Calibration device and calibration method for infrared temperature sensor

Abstract

The invention provides a calibration device and method for an infrared temperature sensor, and the device comprises an adjustment platform, a constant-temperature water tank, a black body cavity, and a standard platinum resistance thermometer, and the adjustment platform is fixedly disposed above the constant-temperature water tank. The standard platinum resistance thermometer and the black body cavity are fixed at the bottom of the adjusting platform and extend into the constant-temperature water tank; the adjusting platform can bear and install the infrared temperature sensor to be measured and adjust the height of the infrared temperature sensor to be measured; a plurality of circles of gas pipes are wound on the outer surface of the blackbody cavity, supply gas to the gas pipes through gas cylinders, the gas flow rate in the gas pipes is adjusted through gas valves, the gas pipes are provided with transition sections immersed in the constant-temperature water tank, and the gas in the gas pipes passes through the transition sections and then is wound on the outer surface of the blackbody cavity after being discharged from the gas cylinders. The calibration device for the infrared temperature sensor provided by the invention is simple and convenient to use, and can reliably realize calibration of the infrared temperature sensor when the infrared temperature sensor is applied to a low-temperature scene.

Description

Technical Field

[0001] The invention relates to the technical field of temperature calibration of temperature measuring equipment, and in particular to a calibration device and a calibration method for an infrared temperature sensor. Background Art

[0002] The ocean surface skin temperature is one of the most important parameters at the interface between the ocean and the atmosphere. It plays a great role in environmental science, agriculture and fisheries, energy development and even the military. At present, satellite remote sensing is widely used at home and abroad to obtain a wide range of ocean surface skin temperature, but satellite remote sensing is greatly affected by the environment and cannot meet the 0.3K accuracy requirement stipulated by the World Climate Research Program Workshop. Therefore, it is necessary to use shipborne measurement data to correct satellite remote sensing measurement results. With the rapid development of science and technology, many ocean surface measurement equipment has emerged.

[0003] When performing non-contact seawater surface temperature measurement, an infrared temperature sensor is often required. Its working principle is to receive the infrared radiation signal emitted by the target and calculate the actual temperature of the target through the signal strength. The working scenario of the infrared sensor targeted by the calibration equipment in the prior art is often the temperature measurement above zero degrees Celsius. For example, the patent document with announcement number CN113358232A discloses an infrared body temperature calibration device with a dual-cavity blackbody radiation source, which is used to calibrate ear temperature and forehead temperature equipment; the calibration device is provided with a constant temperature bath and a blackbody tube, and the constant temperature bath is used to provide a temperature field to the blackbody tube for calibration.

[0004] In the measurement of seawater surface temperature, the working environment of the infrared temperature sensor may be zero degrees Celsius or below. The calibration equipment in the prior art does not have the ability to calibrate the infrared temperature sensor in low-temperature working scenarios. Summary of the invention

[0005] The embodiments of the present invention provide a calibration device and a calibration method for an infrared temperature sensor, so as to solve the problem that the calibration device in the prior art is not capable of calibrating the infrared temperature sensor in a low-temperature working scenario.

[0006] To achieve the above objectives, the embodiments of the present invention adopt the following technical solutions:

[0007] A calibration device for an infrared temperature sensor comprises an adjustment platform, a constant temperature water tank, a black body cavity and a standard platinum resistance thermometer, wherein the adjustment platform is fixedly installed above the constant temperature water tank, the black body cavity is fixed at the bottom of the adjustment platform and extends into the constant temperature water tank, and the standard platinum resistance thermometer is fixed at the bottom of the adjustment platform and extends into the constant temperature water tank;

[0008] The adjustment platform can carry and install the infrared temperature sensor to be measured and adjust the height of the infrared temperature sensor to be measured, so that the infrared temperature sensor to be measured extends into the black body cavity from top to bottom, and the temperature measuring end of the infrared temperature sensor to be measured faces downward;

[0009] There are multiple turns of air pipes wrapped around the outer surface of the black body cavity. The air pipes continuously supply gas through the gas cylinder outside the constant temperature water tank. The outlet of the gas cylinder is provided with an air valve for adjusting the gas flow rate in the air pipe. The air pipe has a transition section immersed in the constant temperature water tank. After the gas in the air pipe is leaked from the gas cylinder, it first passes through the transition section to make the gas temperature in the air pipe consistent with the liquid temperature in the constant temperature water tank, and then is wrapped around the outer surface of the black body cavity.

