JP3380683B2 - Temperature drift correction device for infrared camera - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared camera which detects infrared rays emitted from an object and displays a thermal image showing a temperature distribution of the object. The present invention relates to a temperature drift correction device that can correct fluctuations in observation temperature due to temperature. 2. Description of the Related Art In recent years, an infrared camera which detects infrared rays emitted from an object and displays a thermal image has been used for various thermal analyses. In such an infrared camera, a signal obtained from the infrared sensor changes according to a change in ambient air temperature. Therefore, if a thermal image is formed as it is based on the signal output from the infrared sensor, a change in the outside air temperature is perceived as a change in the temperature of the object even when the object to be observed at a constant temperature is observed. Therefore, in a conventional infrared camera, a temperature sensor is provided in each of an optical system for guiding incident infrared rays to the infrared sensor and an outside air inlet for cooling, and the output of the infrared sensor is obtained based on temperature information of one or both of them. Was corrected. FIG. 4A is a diagram showing a structure of a conventional infrared camera, and FIG. 4B is a diagram showing a structure of an infrared sensor in the infrared camera. The infrared sensor 2 includes
A cooler 3 for cooling it is attached.
The cooler 3 cools the sensor 2 by an electronic cooling method using a Peltier element. The Peltier device has the advantages that the temperature response is fast, long life and high reliability can be expected. As is well known, a Peltier device has a low-temperature part where an endothermic phenomenon occurs and a high-temperature part where a heat generation phenomenon occurs.
The infrared sensor 2 is attached to the low temperature part, and the heat sink 4 is attached to the high temperature part in order to increase heat radiation efficiency. Then, outside air is introduced into the housing 13 by a fan 14 provided in the housing 13 of the infrared camera, and the wind hits the heat sink 4 to further increase the heat radiation efficiency. When the outside air temperature changes, an outside air temperature sensor 7 provided at the outside air intake of the infrared camera detects the change in the outside air temperature. Subsequently, due to a change in the outside air hitting the heat sink 4, the heat sink 4 was connected to the heat sink 4.
The temperature of the housing 5 covering the sensor 2 and the cooler 3 changes, and the radiant energy from the housing 5 causes the infrared sensor 2
Output changes. And the temperature inside the optical system 1 is
The optical system 1 changes gradually according to the fluctuation of the outside air temperature.
The optical system internal temperature sensor 12 that measures the internal temperature of the optical sensor detects the change in temperature at the latest among the above three sensors. [0006] As described above, in the conventional infrared camera, the fluctuation (temperature drift) of the observation temperature due to the outside air temperature is corrected by the outside air temperature sensor and the optical system internal temperature sensor. However, as described above, the output signal of the infrared sensor changes with a delay with respect to the change of the outside air temperature, so that the response of the outside air temperature sensor to the output fluctuation of the infrared sensor is too fast. Further, the response of the optical system internal temperature sensor to the output fluctuation of the infrared sensor is too slow. Therefore, in the conventional infrared camera, it is not possible to appropriately correct the output fluctuation of the infrared sensor, and there is a problem that a difference occurs between the measured temperature and the original temperature of the observed object. SUMMARY An advantage of some aspects of the invention is to provide a temperature drift correction device capable of accurately correcting a temperature drift with respect to a change in outside air temperature. A temperature drift correction device according to the present invention includes a variable gain amplifier for amplifying an output signal of an infrared sensor with a gain according to a gain control signal, and an outside air temperature for measuring an outside air temperature. Measuring means, averaging means for averaging the measured outside air temperature, and a temperature value output from the averaging means so that the temperature indicated by the output signal of the variable gain amplifying means matches the temperature of the object to be observed. And a gain control means for generating a gain control signal corresponding to. In this way, the averaging means obtains the average value of the outside air temperature measured by the outside air temperature measuring means, so that the temperature change corresponding to the output fluctuation of the infrared sensor due to the change of the outside air temperature, that is, the correction of the infrared sensor output. An appropriate temperature change can be artificially generated. Then, the gain control means generates a gain control signal corresponding to the temperature value output from the averaging means,
A signal whose temperature drift is corrected by increasing or decreasing the gain of the variable gain amplifier is output. FIG. 1 is a block diagram of an infrared camera showing a first embodiment of the present invention. Infrared light emitted from a not-shown object to be observed enters an infrared sensor 2 through an optical system 1. The optical system 1 includes an infrared transmission filter, and guides only infrared light of incident light to the infrared sensor 2. As a result, an output signal indicating the temperature of the observed object is output from the infrared sensor 2. The variable gain amplifier 6 amplifies the output of the infrared sensor 2 with a gain α described later. That is, assuming that the output value of the infrared sensor 2 is X, the output value Y of the variable gain amplifier 6 can be expressed by the following equation. Y = αX (1) An image processing unit (not shown) and a display device are connected behind the variable gain amplifier 6 so that the output of the variable gain amplifier 6 can be displayed on the display device by the image processing unit. As a result, the thermal image indicating the temperature distribution of the observed object is displayed on the display device. Next, the operation of temperature drift correction in such an infrared camera will be described. The basic structure of the infrared camera according to the present embodiment is the same as that shown in FIG. The outside air temperature sensor 7 provided at the outside air intake of the infrared camera measures the temperature of the outside air intake, and the A / D converter 8 A / D converts the output of the outside air temperature sensor 7. Next, the averaging circuit 9 calculates a moving average of the sampled values of the outside air temperature sensor 7 digitized by the A / D converter 8. FIG. 2 shows an averaging circuit 9.
