JPS6159447B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to an infrared temperature detection device that detects the temperature of food by detecting infrared rays emitted from the food, such as a microwave oven. The present invention relates to an infrared temperature detection device in which the output level does not change even if the frequency of the commercial power source changes when a synchronous motor that rotates in synchronization with the commercial power source is used.

Generally, an infrared temperature detection device that detects the temperature of an object by detecting infrared rays emitted from an object uses an infrared detection element that outputs a signal according to the amount of incident infrared rays, and an infrared detection element that outputs a signal according to the amount of incident infrared rays. It consists of a chopper that continuously outputs from the detection element, a chopper motor that drives the chopper, and a photo interrupter that detects the position of the chopper. A rotating synchronous motor is used, and typically a 24-pole type has a commercial power supply of 100V/50Hz and 100V/50Hz, respectively.
When the voltage is 100V/60Hz, it rotates at a speed of 250 rpm and 300 rpm, and if the tipper has a shape with three blades, the tipper frequency is (250 x 3) ÷ 60 = when the commercial power frequency is 50Hz. When it is 12.5Hz and 60Hz, it becomes (300 x 3) ÷ 60 = 15Hz. That is, the chopper frequency differs depending on the commercial power supply frequency. By the way, the chopper frequency and the output voltage of the infrared detection element have a relationship as shown in Figure 1. As is clear from the figure, the output voltage of the infrared detection element is larger as the chopper frequency is lower and smaller as the chopper frequency is higher. Become. For example, when the chopper frequency is 12.5 Hz, it is 44 mV, and when it is 15 Hz, it is 38 mV. When the chopper frequency is 12.5 Hz, the output voltage of the infrared detection element is about 14% higher than when it is 15 Hz. After the output voltage of this infrared detection element undergoes signal processing such as amplification, it is output as a signal corresponding to the temperature of the object, but what is the temperature of the object and the output voltage of the infrared temperature detection device at this time? , the relationship is as shown in Figure 2,
The curves indicated by A and B in the same figure show the characteristics when the chopper frequency is 12.5 Hz and 15 Hz.
In other words, due to different commercial power supply frequencies,
The output voltage level differs depending on the temperature of the object,
It's inconvenient.

The present invention takes into account the above-mentioned conventional problems, uses an active filter as a band-pass filter in the signal processing system of an infrared detection element, and sets the center frequency of the band-pass filter to a power supply frequency.
By setting the frequency between the chopper frequencies of 50Hz and 60Hz, the output of the infrared detection element, which varies depending on the power frequency, can be increased or decreased according to the power frequency using a bandpass filter.
This invention is designed to output approximately the same level of voltage for the same temperature of the object. Next, this invention will be explained in detail with reference to the drawings showing one embodiment thereof.

First, a microwave oven to which the present invention is applied,
To explain with reference to FIG. 3, which shows a cutaway front view, when microwave heating is performed using microwaves, microwaves oscillated from the antenna 2 of the magnetron 1 pass through the waveguide 3 from the feed port 4 to the cavity 5. Food (not shown) placed on a turntable 6 in the cavity 5 is heated by this microwave. On the other hand, when heating with a heater, hot air heated by a heater (not shown) is heated by a nozzle 9 installed in a nozzle case 8 covered with a heat insulating material 7 and mounted on the top plate 5' of the cavity 5. The food is fed into the cavity 5 and browned. Further, when heating the food mentioned above, the pulley 11 is rotated via the belt 10 by a drive source such as a motor, and the protrusion 1 of the connecting body 12 fixed to the pulley shaft 11' is rotated by the drive source such as a motor.
A turntable 6, whose part 2' is fitted into a recess (not shown) on the lower surface, rotates while being supported by a roller 13 provided at the bottom of the cavity 5, so as to prevent uneven heating and browning of the food. It's summery.

By the way, in general, all objects whose temperature is higher than the absolute temperature emit infrared rays corresponding to the temperature of the object, and the amount of infrared rays radiated per unit area W
is expressed by the formula W=ε・σ・T ⁴ . However, in the above equation, ε represents the emissivity, σ represents the Stefan-Boltzmann constant, and T represents the absolute temperature.

