JPH0295223A - Overheating detector - Google Patents

Abstract

PURPOSE:To detect temperature while reducing the influence of the sunshine by using two IRs (Infra Red) CCD, and picking up images in two different wavelength ranges. CONSTITUTION:An image pickup device consists of a convergence optical system 3, a split optical system 4 composed of a dichroic mirror 4-a and a band-pass filter 4-b, 1st and 2nd IR CCDs 5 and 6, a CCD driving circuit 7, an amplifier 8, a gain adjusting amplifier 9, and a differential amplifier 10. Radiation from a body 1 to be measured is converted by the convergence optical system 3 to form images on the IR CCDs 5 and 6. The radiation consists of heat radiation due to the temperature of the body 1 to be measured itself and the reflection of the sunshine 2. Then a signal from which the influence of the sunshine 2 is removed is obtained by subtracting the signal obtained by multiplying the output of the IR CCD 6 by a constant rate from the output of the IR CCD 5.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a technique for remotely measuring the temperature of an object using infrared imaging, and in particular, a technique for measuring temperature while removing the influence of sunlight to prevent overheating of the object to be measured. The present invention relates to an overheat detection device for detecting overheating.

[Conventional technology]

Conventionally, in this type of infrared imaging, either the 3-5 μm band or the 8-12 μm band, which is called the atmospheric window, is used. In the former 3 to 5 μm band, the influence of sunlight is large, causing a non-negligible error during daytime clear weather. Currently 8-12
This is also one of the reasons why the μm band is becoming mainstream.

However, in recent years, an imaging device has been developed as an IR (Infra Red) CCD that is sensitive in the 3 to 4 μm band and has a resolution and frame number comparable to that of a TV, and real-time imaging in this wavelength range is becoming easier.

[Problem to be solved by the invention]

When measuring the temperature of an object using infrared imaging, especially for detecting overheating of power transmission and distribution equipment, the measurement is limited to daytime, so reducing the influence of sunlight is of great practical importance. On the other hand, Pt1S i IRCCDs (platinum-silicide type IRCCDs), which are currently being put into practical use, have strong sensitivity on the short wavelength side and are therefore susceptible to this effect. For this reason, it is necessary to optically cut off the short wavelength side as much as possible in order to remove sunlight, but such measures also reduce the signal light itself and completely eliminate the influence of sunlight. Removal is difficult.

[Means to solve the problem]

According to the present invention, two IRCCDs are used to capture images in two different wavelength ranges, thereby providing means for realizing sunlight removal. That is, the intensity of sunlight is estimated and removed based on the imaging results from the IRCCD in two wavelength ranges, assuming the radiation spectrum of two signal lights of sunlight.

〔Example〕

Next, one embodiment of the present invention will be described with reference to FIG.

In Fig. 1, 1 is the object to be measured, 2 is the sunlight, 3 is the condensing optical system of the infrared imaging device, 4 is the optical system that splits the luminous flux into two wavelength ranges, 4-a gicchroic mirror, 4- It consists of a b-band pass filter. 5゜6 is two 17) IRCCD
, 7 is a CCD driving circuit, 8 is an amplifier, 9 is a gain adjustment amplifier, and 10 is a differential amplifier.

The IRCCD, which is an imaging device, has the spectral sensitivity characteristics shown in FIG. 2(a). On the other hand, the spectrum of sunlight is 59
It can be expressed by adding the atmospheric transmission characteristics to the blackbody radiation at 00 K, and a typical example of the spectrum is shown by the solid line in FIG. 2(b). At the same time, the dashed line in FIG. 2(b) shows the radiation spectrum of a room-temperature object.

Radiation from the object to be measured 1 is focused by a focusing optical system 3,
The image is formed on the IRCCD. The radiation consists of thermal radiation due to the temperature of the object itself and reflection of sunlight. It is assumed that the wavelength division optical system of FIG. 2 (c) is divided so that the broken line in FIG.

To simplify, the wavelength used for the first COD is λ2~λ2, and the wavelength used for the second COD is
The wavelengths used for COD are assumed to be λ1 to λ2. If the output signals of the first and second CODs are respectively V and V2, it can be expressed as follows. However, R1 is the spectral sensitivity characteristic (V/W, p m
) Bλ is the sunlight spectrum (W/μm) S is the thermal radiation spectrum (W/μm). Here, (a) in FIG. 2 corresponds to Rλ, a solid line in (b) corresponds to Bλ, and a broken line in (b) corresponds to SA. More required here. Here, in order to remove sunlight with less error, it is desirable that 〆 be as large as possible and b as small as possible. That is, a>b
(6) Therefore, equation (6) becomes a determination requirement for the intermediate wavelength λ2.

Naturally, in order to increase a in equation (6), the longer the wavelength of λ2 is, the better, and conversely, in order to decrease b, the shorter the wavelength, the better.

In order to improve measurement accuracy, it is necessary to perform measurements with as good a signal-to-noise ratio as possible. Therefore, equation (5) can be directly measured. This is based on equation (5).

The true signal component is equivalent to maximizing the value that should be proportional to the second term of equation (1). As an example, using the spectrum shown in FIG. 2, it can be calculated that the optimum λ2 is 32 μm.

In other words, the signal from which the influence of sunlight has been removed is transmitted to the first CCD.
It is obtained by subtracting (second CCD 6 output x -) from 5 output.

As explained above, in the present invention, one IRCC
The present invention provides a technique for appropriately solving the conflicting issues of removing sunlight and reducing signal light by cutting off the short wavelength side as much as possible using an optical filter.

Note that in this method, the output of the second IRCCD is multiplied by a certain ratio, and determining the ratio is important. This ratio is obtained by calculation assuming a spectrum. By using a reflector with a surface condition that is considered to be closest to that of the object to be measured, and by experimentally fine-tuning the ratio based on the indication scale when it is directly exposed to the sun and when it is not directly exposed to the sun,
It is considered that this method can also deal with actual spectral fluctuations.

〔Effect of the invention〕

As explained above, according to the present invention, there are two
By using the , it is possible to significantly reduce the influence of sunlight and check the temperature by capturing images in two wavelength ranges.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention. l...Object to be measured, 2...Sunlight, 3.
...Condensing optical system, 4...Dividing optical system, 5
...First IRCCD, 6... Second IRCCD, 7... CCD drive circuit, 8...
...Amplifier, 9...Gain adjustment amplifier, 10.
...Differential amplifier, Figure 2 shows the spectral characteristics of each part, and (a) shows the IRC.
Spectral high sensitivity characteristics of GfD, (b) emission spectrum, (
C) shows the split spectrum. Agent Patent Attorney Susumu Uchihara

Claims (1)

[Claims] In an overheating detection device that measures the surface temperature of an object using infrared imaging and detects overheated parts, two imaging devices using different wavelengths are used to simultaneously image the object, and the infrared image from the first imaging device is used to detect the object. When determining the temperature pattern, the infrared image result from the second image sensor on the shorter wavelength side is multiplied by a certain ratio and subtracted from the infrared image from the first image sensor to eliminate the influence of sunlight. An overheat detection device characterized by reducing overheating.