JPS6017072B2 - red hot metal detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a red-hot metal detector that detects the presence or absence of a metal body by using reflected light emitted from a metal body heated to a high temperature.

A conventional device of this type is shown in FIG.

In the figure, 1 is the object to be detected (red-hot metal), 2 is the neck radiation from the object to be detected, 3 is the detection field of view, 4 is the condenser lens that collects the neck radiation 2, 5 is the rotary slit plate for the chopper, and 6 is the rotary slit plate for the chopper. 7 is an AC intensifier, 8 is a DC converter, 9 is an AC intensifier, and 10 is an output relay.

Next, the operation will be explained.

When the solar radiation 2 emitted from the object 1 moving in the direction of the arrow 11 enters the detection field of view 3, the radiation 2 is condensed by the condensing lens 4 and transmitted to the photoelectric generator via the rotary slit plate 5 for the chopper. The light enters the light receiving surface of the converter 6. Photoelectric converter 6
generates an electrical signal proportional to the energy intensity of the input light. Therefore, theoretically, when the detected object 1 enters the detection field of view, in other words, at the moment when the scale light 2 crosses the detection field of view 3, the photoelectric converter 6 outputs an electrical signal proportional to the light intensity. be done. This signal changes as the detected object 1 moves, and shows a continuous output distribution as shown in FIG. Therefore, if the AC intensifier 7 sufficiently increases the power, converts it to a DC signal, and compares it with the DC reference level 22 in the comparison intensifier 9, when the tip of the detected object 1 enters the set reference level. , and when the tail end of the detected object 1 leaves the set reference position, a trigger action occurs at the trigger point 21 to generate an electrical 1,0 signal. Then, if the output relay 10 is turned on or off using this signal,
This means that the presence or absence of a metal object can be detected. However, in reality, when the temperature of the object to be detected passing through the detection field of view 3 ranges over a wide range, there are the following drawbacks.

As shown in FIG. 3a, the detection field 3 is
1 passes through, the output voltage of the photoelectric converter 6 is shown in Fig. 3c.
It is indicated by the reference numeral 26. Further, as shown in FIG. 3b, the output voltage when a high-temperature metal body lh passes is indicated by reference numeral 26 in FIG. 3c. The output voltage on the vertical axis of FIG. 3c is expressed on a logarithmic scale. The output voltage of the photoelectric converter 6 due to the eel radiation emitted by an object is approximately proportional to, for example, the fourth power of the temperature of the object, if saturation is not considered (the relationship between temperature and output voltage is more complicated, and here (The 4th power shown in Figure 4 only shows the approximate relationship), the output voltage ratio between the low temperature metal body 11 and the high temperature metal body lh may be a large value exceeding about 10". In general, the body 1
The reflectance of the reflector that exists within the range of movement is
If the Korean radiation from the high-temperature metal object lh that is not within the detection field of view 3 is diffusely reflected by the reflector 24 and reduced to 10% as shown in Figure 3b, then it will be reduced to 10%. It may be almost the same or larger than the direct radiation from the metal body 11. Therefore, in the apparatus shown in FIG. 1, it is not possible to distinguish whether the Korean radiation is directly from the low-temperature metal body 11 or whether the Korean radiation from the high-temperature metal body is diffusely reflected by another object. Thus, the detection operation is performed even though the high-temperature metal body lh does not enter the detection field of view 3. This invention was made to eliminate the above-mentioned drawbacks of conventional detectors, and it uses two infrared bandpass filters that transmit only light of different specific wavelengths to detect the difference between the two. By doing this, the difference in key radiation energy caused by temperature differences can be reduced to a large extent, and it is possible to know when the tip or tail of the object to be detected has actually reached the set reference position within the detection field of view. The present invention aims to provide a red-hot metal detector that can perform the following steps.

Embodiments of the present invention will be described below with reference to a block diagram showing an embodiment of a red-hot metal detector.

In the figure, numerals 1 to 5 and 8 to 11 are the same as the respective parts of the subordinate detector described in FIG. 6a and 6b are the first
and second photoelectric converters, 12a and 12b are respectively
and a second infrared bandpass filter, 13 a semi-transmissive mirror, and 14 a differential amplifier.

After the same operations as in the conventional device are performed according to numbers 1 to 5 in FIG. 4, the neck light 2 is separated into two optical paths by a semi-transmissive mirror 13, and two infrared bandpasses each having a different center wavelength are separated. The light enters the light receiving surfaces of the respective photoelectric converters 6a and 6b through the filters 12a and 12b. If we pay attention to FIG. 5a, in the distribution of the radiation energy from an ideal black body, as the temperature increases, the occupied zone becomes wider, and therefore the amount of radiation energy also increases.

