pulse or power frequency testing
- Transmitters - Radiated immunity
- Cables carrying power or signals - Conducted immunity
What is a shielded semi-anechoic chamber?
A shielded semi-anechoic chamber is a room that allows radiated and conducted immunity testing to take place without disturbing or being disturbed by the environment outside of the room. The room is double shielded and designed to act as a Faraday cage to external radio frequency sources and also to ensure that the radiated radio frequency energy is kept within the room.
The South Island's only semi-anechoic chamber, designed by Underwriters Laboratories, is lined with radio frequency foam absorbers and has ferrite tiles on the floor. This serves to dampen reflections and resonance's so that a uniform test field can be generated within the chamber. Underwriters can perform conducted immunity tests on products up to 1m x 1m x 3m high, from 150kHz to 230MHz at 10V and radiated immunity tests from 80MHz to 1000MHz at 10V/m at 3m, or higher at a closer distance. The semi-anechoic chamber ensures repeatable and reproducible results.
The chamber, which can also be used for development radio frequency emission testing, is available to manufacturers for development work or used to provide full compliance testing.
Why test a product for radio frequency immunity?
Imagine you are driving down the road in your new sports car. Your new cell-phone rings and before you can answer it, BANG, your driver's airbag goes off! You manage to safely bring the sports car to the side of the road and wonder what happened. Well, in this case your sports car was not immune to the disturbance given off by the cell-phone. This case has actually happened along with many other similar instances.
If the sports car had been sufficiently tested for susceptibility to the radio frequency interference given off by the cell phone then this incident would not have occurred.
A number of 1998 production model vehicles were recalled due to their susceptibility to ESD. ESD was causing the passenger side airbag to go off. Due to our ever-increasing use of electrical and electronic equipment in everyday life, product immunity is very important for human safety. Imagine what would happen in a hospital if all of the electronic equipment was not immune to outside influences or even each other.
Why test a product for conducted immunity?
A product conducting a disturbance back down the mains or through cables causes conducted disturbance. A classic example of conducted disturbance was illustrated through the use of older hairdryers. When the dryer was switched on, it would conduct noise back into the mains cable and this noise could be picked up by a radio as static or as lines on a TV. In order for a product to be immune to this type of disturbance, it is tested for conducted immunity. The standard establishes levels of degradation of the product during testing, if any. Some products may be less susceptible to conducted disturbances or radiated disturbances than others; the level is dependent on the design and type of the product.
For more information contact: Manuel Shimasaki, General Manager - Underwriters Laboratories.
Phone (03) 339 1607, Fax (03) 339 1671 or email enquiries@parksidelabs.com.
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