Next, an infrared temperature sensing device for food according to the present invention constructed based on this principle will be explained with reference to FIGS. 3 and 4. That is, the infrared rays emitted from the food pass through the microwave cut-off pipe 14, which is attached to the top plate 5' of the cavity 5 and is formed to have a length approximately at the cutoff wavelength of the microwave, so that the microwave does not leak. pass and further
Lithium tantalate, etc. contained in the shield case 17 is passed through the entrance port 17' of the shield case 17 installed in the detection box 16 attached to the detection box stand 15 fixed on the top plate 5'. Pyroelectric infrared detection element using single crystal 1
The infrared detecting element 18 receives the infrared rays and its temperature changes, causing a change in surface charge, and outputs a signal corresponding to the amount of incident infrared rays. However, since the surface charge of the infrared detection element 18 is neutralized and disappears after a certain period of time, it is necessary to interrupt the infrared rays incident on the infrared detection element 18 in order to obtain continuous output. That is, the infrared detection element 18 is sensitive only to intermittent light. Therefore, a chopper motor 20 consisting of a synchronous motor that rotates in synchronization with the commercial power supply is suspended from the outer surface of the shield case 17 by a mounting bracket 19, and a chopper 21 rotated by the chopper motor 20 is attached to the microwave cut-off pipe 14. and the entrance port 17' of the shield case 17. The chopper 21 has a shape in which a plurality of blades having the same width are arranged radially at equal intervals equal to the width of the blades. Therefore, the infrared rays incident on the infrared detection element 18 become intermittent light with a constant period,
Infrared rays emitted from the food and infrared rays emitted from the chopper 21 are alternately incident on the infrared detecting element 18 at regular intervals.

In FIGS. 3 and 4, 22 is a feed-through capacitor for noise prevention connected to the infrared detection element 18, and 23 is a solenoid mounted and fixed on the detection box stand 15, which is connected to the infrared detection element 18.
During operation, power is supplied to attract the plunger 24. 25 is a shutter fixed to the plunger 24 and slidably contacts the end face of the microwave cut-off pipe 14 to open and close the opening 14' of the microwave cut-off pipe 14; 26 is a shutter that attaches the shutter 25 in the direction of the microwave cut-off pipe 14; When the infrared detecting element 18 becomes inactive and the power supply to the solenoid 23 is stopped, for example, when the temperature of the food reaches the infrared detecting element 18 and the infrared detecting element 18 becomes inactive, the food is When heating by time control or when the heating operation is completed, the shutter 25 is moved to the left and the opening 14' of the microwave cut-off pipe 14 is closed by the shutter 25, so that water vapor and carbonized particles generated from the food are removed. , preventing the microwave from passing through the microwave cut-off pipe 14 and adhering to the infrared detection element 18 . 27 is a stopper for positioning the shutter 25 protruding from the end face of the microwave cut-off pipe 14; 28 is a photo interrupter for detecting the position of the chopper 21 attached to the mounting bracket 19 on both sides of the chopper 21; 29 is mounted near the photo interrupter 28 and detects the detection box 16 depending on its temperature characteristics.
Temperature compensation diode for detecting the temperature inside 3
0 and 31 are an intake port and an exhaust port of the cavity 5, respectively, and 32 is an air pipe communicating with the cavity 5. Cooling air is sent into the cavity 5 through the air pipe 32 by a blower motor (not shown), and this cooling The wind flows through the path shown by the arrow to cool each element for detection or control, and when the infrared detection element 18 detects infrared rays, the cooling air sent into the detection box 16 flows through the microwave cut-off pipe. Cavity 5 through 14
This microwave cut-off pipe 1
The flow of cooling air in the microwave cut-off pipe 14 prevents water vapor, carbonized particles, etc. generated from the heated food from adhering to the infrared detection element 18 through the microwave cut-off pipe 14.

Next, in FIG. 5 showing the signal processing system,
When the infrared rays that have become intermittent light due to the rotation of the tipper 21 are incident on the infrared detection element 18, an alternating current signal having an amplitude corresponding to the temperature difference between the food and the tipper 21 is generated in the infrared detection element 18 due to spontaneous polarization. This AC signal is connected to the positive DC power supply (+
Vcc), 1st FET (F1) and 1st and 2nd resistors R
1 and R2, the DC bias is applied and the signal is drawn out from the shield case 16, and then the DC is cut off by the first capacitor C1.Furthermore, since the signal obtained by the first capacitor C1 is weak, the first operational amplifier OP1 , third resistor R for feedback
3 and fourth and fifth resistors R4 and R for gain determination.
After that, the second operational amplifier OP2, the first and second variable resistors VR1, VR2 for gain adjustment, the second and third capacitors C2, C3, and the sixth to tenth Resistance R6
By passing through the narrowband bandpass filter BPF consisting of an active filter configured by ~R10, infrared noise and commercial power induction noise are cut out, the S/N ratio is improved, and the sine wave signal waveform is is converted to

