Testing of Microwave Ovens as per IEC 60335-2-25 and IS 302 Part 2 Sec 25
Microwave oven (commonly referred to as a microwave) is an electric oven that heats and cooks food by exposing it to electromagnetic radiation in the microwave frequency range. This induces polar molecules in the food to rotate and produce thermal energy in a process known as dielectric heating. Microwave ovens heat foods quickly and efficiently because excitation is fairly uniform in the outer 25–38 mm (1–1.5 inches) of a homogeneous, high water content food item.
Hazards in a Microwave Oven
- Temperature Hazard: Water and other homogeneous liquids can super-heat when heated in a microwave oven in a container with a smooth surface. That is, the liquid reaches a temperature slightly above its normal boiling point without bubbles of vapor forming inside the liquid. The boiling process can start explosively when the liquid is disturbed, such as when the user takes hold of the container to remove it from the oven or while adding solid ingredients such as powdered creamer or sugar. This can result in spontaneous boiling (nucleation) which may be violent enough to eject the boiling liquid from the container and cause severe scalding.
- Metal Object:Any metal or conductive object placed into the microwave will act as an antenna to some degree, resulting in an electric current. This causes the object to act as a heating element. This effect varies with the object’s shape and composition, and is sometimes utilized for cooking.
- Direct Microwave Exposure: Direct microwave exposure is not generally possible, as microwaves emitted by the source in a microwave oven are confined in the oven by the material out of which the oven is constructed. Furthermore, ovens are equipped with redundant safety interlocks, which remove power from the magnetron if the door is opened. This safety mechanism is required by United States federal regulations. Tests have shown confinement of the microwaves in commercially available ovens to be so nearly universal as to make routine testing unnecessary.
- Chemical Exposure: Some magnetrons have ceramic insulators with beryllium oxide (beryllia) added. The beryllium in such oxides is a serious chemical hazard if crushed then inhaled or ingested. In addition, beryllia is listed as a confirmed human carcinogen by the IARC therefore, broken ceramic insulators or magnetrons should not be handled. This is a danger if the microwave oven becomes physically damaged, if the insulator cracks, or when the magnetron is opened and handled, yet not during normal use. The use of unmarked plastics for microwave cooking raises the issue of plasticizers leaching into the food, or the plastics chemically reacting to microwave energy, with by-products leaching into the food, suggesting that even plastic containers marked “microwavable” may still leach plastic by-products into the food
- Uneven Heating: Microwave ovens are frequently used for reheating leftover food, and bacterial contamination may not be repressed if the safe temperature is not reached, resulting in food borne illness, as with all inadequate reheating methods. While microwaves can destroy bacteria as well as conventional ovens, they do not cook as evenly, leading to an increased risk that parts of the food will not reach recommended temperatures
- Interference: Microwave ovens, although shielded for safety purposes, still emit low levels of microwave radiation. This is not harmful to humans, but can sometimes cause interference to Wi-Fi and Bluetooth and other devices that communicate on the 2.45 GHz wavebands; particularly at close range
- Variations: Some microwaves have a “grill” feature that heats a plate or rack to high temperature to sear the outside of food. Some have dual microwave and convection oven functionality, leaving microwave-only appliances to be described as “solo” microwaves.
Main Tests for Microwave Oven
Main tests under Microwave Oven Testing are as follows:
- Power Input and Current
- Heating or Temperature Rise Test
- Leakage current and Electric Strength
- Moisture Resistance
- Mechanical Strength
- Protection against access to live parts
- Transient over-voltages.
- Overload Protection of Transformers
- Endurance Test
- Stability and Mechanical Hazards