FIG. The latch circuits 21 to 23 have an A / D
The input is held at the timing of the sampling clock of the converter 8. Therefore, the output Rd of the latch circuit 23 is a value three sampling clocks before the input Ra of the latch circuit 21 (the output of the A / D converter 8). The output Rc of the latch circuit 22 has a value two sampling clocks before the input Ra of the latch circuit 21, and the output Rb of the latch circuit 21 has a value one sampling clock before. Subsequently, the arithmetic circuit 24 uses the sample values Ra to Rd to calculate the output value A as in the following equation. A = (Ra + Rb + Rc + Rd) / D (2) Here, since the average of the four sample values Ra to Rd is taken, D = 4. The averaging circuit 9 calculates such an average value for each sampling clock. In this embodiment, the average of the four sample values is obtained. However, the average of the sample values is determined according to the output fluctuation of the infrared sensor 2. That is, the number of sample values is determined such that a temperature change corresponding to the output fluctuation of the sensor 2 accompanying the change in the outside air temperature is generated in a pseudo manner. Therefore, according to the determined number of sample values, the number of latch circuits and the expression (2)
Needless to say, the divisor D changes. Next, the CPU 10 stores a temperature-gain characteristic line in which a gain necessary for correcting a variation in the output signal of the infrared sensor 2 and an outside air temperature are stored in the form of a digital value table. I have. FIG. 3 shows an example of the temperature-gain characteristic line. Here, how to obtain the temperature-gain characteristic line will be described. First, the object to be observed is a black body furnace, and the temperature of the black body furnace is set to a constant value Tref. The output value of the outside air temperature sensor 7 is
An infrared camera is installed in an environment indicating the temperature TE1 of the above, and the black body furnace is observed. Since the outside air temperature is constant here,
The output of the A / D converter 8 and the output of the averaging circuit 9 have the same value. When observing a blackbody furnace with a constant temperature, the output signal Y output from the variable gain amplifier 6 must indicate the temperature Tref of the blackbody furnace. The gain α required to be equal to Tref (this is α1) can be obtained from the output value X of the infrared sensor 2 at this time. Subsequently, the output value of the outside air temperature sensor 7 is
An infrared camera is installed in an environment showing the temperature TE2 of the above, and the black body furnace is observed. Similarly to the above, the output signal Y output from the variable gain amplifier 6 must indicate the temperature Tref of the black body furnace, so that the gain α required for the output value Y to become equal to the temperature Tref (this is α2) Can be obtained from the output value X of the sensor 2 at this time. Thus, the temperature-gain characteristic line can be obtained. When the temperature-gain characteristic line has a curve as shown in FIG. 3, gains α may be similarly obtained for about three temperatures TE3 to TE5 to determine the temperature-gain characteristic line. . The relationship between the outside air temperature and the gain thus determined is stored in the form of a table in the CPU 10 in advance. Then, the CPU 10 reads the gain corresponding to the output value of the averaging circuit 9 from the table, and outputs the digital value of the gain control signal indicating the gain α to the D / A converter 11. The digital value of the gain control signal is D / A
By being converted into an analog signal by the conversion circuit 11, the variable gain amplifier 6 increases or decreases the gain according to the gain control signal. The temperature drift correction is performed as described above. Although the average value of the outside air temperature is obtained by the averaging circuit 9 in the present embodiment, a similar average value may be obtained by software processing of the CPU 10 without providing the averaging circuit 9. According to the present invention, the averaging means obtains the average value of the outside air temperature, whereby a temperature change corresponding to the output fluctuation of the infrared sensor accompanying the change of the outside air temperature is generated in a pseudo manner. Since the gain control means generates a gain control signal corresponding to the temperature value output from the averaging means, the gain of the variable gain amplifying means is increased or decreased.
A temperature drift due to a change in the outside air temperature can be accurately corrected, and an infrared camera that accurately represents the temperature of the observed object even when the outside air temperature changes can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an infrared camera showing a first embodiment of the present invention. FIG. 2 is a block diagram of the averaging circuit of FIG. 1; FIG. 3 is a characteristic diagram showing a relationship between an outside air temperature and a gain of a variable gain amplifier. FIG. 4 is a diagram showing the structure of a conventional infrared camera and infrared sensor. [Description of Signs] 1 ... optical system, 2 ... infrared sensor, 3 ... cooler, 4 ... heat sink, 5 ... casing, 6 ... variable gain amplifier, 7 ... outside air temperature sensor, 8 ... A / D converter, 9 ... Averaging circuit, 10 ... CPU, 11 ... D / A converter.

Claims (1)

(57) [Claims] 1. An infrared camera which receives infrared rays emitted from an object to be observed by an optical system, detects the infrared rays with an infrared sensor, and displays the temperature of the object to be observed. A temperature drift correction device for correcting fluctuations in observed temperature due to ambient outside air temperature, wherein the variable gain amplification means amplifies an output signal of the infrared sensor with a gain according to a gain control signal; , An averaging means for taking an average value of the measured outside air temperatures, and an averaging means such that the temperature indicated by the output signal of the variable gain amplifier means matches the temperature of the object to be observed. And a gain control means for generating the gain control signal according to the temperature value output from the infrared camera.