[0010] Furthermore, the blackbody cavity comprises a hollow cylindrical section and a conical section at the bottom.

[0011] Furthermore, the black body cavity is formed by processing red copper.

[0012] Furthermore, the inner surface of the black body cavity is coated with graphite infrared auxiliary coating, so that the emissivity of the black body cavity is greater than 0.998.

[0013] Furthermore, the outer surface of the black body cavity is plated with gold.

[0014] Furthermore, the adjustment platform is fixedly mounted on the test bench, a constant temperature water tank is formed on the test bench, the adjustment platform includes a base, a lifting frame and a clamp, the base is fixedly mounted on the constant temperature water tank, and the black body cavity and the standard platinum resistance thermometer are both fixed to the bottom of the base;

[0015] The lifting frame is fixedly installed on the base, the clamp is installed on the lifting frame and can be driven by the lifting frame to move longitudinally, and the clamp is used to clamp the infrared temperature sensor to be measured.

[0016] A calibration method for an infrared temperature sensor, the calibration method is based on the aforementioned calibration device for an infrared temperature sensor, the calibration method for an infrared temperature sensor comprises the following steps:

[0017] S1. Place the infrared temperature sensor to be tested on the adjustment platform, aim the temperature measuring end of the infrared temperature sensor to be tested at the center of the black body cavity, and adjust the height of the infrared temperature sensor to be tested so that the temperature measuring end of the infrared temperature sensor to be tested is flush with the upper opening of the black body cavity, and the bottom of the standard platinum resistance thermometer and the cone tip at the bottom of the black body cavity are in the same horizontal plane.

[0018] S2. Select -5℃, 0℃, 10℃, 20℃, 30℃, and 40℃ as temperature test points, adjust the temperature in the constant temperature water bath, and test from high to low temperatures; before adjusting the temperature of the constant temperature water bath, first plug the black body cavity with a rubber plug, then adjust the temperature, and monitor the temperature in the constant temperature water bath with a standard platinum resistance thermometer. When the temperature in the constant temperature water bath reaches and stabilizes at the temperature test point, remove the rubber plug for calibration; during the cooling process, keep the air pipe ventilated and adjust the gas flow rate in the air pipe so that the temperature in the constant temperature water bath can remain stable at the temperature test point.

[0019] S3. When the infrared temperature sensor to be tested is measuring temperature, it is necessary to wait for the indication of the infrared temperature sensor to be tested to stabilize before reading the value, and the waiting time should be at least three times the response time of the indication change of the infrared temperature sensor to be tested, and read the indication of the standard platinum resistance thermometer and the indication of the infrared temperature sensor to be tested.

[0020] S4. Repeat steps S2-S3 10 times. For each temperature test point, the calculation formula of the indication error Δt is: Δt=t-(t1+Δt1), where t1 is the indication of the standard platinum resistance thermometer, and Δt1 is the correction value quoted when the actual emissivity of the black body cavity deviates from 1. For each temperature test point, take the average of the indication error Δt obtained by 10 measurements to obtain the average indication error of each temperature test point, and then calibrate according to the calibration formula of the infrared temperature sensor when it leaves the factory.

[0021] Furthermore, the calibration method for the infrared temperature sensor also includes a pre-step that needs to be performed before placing the infrared temperature sensor to be measured on the adjustment platform, and the pre-step includes:

[0022] S1. Control the temperature and humidity of the laboratory at 20-23 degrees Celsius and 20-70% RH.

[0023] S2. Clean the lens of the sensor and set the emissivity setting value of the infrared temperature sensor to be tested to 1. If the emissivity value of the infrared temperature sensor to be tested is not 1, it needs to be corrected. In addition, the lens of the sensor needs to be cleaned before the experiment.

[0024] S3. Place the infrared temperature sensor to be tested in an experimental environment with controlled temperature and humidity for more than 3 hours. When the initial temperature is significantly different from the laboratory environment, the placement time should be extended so that the temperature of the infrared temperature sensor to be tested is consistent with the ambient temperature.

