Black panel thermometer

An industrial standard method has been developed to test the lightfastness of polymers in accelerated test equipment [103]. The apparatus consists of a quartz-xenon tube with a special optical filter between the light source and the specimen to produce light that resembles window glass-filtered daylight [104], Samples are mounted at a specific distance from the arc and are supported on a frame which revolves around the arc 1 to 5 times per minute for uniform exposure. A blower unit in the base provides a flow of air which makes it possible to maintain a black panel temperature of 45°C, measured by a black panel thermometer which is positioned at level with the samples. A black panel unit consists of a bimetallic thermometer mounted on a steel frame. Both faces of the frame plate and also the stem of the thermometer are coated with a heat-resistant glossy black enamel. The relative humidity level in the exposure cabinet is closely controlled. 

The temperature of exposed samples is dependent on both the air temperature in the cabinet and the absorbance of direct radiation. Temperature is usually measured with a black panel thermometer, which gives the surface temperature of a perfectly absorbing material. White panel thermometers are also commonly used which measure the other extreme. The actual temperature reached by a test piece depends on the material and its colour. It will also depend on the air temperature and velocity so that both the air and black panel temperatures should be controlled. ISO 11403-3 [23] defines three sets of conditions in air with the black standard temperature at 65 °C (ISO 4892-2 Method A [27]), behind glass at the same temperature (ISO 4892-2 Method B [27]), and behind glass at 100 °C. 

Because it is not practical to monitor the surface temperature of individual exposed samples, a specified black-coated flat plate sensor — so-called black panel thermometer (BPT) — has been used for decades to measure and control temperature on the sample surface in material testing. Currently, a so-called black standard thermometer (BST sometimes called insulated black panel thermometer in the... 

A tanperature measuring device consisting of a metal panel, having a black coating that absorbs all wavelengths uniformly, with a thermally sensitive element firmly attached to the center of the exposed surface. The black panel thermometer is used to control a laboratory weathering device and to provide an estimate of the maximum tanperature of samples exposed to a radiant energy source. 

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The actual relationship of aging influences, in which room air temperature and specimen wetting also play a role, can be seen in the comparative data for average hourly irradiation in xenon arc lamp equipment. Table 2.13. Besides the irradiation values, black standard temperature data are indispensable for stating weathering conditions, ft represents the temperature that results on the surface of a black coated metal plate mounted in the same position as the specimen in the device (black panel thermometer). 

Samples with different colored or even white surfaces show different deviations to the black standard temperature. A so-called white standard thermometer (WST), indicating the lowest surface temperature of a sample whose surface is directly absorbing and reflecting (also described in the basic ISO standard), can be used. Alternatively, a white panel thermometer (WPT) may be used. The temperature of samples with colored surfaces ranges between the black and white standard temperatures. Constant black and white standard temperatures under given exposure conditions during a test indicate constant surface temperature of any exposed sample — even if, in the field of pharmaceutical substances, the real surface temperature of specifically prepared samples may be above or below the characterizing standard temperatures. 

The absorption ratio of various materials differs greatly. However, knowing the upper and lower limit is sufficient for making an estimate. Under otherwise identical conditions, an object whose absorption ratio is 1 will exhibit the greatest rise in temperature compared to its surroundings, while one with an absorption ratio of 0 will heat up least. In materials testing, black and white panel thermometers have proved to be useful in... 

The temperature that a thermometer with an almost black bulb indicates when it is placed near the heating panel (Fig. 8.51) is practically the same temperature that a human being will feel in the neighborhood of the panel. 

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