JPS6135672B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-frequency heating device, and an object of the present invention is to provide a high-frequency heating device equipped with an infrared detector that accurately detects the surface temperature of food.

In general, all objects having a temperature higher than absolute zero emit infrared rays, and the radiant energy W per unit surface area is expressed by the following equation.

W = εσT ⁴ ... where ε: emissivity σ: Stefan-Boltzman's constant T: absolute temperature 〓 The temperature of the pyroelectric detection element that receives this radiant energy changes, causing a change in the surface charge. This becomes the output. This surface charge is neutralized and disappears after a certain period of time.

In Fig. 1, 1 is a pyroelectric infrared detection element, 2
3 is a high resistance, 3 is an FET, and 4 is an output resistor, which constitute an infrared detector 5.

As shown in FIG. 2, the temperature of the floor 7 within the viewing range 6 of the infrared detector 5 is T ₁ , the emissivity of the floor 7 is ε ₁ , and there is an object within the viewing range 6 with a temperature T ₂ 8 has moved and is now in the state shown in FIG. In this case, the output resistance of the infrared detector 5 and the voltage waveform at both ends of the infrared detector 4 are expressed as a model.
In the case of T ₁ > T ₂ , as shown in Fig. 4, T ₁ >
In the case of T ₂ , it becomes as shown in FIG. Conversely, when changing from the state shown in Figure 3 to the state shown in Figure 2, the waveform will be as shown in Figure 5 when T ₁ < T ₂ and as shown in Figure 4 when T ₁ > T ₂ . becomes. Therefore,
In order to obtain continuous output with this pyroelectric detector, it is necessary to install a chopper between the pyroelectric detection element and the object to be measured to interrupt the infrared rays emitted from the object to be measured. . This situation is shown in FIG.
In Fig. 6, 5 is an infrared detector, 8 is an object to be measured, and 9 is a chopper. ε _c , T _c : Emissivity and absolute temperature of the chopper. ε ₂ , T ₂ : Emissivity and absolute temperature of the object to be measured. Then, the amount of change in the infrared light incident on the infrared detector 5 is ΔW=σ(ε _c T _c ⁴ −ε ₂ T ₂ ⁴ )..., and the output of the infrared detector is ΔW shown in the formula.
An AC output corresponding to W can be obtained. The waveform is T
If _c < T ₂ , the result will be as shown in Fig. 7, and if T _c > T ₂
In this case, the result will be as shown in FIG. In FIGS. 7 and 8, the polarities are reversed.

Figure 9 shows infrared detection when the temperature T ₂ of the object to be measured changes from the region T _c > T ₂ to the region T _c ≦T ₂ with T _c constant and the infrared chopping frequency constant. This is a model representation of the effective value of the AC component of the output voltage of the device 5. As can be seen from FIG. 9, for example, the temperature of the object to be measured where the output voltage of the infrared detector 5 is V ₀ is in the region of T _c > T ₂ and in the region of t _c < T ₂ shown in FIG. There are t ₀ ' and two points. Therefore, for example, when the output voltage from the infrared detector is V ₀ , it is difficult to determine whether the temperature of the object to be measured is t ₀ or t ₀ '. Here, in order to detect the disconnection of the chopper 9, light emitting parts 10' and 10'' are provided as shown in FIG. 6. For example, a photointerrupter 10 is provided. The position is adjusted so that the rising and falling phases of the output from the section 10'' substantially coincide with the center line of the alternating current component of the output of the infrared detector 5. At this time, the relationship between the output from the light receiving section 10'' of the photointerrupter 10 in Fig. 10 (a) and the output from the infrared detector 5 is shown in a model, as shown in Fig. 4 (b) when T _c > T ₂ . When T _c < T ₂ , the polarity is reversed from that in Figure 10 (c).

