Infrared pyrometer intruduction

In the hot summer, with the rise of temperature, the power load of the power grid gradually increases, followed by the increase of line current, equipment high load operation time becomes longer, the temperature rises, and the failure rate increases. The voltage level of the power supply equipment and line is high and the safety distance is long. Therefore, it is difficult to troubleshoot faults. In view of this situation, is there any technology that can conveniently, quickly and accurately find out the abnormalities and defects in the operation of electrical equipment in the first time, so as to prevent minor problems from occurring? The answer is the subject of this article - infrared temperature measurement.

1. Principle of Infrared Pyrometer

Anything above absolute zero is constantly emitting infrared radiation into the surrounding space. The infrared radiation energy of an object and its distribution by wavelength are closely related to its surface temperature. Thus, by measuring the infrared energy radiated by an object itself, its surface temperature can be accurately measured.

2. Infrared Thermometer working principle and use

* Working principle
The infrared thermometer is composed of optical system, photodetector, signal amplifier, signal processing, display and output. The optical system gathers the infrared radiation energy of the target in its field of view, and the infrared energy is focused on the photodetector and transformed into the corresponding electrical signal. The signal is transformed into the temperature value of the measured target after the amplifier and signal processing circuit is corrected according to the algorithm built in the instrument and the target emissiveness.
Compared with the traditional way of temperature measurement, infrared thermometer can detect the temperature of the hot spot in a certain distance, through scanning, can also draw the thermal image of the temperature gradient of the equipment in operation, and high sensitivity, easy to use in the field. It can detect the thermal fault of electrical equipment with high resolution of 0.05℃ in the Wide Range of -20℃ ~ 2000℃, revealing the heating of wire joints or wire clips, and local hot spots in electrical equipment, etc.

* Main points and precautions for use

(1) Use points

A) Determine the temperature range: each type of thermometer has its own specific temperature range, the user's measured temperature range must be considered accurate and comprehensive.

B) Determine target size: During temperature measurement, the measured target area should be filled with the field of view of the thermometer. If the target size is smaller than the field of view, the background radiation energy will enter the thermometer's visual signature and interfere with the temperature reading, resulting in errors.

C) Determine the distance coefficient (optical resolution) : The distance coefficient is the ratio of the distance D between the probe of the thermometer and the target and the diameter S of the measured target. If the thermometer must be located away from the target due to environmental conditions and small targets are to be measured, a thermometer with high optical resolution should be selected. On the contrary, a thermometer with a high distance coefficient should be selected.

D) Determine the wavelength range: in the high temperature region, the best wavelength for measuring metal materials is near infrared, 0.8 ~ 1.0μm can be selected. Other temperature ranges are available at 1.6μm, 2.2μm and 3.9μm. Because some materials are transparent at certain wavelengths and infrared energy will penetrate them, a special wavelength should be selected for this material. Such as the measurement of glass internal temperature 1.0μm, 2.2μm and 3.9μm; 8 ~ 14μm is suitable for low temperature measurement.

E) Consideration of environmental conditions: When the ambient temperature is high and there is dust, smoke and steam, accessories such as protective sleeve, water cooling system, air cooling system and air purifier provided by the manufacturer can be selected, which can effectively solve the environmental impact and protect the thermometer to achieve accurate temperature measurement.

F) Calibration: Infrared thermometer must be calibrated to correctly display the temperature of the measured target. The calibration period is generally one year. If the thermometer is out of tolerance in use, return it to the manufacturer or the service center for re-calibration.

(2) Matters needing attention

A) The infrared thermometer only measures the surface temperature, not the internal temperature.

B) the wavelength above 5um can not be measured through quartz glass, but can be measured through the infrared window, it is best not used for bright or polished metal surface temperature measurement.

C) The instrument aims at the target and scans up and down on the target after spotting a hot spot until the hot spot is determined.

D) The environment such as steam, dust and smoke will block the optical system of the instrument and affect accurate temperature measurement.

E) If the thermometer is suddenly exposed to an environment with a temperature difference of 20℃ or higher, allow the instrument to adjust to the new ambient temperature within 20 minutes.

* Test requirements

(1) General requirements:

A) The equipment being tested is in a state of live operation or power supply or in a state that may cause the surface temperature distribution characteristics of the equipment.

B) Try to avoid closed blocks in the line of sight, such as doors and cover boards.

C) The ambient temperature should not be lower than 0℃, the relative humidity should not be greater than 85%, the daytime weather should be overcast and overcast, the detection should not be carried out under bad meteorological conditions such as thunder, rain, fog and snow, and the wind speed should not be greater than 5m/s. When the environmental conditions are not met, the defect judgment should be cautious.

D) When testing outdoors or during the day, avoid direct sunlight or enter the lens of the instrument through reflection of the subject; When testing indoors or at night, avoid direct light and turn off the light for testing under safe conditions.

E) Detecting the influence of the equipment condition with low load rate on the test results and defect nature judgment should be taken into account when detecting the current heating equipment with rated load of not less than 30% under very low load.

(2) Accurate detection requirements (in addition to meeting the general detection requirements, the infrared diagnosis of electrification equipment should also meet the requirements)

A) Wind speed not greater than 1.5m/s;

B) The power-on time of the equipment is not less than 6h and should be greater than 24h;

C) During outdoor testing, it is better to avoid direct sunlight if the weather is cloudy, at night or sunny after sunset;

D) The radiation around the testing equipment is uniform, and the reflection interference caused by nearby heat radiation sources that can affect the measurement results should be avoided as far as possible;

E) No strong electromagnetic field around.

3. Infrare temperature measurment application case

In the process of infrared temperature measurement, when the measured temperature of a phase of an electrical equipment is higher than the normal value, the relative temperature difference is calculated according to DL/T664-2016 Infrared Diagnostic Application Specification for Charged Equipment to analyze whether the temperature difference between the phases of the equipment is within the normal range.
* Relative temperature difference: the percentage δ T of the ratio between the difference of temperature rise between the two corresponding measurement points and the temperature rise at the higher point, which can be obtained by the following formula:
For example, in a temperature measurement, the three phase temperatures are:
It can be seen that the temperature of phase B is significantly higher than that of phase A and PHASE C. The hot spot temperature of phase B is T1 =50.1℃. Take phase C as the corresponding point, and the temperature T2 =29.4℃ and the ambient temperature T0 =27.0℃.

δ= (50.1-29.4)/(50.1-27) *100%=89.6%

The defect level of the hot spot can be determined by combining the defect temperature value of the equipment and the defect diagnosis criterion table.

4. Conlusion

Today, the infrared thermal imaging technology has been widely used in electrical installation, testing, operation, and other fields, it can be in contact with electrical equipment, rapid, accurate, visually it is concluded that the running equipment surface temperature data, so as to help related personnel to more fully understand and evaluation of equipment installation, operation information such as the quality, Makes the troubleshooting of electrical equipment easy and convenient.