IEC TR 61902:1998 pdf download – Household microwave ovens – Visual clarity of see-through oven doors

IEC TR 61902:1998 pdf download – Household microwave ovens – Visual clarity of see-through oven doors.
The tests outlined here may also be applicable to ranges and other household appliances where the workload is enclosed but visible during the treatment.
2 Normative reference
The lolkwing normative Gocument contains provisions which, through reterence in this text. ConStitutOS provisions of this Technical Report At the time of publication, me edition indicated was valid. API normative documents are subject to revision, and parties to agreements based on this Technical Report are encouraged to Investigate the possibdity of applying the most recent edition oP the normative document indicated below. Members of IEC and ISO maintain registers of currently valid International Standards.
IEC 60705:1988, Methods for measuring the performance of microwave ovens lot’ household and similar purposes
3 General
The visibility into microwave oven cavities may be a performance factor 04 interest to the user. Many heating operations are of short duration and the user normally remains in the vicinity of the oven when it is operatmg. Boiling and similar phenomena may begin and become vigorous within a very short time. The appearance of browning ii microwave combination ovens is another phenomenon which may be important to follow.
The viewing screen of a microwave oven shall not allow microwave leakage and must therefore provide an efficient path for the microwave wall currents In the cavity. The metal surface needed for this Is normally either a meshed metal grid or the remaining metal plate parts in a hole screen. For protection and cleaning purposes, there are also glass plates or similar, both in Pront of and behind the metal screen. All these components limit the visibility through the door by reduction of light transmission and by patchiness due to the hole pattern, as well as reflection of external light by the screen and its glass cover. There are also other contributing (actors listed below but not included in the technical measurements.
The term visual clarify expresses the contrast resolution and colour saturation of the image of the food load In a microwave oven cavity br in a conventional oven) seen through the viewing screen. As indicated by the word visual, the clarity is mainly a subjective expression. As a consequence, ranking of ovens may be made by panel testing but some conditions are specified. The test room specifications are given in 4.4. Other requirements for panel testing are given in clause 7.
A more technical series of tests using instruments and physical measurements is specified in clause 6. Results are reproducible but the relevance of the test condilions and specifications the representativity of the test – may be limited because of differences in the common external conditions. There are also some additional factors which influence the real and perceived visual clarity but are not included in the technical tests since they are too complicated. However, such additional factors are automatically included in a panel test. Their relative influence on the test results becomes subjective and varies with ambient lighting conditions.
The additional factors are given below.
• Specularly reflected luminance caused by the outer ass or viewin9 screen. The disturbance to the sight depends very much on the ambient lighting conditions. However. it becomes partially quanhitied by the tact that the specified test room is diutusely ilkiminated.
• The reflectance of the cavity walls and the interior 01 the door. lithe cavity back wall is white the contrast deteriorates in companson with a duN or stainless steel colour. A white inside of the door improves the light intensity in the cavity when the door is closed.
• The colour (whiteness) of the external door area surrounchng the viewing screen. A white area around the outside of a darker viewing screen causes glare phenomena which disturb visual clarity.
• The thickness (hole length) of the screen holes in relation to the hole chanieter. Long length holes with a relatively small in diameter make the viewing sensitive to small oblique viewing angles.
• The size of the viewing screen in relation to the door opening. A small overall viewing screen will reduce the viewing angles and limit the oven placement height.
Some test results and comparisons between lectwilcal and panel tests are given en annex A.
4 Test conditions, material and instrumentation
4.1 LIght source In the cavIty
The light source In the cavity is that provided with the oven. The oven is operated according to clause 8 of IEC 60705 with the cavity lamp(s) operating as In normal operation of the oven but the oven is not operated with microwaves.