Furthermore, the maximum sensitivity wavelength (the wavelength showing the maximum split radiance)
is shifted toward shorter wavelengths. That is, as shown in FIG. 5b, whereas conventionally the photoelectric converter 6 collects light in the entire sensitivity range of the photoelectric converter 6, two infrared bandpass filters 12a and 12b collect the light. If only the narrow bands of light of , , and 2 are targeted, the fin radiation energy ratio at the highest and lowest temperatures, that is, the output voltage ratio of the photoelectric converter, can be significantly reduced.

For example, if a PBS photoconductive cell is selected as the photoelectric converter 6, its sensitivity wavelength range is approximately 0.8 microns to 2.0 microns.
5 microns, and if the temperature range of the object to be detected is a normal red-hot metal body, then as mentioned above, the entire wavelength range (^: 0.8
When the target is light with a temperature of 2.5 m to 2.5 m, the output voltage ratio from the photoelectric converter at the highest and lowest temperatures will be approximately a three-digit value, if saturation is not considered. In general, the reflectance of a reflector existing within the range of movement of the detected object is approximately 10%, and the output voltage ratio (
3-digit numerical value), other objects (
This made it difficult to distinguish the diffused reflection from the reflector (reflector), causing malfunctions.

However, for example, two infrared bandpass filters 12
The center wavelengths of a and 12b are each 4.3 microns (^
2), 2.5 microns (^,), input the output voltage from each photoelectric converter 6a, 6b to the differential amplifier 14, and take the difference between them, the photoelectric converter at the highest and lowest temperature can be obtained. As shown in Figure 5c, the output power ratio from the converter can be reduced to approximately a single-digit value, and detection errors can be reduced even if there is a reflector with a reflectance of zero to several tens of percent. This can be prevented from occurring.

From the above, if the center wavelengths of the two infrared bandpass filters are selected according to the site environment (reflectance of the reflector), error factors can be completely eliminated.

In practice, considering the sensitivity range of the photoelectric converter, the center wavelengths of the two infrared bandpass filters are selected from 0.8 microns to 30 microns. Spectral transmittance of filter,
By changing the half value, etc., it is possible to bring the output voltage ratio closer to 1.

However, as shown in Figure 5c, there is a point (symbol p in the figure) where the differential output voltage of the two photoelectric converters becomes zero, so that point is not included within the temperature range of the detected object. It is necessary to select the center wavelength, spectral transmittance, half value, etc. of the two infrared bandpass filters 12a and 12b.

In this way, two infrared bandpass filters 12a, 1
2b and the differential intensifier 14 to sufficiently reduce the difference in reflected energy caused by the difference in temperature.
10, the same operation as before is performed. In the above embodiment, two infrared bandpass filters having different center wavelengths are used, but the photoelectric conversion is sensitive only to a narrow range of infrared wavelengths corresponding to the center wavelengths. You may use a container.

As described above, according to the present invention, by using two infrared bandpass filters having different center wavelengths and determining the differential output of each optical crab converter, fins caused by temperature differences can be reduced. The difference in radiation energy can be reduced to a large extent, and errors caused by, for example, diffused reflection from other objects due to fin radiation from a high-temperature metal body can be eliminated, leading to a medium-sized improvement in accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a red-hot metal detector from a secondary structure, FIGS. 2 and 3 are explanatory diagrams for explaining the operation of the conventional red-hot metal detector mentioned above, 4
The figure is a block diagram showing a red-hot metal detector according to the present invention, and FIG. 5 is an explanatory diagram for explaining the operation of the red-hot metal detector according to the present invention.

In the figure, 1 is the object to be detected, 2 is the light emitted from the object to be detected, 3 is the detection field of view, 4 is the condensing lens, 5 is the rotary slit plate for the chopper, and 6a and 6b are the first and second photoelectric converters. , 8 is a DC converter, 9 is a comparator amplifier, 10 is an output relay, 12a and 12b are first and second infrared bandpass filters, 13 is a semi-transmitting mirror, and 14 is a differential amplifier. Figure 1 Figure 4 Figure 2 Figure 3 Figure 5

Claims (1)

[Claims] 1. A lens for condensing radiation light from a moving red-hot metal body, and of the light condensed by this lens, a narrow wavelength range having different center wavelengths within a limited wavelength range. first and second infrared bandpass filters that transmit only light in a band; first and second infrared bandpass filters that receive transmitted light from the first and second infrared bandpass filters and convert it into an electrical signal; A photoelectric converter, a differential amplifier that determines the differential component of each of the above electrical signals, a DC converter that converts this amplified electrical signal into a DC signal, and a comparison amplifier that compares and amplifies the DC signal with a fixed DC reference level. A red-hot metal detector characterized by comprising: 2. A lens that focuses radiation light from a moving red-hot metal object, and is sensitive only to a narrow band of light that has different center wavelengths within a limited wavelength range among the light focused by this lens. a first and second photoelectric converter for converting the DC signal into an electric signal, a differential amplifier for determining the differential component of each of the electric signals, and a comparison amplifier for comparing and amplifying the DC signal with a constant DC reference level. A red-hot metal detector characterized by: