Quality & Standards: Measuring Magnetic Fields
The new European standard EN 50366:2003, published under the 73/23/EEC Low Voltage Directive, pertains to manufacturers and marketers of household appliances and similar apparatuses, sometimes referred to HHA devices. The requirement, effective as of Feb. 1, 2006, established a method to show compliance with the European Council Recommendation 1995/519/EC concerning human exposure to low-frequency electromagnetic fields.
EN 50366 defines the testing methodology and establishes the operating condition of electrical devices that fall under the requirements of the standard. Products under this standard must not emit what is considered potentially harmful levels of magnetic energy, as defined in the standard. Many studies have show that prolonged human exposure to magnetic fields can lead to possible health hazards. As household appliances and similar apparatus provide a means for that exposure, the standard offers a conclusive test to evaluate and confirm compliance to the European Council recommendation. The devices that are applicable under this requirement include, but are not limited to, household and similar appliances, restaurant equipment, commercial scrubbers and cleaning equipment, water heaters, fryers, ovens, and amusement devices.
The standard makes no provision for a grandfather clause. This means that any product put onto the market after Feb. 1 must be compliant with this standard. Products already on the market, installed, operating, and in use are considered acceptable under the standard. In other words, if a device is already in a home or restaurant, installed and working, there is no need to test these devices. If a manufacturer or marketer of an applicable product continues to place these items on the market, EU law requires full compliance with all standards. Any new product would also have to meet the new requirements.
The standard is mostly concerned with lower frequency magnetic fields, specifically between 10 Hz and 400 KHz. Frequencies above 400 KHz are considered outside the specific levels identified in this standard. For microwave oven operating frequencies, either EN 60335-2-25 or EN 60335-2-90 takes precedence.
During test, all devices are required to operate at the rated voltage and frequency. Devices having more than one rated voltage are tested at the highest rated voltage, unless the voltage range includes 230V, in which case the device is tested at 230V. For multiphase devices, the device must be tested at 400V. Devices that are supplied power by batteries must be tested with the battery fully charged.
All controls are to be set at the highest rating, and the device must be tested while energized. Devices with pre-set controls are tested under the intended position of the control. Running time is not specified, however, the device must be operated before testing starts for a sufficient period to replicate the conditions the device would see under operating conditions.
It is important to note is that devices supplied with accessories must also be tested. In the case of multiple accessories, the accessory that provides the results in the highest load level must be used. An example of a test set up in shown in Fig. 1.
The measurement methodology involves the use of a magnetic field sensor. The sensor must be placed a specific distance from the operating device, depending on the device and the proximity to the person using or operating the device under standard operating conditions. For example, the measuring distance for a heating pad would be 0 cm, or the sensor placed directly against the heating pad while testing to simulate standard operating conditions. A hair dryer would require a distance from the sensor to be 10 cm, as this is considered a standard operating distance. An oven would require a measuring distance of 30 cm, and a floor polisher would be 50 cm. An example of the measurements required for distance is shown in Fig. 2.
In addition to distance, location and operating conditions are specifically identified on the standard. For a heating pad, measurements must be taken from the top of the pad, with the pad spread out in a fashion that is consistent with normal operating use. The amount of time the pad is to be on is not specified, only that the pad achieve its normal operating mode under its highest setting.
For a hair dryer, all surfaces are to be tested, and they are to be tested while operating continuously under the highest temperature setting. For ovens, measurements are to be taken from the top and the front, as these locations are consistent with normal operator use. The test must be performed with the oven empty, with the door closed, at the highest temperature setting. If the oven has a self-cleaning mode, it must also be tested in this mode. An example of this test is shown in Fig. 3.
For a floor polisher, measurements are taken from all surfaces, and the device is continuously operated at its highest speeds with no mechanical load on the polishing brushes.
Under this standard, the allowable limit for devices that operate between 0.025 kHz and 0.8 KHz is 100 micro Tesla. Since most devices operate at 50 Hz, this limit is determined by 5 divided by the frequency in kHz, in this case the 50 Hz operating frequency. If a device is found to exceed the established limits, a coupling factor may be used to determine compliance. The coupling factors are different for different types of devices. When applied, the coupling factor may show compliance when measured at the device's hot spot and compared to other measurements from the device.
Appliances that are constructed so they can only produce magnetic fields at mains frequency and associated harmonics need only to be tested at the frequency range below 2 kHz. Appliances are considered to meet the requirements of the standards when all of the following conditions are met:
- The currents, including harmonic currents and generating magnetic fields, are known.
- All harmonic currents with amplitudes higher than 10 percent of the amplitude of the mains frequency decrease over the frequency range continuously.
- The magnetic flux density measured at the mains frequency is the less than 50 percent of the reference level specified for the mains frequency.
- The magnetic flux density measured during a broadband measurement over the frequency range, with the mains frequency suppressed, is less than 15 percent of the reference level specific for the mains frequency.
When declaring conformity to this new standard, test data must be included in the technical file. It is often recommended that accredited third party labs perform the tests and provide a formal test report that verifies compliance. This report should identify the model number tested, date tested, testing results, and photographs of the testing being performed. This report should be signed by the proper representative of the lab performing the testing, as well as the approved contact from the company that manufacturers or markets the device. This test report should be added to the technical file for future reference.
When evaluating multiple devices of identical or similar construction, or different models of the same device, a product matrix/alternate construction format may be used. This method utilizes a technical construction file. Initially, the devices must be reviewed to ensure that the similarities among these devices are well defined, and any sub-component differences among the specific models should be scrutinized. In many instances, identifying the model that emits the most energy (based on size, components, or operating features), may make it unnecessary for models of lesser values to be tested, so long as the documentation clearly states the rationality for not testing the additional models.
Household appliances and similar apparatus must legally conform to the new standard, effective Feb. 1, 2006. There is no grandfather clause, and all products placed on the market must legally confirm to the conditions established. This includes new shipments of products that were previously compliant before the new standard went into effect. Tests limits for exposure to electromagnetic field in most cases is 100 micro Tesla. Testing should be performed by an accredited third party laboratory, and all updated test reports and findings should be placed in the technical file. A product matrix/alternate technical construction file may be used for similar models of a single product. All test reports and declarations of conformity must include the signature of a proper representative of the manufacturing or marketing organization that places the product on the market.