[0025] The beneficial effects of the present invention are:

[0026] The calibration device for an infrared temperature sensor provided by the present invention is easy to use and can reliably realize the calibration of the infrared temperature sensor when it is applied in a low-temperature scene. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A stereogram for adjusting the platform;

[0028] Figure 2 is a perspective view of a calibration device for an infrared temperature sensor;

[0029] Figure 3 is a top view of a calibration device for an infrared temperature sensor;

[0030] Figure 4 for Figure 3 Sectional view of section AA;

[0031] Figure 5 is a schematic diagram of the working state of a calibration device for an infrared temperature sensor;

[0032] Figure 6 Schematic diagram of the calibration experiment of the infrared temperature sensor.

[0033] Description of reference numerals:

[0034] 1. Adjustment platform; 11. Base; 12. Lifting frame; 13. Clamp; 2. Black body cavity; 3. Infrared temperature sensor to be tested; 4. Test bench; 41. Constant temperature water tank; 5. Standard platinum resistance thermometer; 6. Gas pipe; 61. Gas cylinder; 62. Gas valve; 7. Thermometer; 71. Computer; 8. Experimental water tank; 81. Adjustable bracket; 82. Inclinometer; 83. Shielding cover; 9. Contact temperature sensor. DETAILED DESCRIPTION

[0035] The specific implementation of the present application is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present application, and is not used to limit the present application.

[0036] like Figure 1-5 As shown, an embodiment of the present invention provides a calibration device for an infrared temperature sensor, which specifically includes an adjustment platform 1, a constant temperature water tank 41, a black body cavity 2 and a standard platinum resistance thermometer 5. The adjustment platform 1 is fixedly installed above the constant temperature water tank 41, the black body cavity 2 is fixed to the bottom of the adjustment platform 1 and extends into the constant temperature water tank 41, and the standard platinum resistance thermometer 5 is fixed to the bottom of the adjustment platform 1 and extends into the constant temperature water tank 41; the adjustment platform 1 can carry and install the infrared temperature sensor 3 to be measured and adjust the height of the infrared temperature sensor 3 to be measured, so that the infrared temperature sensor 3 to be measured extends from top to bottom into the black body cavity 2, and the temperature measuring end of the infrared temperature sensor 3 to be measured faces downward.

[0037] As a major improvement of the present invention, considering that condensation may occur on the outer surface of the blackbody cavity 2 during low-temperature calibration, thereby affecting the experiment, in a preferred embodiment, a plurality of turns of air pipe 6 are wrapped around the outer surface of the blackbody cavity 2, and the air pipe 6 is supplied with gas through a gas cylinder 61 outside the constant-temperature water tank 41, and an air valve 62 for adjusting the air flow rate in the air pipe 6 is provided at the outlet of the gas cylinder 61; in order to reduce the temperature influence brought by the external gas introduced into the air pipe 6, the air pipe 6 has a transition section immersed in the constant-temperature water tank 41, and after the gas in the air pipe 6 leaks out from the gas cylinder 61, it first passes through the transition section to make the gas temperature in the air pipe 6 consistent with the liquid temperature in the constant-temperature water tank 41, and then is wrapped around the outer surface of the blackbody cavity 2.

[0038] In a preferred embodiment, the black body cavity 2 includes a hollow cylindrical section and a conical section at the bottom, and is formed by copper processing. The inner surface of the black body cavity 2 is coated with graphite infrared auxiliary coating so that the emissivity of the black body cavity 2 is greater than 0.998. The outer surface of the black body cavity 2 is gold-plated to prevent oxidation of the outer surface of the black body cavity 2.

[0039] In such Figure 1-4 In the specific embodiment shown, the adjustment platform 1 is fixedly mounted on the test bench 4, a constant temperature water tank 41 is formed on the test bench 4, the adjustment platform 1 includes a base 11, a lifting frame 12 and a clamp 13, the base 11 is fixedly mounted on the constant temperature water tank 41, the aforementioned black body cavity 2 and the standard platinum resistance thermometer 5 are both fixed to the bottom of the base 11; the lifting frame 12 is fixedly mounted on the base 11, the clamp 13 is mounted on the lifting frame 12 and can be driven by the lifting frame 12 to move longitudinally, and the clamp 13 is used to clamp the infrared temperature sensor 3 to be measured.

