Selection of infrared thermometer for high and medium frequency induction heating equipment

Reasonable selection of infrared thermometer plays an important role in ensuring the quality of steel heat treatment. How to choose a thermometer? The following introduces the key points for choosing an infrared thermometer.

(1) Measurement range of temperature The short-wavelength band of the infrared band should be used as much as possible when measuring temperature, because the short-wavelength band is more sensitive and has a short response time. The narrower the measurement temperature range, the higher the measurement accuracy; the wider the measurement temperature range, the measurement accuracy decreases. The induction heating quenching and tempering temperatures should be measured using two thermometers respectively. For example, the quenching thermometer is used in the 800~1000℃ temperature zone, and the tempering thermometer is used in the 250~800℃ temperature zone.

(2) The size of the high-temperature measured target. Infrared thermometers are divided into two types: single color and double color. The monochromatic thermometer requires that the size of the measured target should exceed 50% of the field of view. If the size of the measured target is too small, the radiant energy from the background will enter the thermometer through the optical system, thus affecting the temperature measurement accuracy. If the size of the measured target is larger than the field of view, there will be no problem. During the rapid heat treatment of steel by induction heating, except for the temperature measurement of smaller steel wires, which should pay attention to the target size, there will be no problem in measuring the temperature of other steels. Targets in motion are best suited for infrared thermometers. The above are the things you should pay attention to when using an infrared monochrome thermometer. You don't have to worry about the above problems when using an infrared two-color thermometer, because the temperature measured by the two-color thermometer is determined by the ratio of the radiated energy of two independent wavelengths. When the measured target is very small and far from filling the field of view, or there is smoke or dust blocking the radiation energy at the measurement site, it will not have an impact on the measurement results. For small and moving targets or targets that appear and disappear, a two-color infrared thermometer is a better choice.

(3) Determination of distance coefficient (D:S). The distance coefficient is also called optical resolution. D represents the straight-line distance between the thermometer probe and the measured target, and S is the diameter of the measured target. Due to the limitations of on-site conditions, the thermometer must be installed far away from the target being measured, and the size of the target is small. A thermometer with high optical resolution, that is, a large distance coefficient, should be selected. The larger the distance coefficient, the higher the optical resolution and the higher the instrument cost. Imported thermometers have fixed focus thermometers. The light spot is smallest at the focus, and increases near or far from the focus. In order to measure temperature accurately, when using a fixed-focus infrared thermometer, the size of the target to be measured should be larger than the size of the light spot at the focus. There is also a zoom infrared thermometer. The focus position can be adjusted according to the distance of the measured target. The distance coefficient of the instrument is difficult to increase, and the cost increases, so it is not suitable for use.

(4) Selection of infrared spectrum response value. The wavelength is selected according to the measured temperature. When measuring the temperature of steel in high-temperature areas, a thermometer with a near-infrared wavelength (1.6-2.4um) should be used: for other temperatures, a thermometer with a wavelength of 3 to 5um or 8-14um can be used.

(5)Selection of response time. The response time indicates the reaction speed of the infrared thermometer to the temperature change of the measured target. It depends on the time constant of the photoelectric detection, signal processing and display system in the thermometer. The quick response time of the thermometer can reach Imso. When measuring the temperature of induction heating steel, a thermometer with fast response should be selected. The response time is selected based on the movement speed and temperature changes of the steel. The response time can be relaxed when the forward speed is relatively slow and the temperature does not change significantly.

(6) Environmental conditions requirements for thermometers. The environmental conditions for rapid heat treatment by induction heating of steel are high temperature, water gas and a small amount of smoke and dust (oil quenching). The thermometer is required to have a protective cover and a cooling system (water cooling or air cooling).