What Is a Pyrheliometer?

Generally refers to a class of instruments that do not come in contact with a high-temperature object, but use the radiation formula to calculate the temperature of the object by measuring its radiant heat.

Instruments for measuring higher temperatures. Optical pyrometers and radiation pyrometers are the two most important. ^[2]

The most commonly used optical pyrometer is the hidden wire optical pyrometer.

There are two measurement methods: one is adjustment

The other is a photoelectric pyrometer, which has the same basic principle as an optical pyrometer. The main difference is that photoelectric pyrometers use photoelectric conversion devices instead of human eyes to compare brightness, so the measurement results are not affected by human subjective factors. Some photoelectric pyrometers also use photomultiplier tubes as conversion devices, which greatly improves the sensitivity of the instrument, and can perform continuous measurement and automatic recording.

Some photoelectric pyrometers also use interference filters instead of red filters, which improves work

Also called ratio pyrometer or two-color pyrometer, it is a measuring object

Pyrometer principle

Pyrometer based on Stefan-Boltzmann law of heat radiation.

There are two types of radiation pyrometers: refractive and reflective.

The refracting radiation pyrometer receiver is usually composed of a thermopile. The hot end collects radiant energy, and the cold end is room temperature. During the measurement, aim the object to be measured through the eyepiece, so that the image of the object just falls on the "+" platinum plate of the receiver.

Radiation pyrometer

The electric meter indicates the temperature rise of the receiver, and the usual division is marked as the black body radiation temperature value T p. The main disadvantage of this pyrometer is that due to the chromatic aberration when the objective lens is focused, only a part of the radiant energy can be focused on the receiver, causing errors.

Reflective pyrometers use a concave mirror to focus radiant energy onto a receiver for measurement.

The structure is almost the same as that of the refracting pyrometer. Although this pyrometer avoids the error caused by the chromatic aberration of the lens, because the cavity is open, dust easily enters the cavity and needs better maintenance.

Pyrometer application

The radiation pyrometer has the same temperature range and performance as the optical pyrometer.

The measurement errors of radiation pyrometers mainly come from:

The selective absorption effect of the intermediate medium (such as the atmosphere, etc.) makes the mid-infrared part of the radiant energy reaching the receiver lose more;

It is not measured according to the specified distance from the heat source to the pyrometer (usually each radiation pyrometer specifies a ratio for the diameter of the area of the observed surface and the distance between the pyrometer lenses);

The selective absorption characteristics of the receivers in various pyrometers are different, which causes the spectral emissivity to deviate from the selected value; Changes in the temperature of the cold and hot ends of the thermopile, and instrument errors.