[0040] like Figure 5 As shown, in a specific calibration work, the standard platinum resistance thermometer 5 is connected to an external thermometer 7, and the thermometer 7 collects temperature data and transmits the data to a computer 71, which performs statistical analysis.

[0041] The present invention also provides a calibration method based on the calibration device of the infrared temperature sensor:

[0042] S1. Control the temperature and humidity of the laboratory at 20-23 degrees Celsius and 20-70% RH.

[0043] S2. Clean the lens of the sensor, set the emissivity setting value of the infrared temperature sensor 3 to be tested to 1. If the emissivity value of the infrared temperature sensor 3 to be tested is not 1, it needs to be corrected. In addition, the lens of the sensor needs to be cleaned before the experiment.

[0044] S3. Place the infrared temperature sensor 3 to be tested in an experimental environment with controlled temperature and humidity for more than 3 hours. When the initial temperature is significantly different from the laboratory environment, the placement time should be extended so that the temperature of the infrared temperature sensor 3 to be tested should be consistent with the ambient temperature.

[0045] S4. Place the infrared temperature sensor 3 to be measured on the adjustment platform 1, aim the temperature measuring end of the infrared temperature sensor 3 to be measured at the center of the black body cavity, and adjust the height of the infrared temperature sensor 3 to be measured so that the temperature measuring end of the infrared temperature sensor 3 to be measured is flush with the opening position of the upper part of the black body cavity 2, so that the bottom of the standard platinum resistance thermometer 5 and the cone tip at the bottom of the black body cavity 2 are in the same horizontal plane.

[0046] S5. Select -5°C, 0°C, 10°C, 20°C, 30°C, and 40°C as temperature test points, adjust the temperature in the constant temperature water tank 41, and test from high to low temperatures; before adjusting the temperature of the constant temperature water tank 41, first plug the black body cavity with a rubber plug, then adjust the temperature, and monitor the temperature in the constant temperature water tank 41 through a standard platinum resistance thermometer 5. When the temperature in the constant temperature water tank 41 reaches and stabilizes at the temperature test point, remove the rubber plug for calibration; during the cooling process, keep the trachea ventilated, and adjust the gas flow rate in the trachea so that the temperature in the constant temperature water tank 41 can remain stable at the temperature test point.

[0047] S6. When the infrared temperature sensor 3 to be measured is measuring temperature, it is necessary to wait for the indication of the infrared temperature sensor 3 to be measured to stabilize before reading the value, and the waiting time is at least three times the indication change response time of the infrared temperature sensor 3 to be measured (for example, if the indication change response time of the infrared temperature sensor 3 to be measured is 0.6S, then wait at least 1.8S before reading the value), read the indication of the standard platinum resistance thermometer 5 and the indication of the infrared temperature sensor 3 to be measured.

[0048] S7. Repeat steps S5-S6 in a loop and perform 10 measurements. For each temperature test point, the calculation formula of the indication error Δt is: Δt=t-(t1+Δt1), where t1 is the indication of the standard platinum resistance thermometer 5, and Δt1 is the correction value quoted when the actual emissivity of the black body cavity deviates from 1. For each temperature test point, take the average value of the indication error Δt obtained by 10 measurements to obtain the average indication error of each temperature test point, and then calibrate according to the calibration formula of the infrared temperature sensor 3 when it leaves the factory (the infrared temperature sensors used in the prior art cover a variety of brands and specifications, and the corresponding calibration formulas of different infrared temperature sensors are inconsistent when they leave the factory, so they are not listed in detail here).

[0049] In the above calibration method, steps s1-s3 are pre-steps for reducing the impact of environmental factors, and steps s4-s7 are formal calibration operation steps.

[0050] Since the blackbody cavity is a standard heat source that can provide a specific temperature, the blackbody radiation source cannot fully simulate the actual sea surface conditions for the sea surface temperature thermometer, a precision device for measuring the sea surface. After the infrared temperature sensor is calibrated, in order to further calibrate the calibrated infrared temperature sensor, such as Figure 6 As shown, it is also necessary to conduct the ocean skin temperature comparison test in a constant temperature and humidity laboratory. Therefore, an experimental water tank 8 is used to contain seawater and the seawater in the experimental water tank 8 is controlled to be constant temperature (the laboratory fluctuation uniformity is 0.005°C) to replace the black body to provide standard temperature; the infrared temperature sensor 3 to be tested is fixedly installed on the edge of the experimental water tank through an adjustable bracket 81, and the infrared temperature sensor 3 to be tested can adjust its own inclination angle with the help of the adjustable bracket 81, as well as the height of the infrared temperature sensor 3 to be tested relative to the water surface in the experimental water tank 8. At the same time, an inclinometer is also set on the infrared temperature sensor 3 to be tested to observe the inclination angle of the infrared temperature sensor 3 to be tested.

[0051] Since infrared temperature measurement may be interfered by atmospheric radiation, a shielding cover 83 is also provided on the outer edge of the measuring end of the infrared temperature sensor 3 to be measured (the size of the shielding cover needs to be designed taking into account the field of view and distance of the device being used). The temperature change of the water tank is adjusted, and the measurement result of the contact temperature sensor 9 is used as the standard value (standard platinum resistance thermometer or existing high-precision contact epidermis meter) to compare the true value and evaluate whether the infrared temperature sensor 3 to be measured has been calibrated.

[0052] In addition, since the calm water surface cannot reflect the actual measurement of the seawater surface temperature, there is a temperature difference between the skin layer temperature on the water surface and the lower water temperature. A stirrer is also installed in the experimental water tank 8. The stirrer is used to mix the various layers of the water body evenly, eliminate the gradient differences between the various layers of the water body, and reduce errors.

[0053] The calibration device for infrared temperature sensors provided by the present invention provides a uniform temperature field for the black body cavity by immersing the black body cavity in a constant temperature water tank, and the black body cavity is made of a material with high thermal conductivity so that the liquid temperature can be approximately equal to the temperature of the black body radiation cavity, providing a standard temperature value for the infrared temperature sensor to be tested, and preventing condensation in the black body cavity at low temperatures by winding an air tube around the outside of the black body cavity and ventilating the cavity. The calibration device provided by the present invention is easy to use and can reliably realize the calibration of infrared temperature sensors when applied to low temperature scenes.

[0054] The above-described embodiments only express the implementation methods of the present invention, but they cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A calibration device for an infrared temperature sensor, characterized in that: The apparatus comprises an adjusting platform (1), a constant temperature water tank (41), a black body cavity (2) and a standard platinum resistance thermometer (5), wherein the adjusting platform (1) is fixedly mounted above the constant temperature water tank (41), the black body cavity (2) is fixedly mounted at the bottom of the adjusting platform (1) and extends into the constant temperature water tank (41), and the standard platinum resistance thermometer (5) is fixedly mounted at the bottom of the adjusting platform (1) and extends into the constant temperature water tank (41); The adjustment platform (1) is capable of carrying and installing the infrared temperature sensor (3) to be measured and adjusting the height of the infrared temperature sensor (3) to be measured, so that the infrared temperature sensor (3) to be measured extends from top to bottom into the black body cavity (2), and the temperature measuring end of the infrared temperature sensor (3) to be measured faces downward; The outer surface of the black body cavity (2) is wound with a plurality of turns of an air pipe (6), the air pipe (6) continuously supplies air through a gas cylinder (61) outside a constant temperature water tank (41), an air valve for adjusting the flow rate of the gas in the air pipe (6) is arranged at the outlet of the gas cylinder (61), the air pipe (6) has a transition section immersed in the constant temperature water tank (41), after the gas in the air pipe (6) is discharged from the gas cylinder (61), it first passes through the transition section so that the temperature of the gas in the air pipe (6) is consistent with the temperature of the liquid in the constant temperature water tank (41), and then is wound around the outer surface of the black body cavity (2).

2. The calibration device for infrared temperature sensor according to claim 1, characterized in that: The black body cavity (2) comprises a hollow cylindrical section and a conical section at the bottom.

3. The calibration device for infrared temperature sensor according to claim 2, characterized in that: The black body cavity (2) is formed by processing red copper.

4. The calibration device for infrared temperature sensor according to claim 2, characterized in that: The inner surface of the black body cavity (2) is coated with graphite infrared auxiliary coating, so that the emissivity of the black body cavity (2) is greater than 0.