Therefore, when both the output A from the photointerrupter 10 and the output from the infrared detector 5 are added, if T _c < T ₂ , the solid line in FIG. 11 indicates T _c
>T ₂ , the waveform becomes as shown by the dotted line.
The waveform obtained when the output shown in FIG. 11 is passed through a chopping frequency _{of 0} and the low-frequency and high-frequency output components are cut by a bandpass filter having characteristics as shown in FIG. 12, for example, is as follows. In FIG. 13, the case where T _c <T ₂ is indicated by a solid line, and the case where T _c >T ₂ is indicated by a dotted line. As a result, as mentioned above, if only the output from the infrared detector 5 is used, for example, the output of V ₀ is divided into two parts of t ₀ and t ₀ '.
Although it was difficult to distinguish between the two because of the temperature of the point,
By configuring as described above, both outputs become clear as shown in FIG. By the way, the output from the infrared detector becomes larger than the intermittent output voltage (υ shown in FIG. 10A) of the photointerrupter. In other words, if the temperatures of the objects to be measured are very close to each other, as shown in Figure 14, by adding the output voltage model A of the photointerrupter and the output model waveform B from the infrared detector, the result will be as shown in C. The output waveform obtained by passing the output shown in C through a bandpass filter becomes as shown in D. Therefore, under the conditions of chopper temperature T _c and chipping frequency ₀ , the temperature of the measured object is T
When changing from the region _c > T ₂ to the region T _c < T ₂ , the AC effective value output after passing through the bandpass filter is the output voltage of the photointerrupter V _a , V _b , V _c , O Considering the case of (V _a > V _b > V _c > O), as shown in Figure 15, in the case of V _a , a, in the case of V _b , b, in the case of V _c , c, and in the case of O, It becomes as shown in O. Here, as shown in FIG. 15, the expected object to be measured (for example, frozen food)
Let T ₂ min be the minimum temperature of
Assuming that Tconmin is, for example, in the case of FIG. 15C, when the AC output voltage from the bandpass filter is below V _c , there are two temperatures at the same AC output voltage, and it is difficult to distinguish between the two temperatures. Therefore, in the case shown in FIG. 15C, the AC output is equal to or higher than V _c , that is, the lowest temperature at which Tconmin shown in FIG. 15 can be detected. However, in the characteristic shown in Fig. 15b, the AC voltage output at a temperature of Tconmin is V _b , and the AC output voltage from the bandpass filter when the temperature of the object to be measured is below Tconmin is always V b. If the detection device is set higher _than the V _b voltage, temperatures of T ₂ min or more can be sufficiently detected, and even in the case of the characteristics shown in FIG. The same can be said for b. Therefore, at the output obtained by adding the output of the photointerrupter and the output from the infrared detector and passing it through a bandpass filter, the The first set of
If the output voltage V of the photointerrupter shown in Figure 0 is selected, the magnitude of the AC output voltage and the temperature will always be as shown in Figure 15 a or b at the temperature of the object to be measured, and the two points shown in c or O There is no need to judge which temperature it is.

The above configuration is within the detection temperature range of the measured object.
The AC output voltage always has the same polarity, and the output at the temperature of the measured object below the detection temperature range is intended to be smaller than the output at the lowest detection temperature in the above detection temperature range. As mentioned above, by developing the same idea as the above method, for example, conversely, the AC output voltage can be lowered when the temperature of the object to be measured is high, and the AC output voltage can be increased when the temperature of the object to be measured is low. Similarly, a method of obtaining an output by subtracting the output of the infrared detector from the output of the photointerrupter shown in FIG. 10 and passing the obtained output through a bandpass filter is also considered. This characteristic is shown in FIG. 16 in the same manner as FIG. 15. That is, let the maximum temperature expected in the field of view from the infrared detector be T ₂ max, and let the maximum temperature in the control temperature range be Tconmax, and Tconmax
Let V _L min be _the AC output voltage of They have the same polarity, and at a temperature higher than Tconmax, the output is smaller than V _L min, making control easier.

Also, by inverting the polarity shown in Figure 10A and subtracting or adding the output in Figure 10B,
It is also possible to obtain the characteristics shown in FIG. 15 a or b or FIG. 16, and similar effects can be obtained.

Since the present invention has the above-described configuration, the temperature of the object to be measured can be accurately detected, and appropriate temperature control has become possible. Note that the present invention can be used not only for high-frequency heating devices but also for other electric heaters, gas-powered cooking devices, and the like.

[Brief explanation of the drawing]

Figure 1 is the circuit diagram of the infrared detector, Figures 2 and 3
The figure is a side view when detecting the temperature of the object to be measured, Figures 4 and 5 are waveform diagrams, and Figure 6 is a perspective view showing the arrangement of the infrared detector when using a chopper.
Figures 7 and 8 are waveform diagrams in Figure 6, Figure 9 is an AC effective value output waveform diagram when the chopper temperature and chopper frequency are kept constant and the temperature of the object to be measured is varied, and Figure 10 is A, B, and C are waveform diagrams showing the correlation between the output of the photocoupler light receiving section and the output from the infrared detector, and Figure 11 is the output waveform when the waveforms of A and B or A and C in Figure 10 are added. Figure 12 is a characteristic diagram of the band pass filter, Figure 13 is an output waveform diagram when the waveform in Figure 11 is passed through the band pass filter in Figure 12, Figure 14 A, B, C, and D are The output waveform diagram of each part when the temperature of the object to be measured is extremely lower than the chopper temperature, Figure 15 is the output waveform diagram when the temperature of the object to be measured changes when the photocoupler output voltage is changed,
FIG. 16 is an output waveform diagram when the photocoupler output and the output from the infrared detector are subtracted. 5... Infrared detector, 8... Measured object, 9...
Chiyotsupa, 10...Photointerrupter.

Claims (1)

[Claims] 1. In a high-frequency heating device that controls high-frequency output by detecting infrared rays emitted from the surface of food or a container containing food, there is no connection between the food and an infrared detector that detects infrared rays emitted from the surface of the food. , a chopper is provided to interrupt the infrared rays, and the infrared rays generated from the food surface are incident on the infrared detector in an alternating current manner, and a photocoupler is provided to detect the alternating current component of the output from the obtained infrared detector and the discontinuation of the chopper. After adding the intermittent output from this photocoupler, this added output is added to a bandpass filter that has a peak at a frequency that is approximately the same as the frequency at which the infrared rays are intermittent. A high-frequency heating device characterized by being equipped with a detection circuit.