998.

5. The calibration device for infrared temperature sensor according to claim 2, characterized in that: The outer surface of the black body cavity (2) is plated with gold.

6. The calibration device for infrared temperature sensor according to claim 1, characterized in that: The adjustment platform (1) is fixedly mounted on the test bench (4), a constant temperature water tank (41) is formed on the test bench (4), the adjustment platform (1) comprises a base (11), a lifting frame (12) and a clamp (13), the base (11) is fixedly mounted on the constant temperature water tank (41), and the black body cavity (2) and the standard platinum resistance thermometer (5) are both fixed to the bottom of the base (11); The lifting frame (12) is fixedly mounted on the base (11), the clamp (13) is mounted on the lifting frame (12) and can be driven by the lifting frame (12) to move longitudinally, and the clamp (13) is used to clamp the infrared temperature sensor (3) to be measured.

7. A calibration method for an infrared temperature sensor, characterized in that: The calibration method is based on the calibration device for an infrared temperature sensor according to any one of claims 1 to 6, and the calibration method for an infrared temperature sensor comprises the following steps: S1. Place the infrared temperature sensor (3) to be measured on the adjustment platform (1), aim the temperature measuring end of the infrared temperature sensor (3) to be measured at the center of the black body cavity, and adjust the height of the infrared temperature sensor (3) to be measured so that the temperature measuring end of the infrared temperature sensor (3) to be measured is flush with the opening position of the upper part of the black body cavity (2), so that the bottom of the standard platinum resistance thermometer (5) and the cone tip at the bottom of the black body cavity (2) are in the same horizontal plane. S2. Select -5°C, 0°C, 10°C, 20°C, 30°C, and 40°C as temperature test points, adjust the temperature in the constant temperature water tank (41), and test from high to low temperatures; before adjusting the temperature of the constant temperature water tank (41), first block the black body cavity with a rubber plug, then adjust the temperature, and monitor the temperature in the constant temperature water tank (41) through a standard platinum resistance thermometer (5). When the temperature in the constant temperature water tank (41) reaches and stabilizes at the temperature test point, remove the rubber plug for calibration; during the cooling process, keep the air pipe ventilated, and adjust the gas flow rate in the air pipe so that the temperature in the constant temperature water tank (41) can remain stable at the temperature test point. S3. When the infrared temperature sensor (3) to be measured is used for temperature measurement, it is necessary to wait for the indication of the infrared temperature sensor (3) to be measured to stabilize before reading the value, and the waiting time is at least three times the response time of the indication change of the infrared temperature sensor (3) to be measured, and read the indication of the standard platinum resistance thermometer (5) and the indication of the infrared temperature sensor (3) to be measured. S4. Repeat steps S2-S3 10 times. For each temperature test point, the calculation formula of the indication error Δt is: Δt = t-(t1 + Δt1), where t1 is the indication of the standard platinum resistance thermometer (5), and Δt1 is the correction value quoted when the actual emissivity of the black body cavity deviates from 1. For each temperature test point, the indication error Δt obtained by the 10 measurements is averaged to obtain the average indication error of each temperature test point, and then calibrated according to the calibration formula of the infrared temperature sensor (3) when it leaves the factory.

8. The calibration method for an infrared temperature sensor according to claim 7, characterized in that: The infrared temperature sensor calibration method further comprises a pre-step that needs to be performed before placing the infrared temperature sensor (3) to be measured on the adjustment platform (1), and the pre-step comprises: S1. Control the temperature and humidity of the laboratory at 20-23 degrees Celsius and 20-70% RH. S2. Clean the lens of the sensor and set the emissivity setting value of the infrared temperature sensor (3) to be tested to (1). If the emissivity value of the infrared temperature sensor (3) to be tested is not (1), it needs to be corrected. In addition, the lens of the sensor needs to be cleaned before the experiment. S3. Place the infrared temperature sensor (3) to be tested in an experimental environment with controlled temperature and humidity for more than 3 hours. When the initial temperature is significantly different from the laboratory environment, the placement time should be extended so that the temperature of the infrared temperature sensor (3) to be tested is consistent with the ambient temperature.

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