On the other hand, the light from the light emitting diode L of the photo interrupter 28, whose both ends are connected to the ground terminal and the negative DC power supply -Vcc via the eleventh resistor R11 for current limiting,
The light is interrupted by the chopper 21, and upon receiving this interrupted light, the phototransistor FQ of the photointerrupter 28 is turned on and off. That is, the rotational position of the chopper 21 is detected by the photo interrupter 28. Then, the output signal of the photo interrupter 28 is transmitted to the first transistor Q1 connected to the photo transistor FQ and the first transistor Q1 connected to the photo transistor FQ.
After being amplified by the 12th resistor R12, which is the collector resistor of the transistor Q1, the Zener diode
ZD, the second transistor Q2 and the thirteenth to third transistors
Waveform shaping circuit WS consisting of 15 resistors R13 to R15
The waveform is shaped by
applied to the gate of F2, while the second FET, F2
The output signal of the bandpass filter BPF is applied to the drain of the filter. Then, in the synchronous rectifier SR, the sine wave signal inputted from the bandpass filter BPF is synchronously rectified by the position detection signal of the chopper 21 from the waveform rectifier circuit WS. When the food temperature is higher than that of the chopper 21, a positive differential voltage is outputted via the seventeenth resistor R17, and when the food temperature is lower than the temperature of the chopper 21, a negative differential voltage is outputted.
Next, the output signal of the synchronous rectifier SR is transmitted to the third operational amplifier OP3, the 18th resistor R18 for gain determination,
4th capacitor C4 and 19th resistor R1 for feedback
9, it is integrated by an integrating circuit IC configured as a well-known circuit and converted into a DC level signal, and is further connected to a fourth operational amplifier OP4 and a third variable resistor VR3.
and is amplified by a second amplifier circuit A2 constituted by the 20th to 22nd resistors R20 to R22, a voltage corresponding to the food temperature is obtained at the output terminal, and the drive of the magnetron 1 is controlled based on this voltage. Heating output is controlled.

By the way, as mentioned above, the bandpass filter BPF is provided for the purpose of cutting infrared noise and commercial power supply induced noise, so it is usually designed to match the chopper frequency. If configured as a CR circuit, the filter itself is configured as an active filter with gain, since the input signal is weak and is susceptible to induced noise and external hum. Furthermore, as shown in FIG. 6 showing the frequency characteristics, the center frequency ₀ of the bandpass filter BPF is 12.5Hz, which is the chopper frequency when the commercial power frequency supplied to the chopper motor 20 is 50Hz and 60Hz. 15
It is set to 13.75Hz, the midpoint of Hz. Therefore, as is clear from points a and b in the same figure,
When the tippa frequency is 12.5Hz and 15Hz,
A difference shown by c occurs in the output of the bandpass filter BPF. In other words, there is a difference in the gain of the bandpass filter BPF when the chopper frequency is 12.5Hz and 15Hz, and the ratio of these gains is α, and the infrared rays when the commercial power frequency is 50Hz and 60Hz, respectively. If β is the gain ratio of the output of the detection element 18, it is set so that α=β. Therefore, for the same food temperature, the commercial power frequency is 50Hz.
The difference in the output voltage of the infrared detection element 18 that occurs between the frequency of The same voltage is obtained for the same temperature.

As is clear from the above description, according to the infrared temperature detection device of the present invention, an infrared detection element that detects infrared rays emitted from an object, a chipper disposed between the object and the infrared detection element, and a synchronization with a commercial power supply. The commercial power frequency supplied to the chopper motor, which consists of a synchronous motor that rotates with
By providing a bandpass filter consisting of an active filter whose center frequency is set to a frequency between the respective chopper frequencies at 60Hz, even if the commercial power frequency supplied to the chopper motor differs between 50Hz and 60Hz, the Signals of the same level can be obtained for the same temperature of the object to be measured, and the temperature detection level becomes the same.

[Brief explanation of the drawing]

Figure 1 is a relationship diagram between the chopper frequency and the output voltage of an infrared detection element, Figure 2 is a relationship diagram between object temperature and output voltage of a conventional infrared temperature detection device, and Figures 3 and below are diagrams of the present invention applied to an oven range. 3 is a cutaway front view of a microwave oven, FIG. 4 is an enlarged view of the main parts of FIG. 3, FIG. 5 is a block diagram of the signal processing system, and FIG. 6 is a block diagram of the signal processing system. The figure shows the relationship between the chopper frequency and the output of the bandpass filter, and FIG. 7 shows the relationship between the temperature of the object and the output voltage. 18... Infrared detection element, 20... Chopper motor, 21... Chopper, BPF... Band pass filter.

Claims (1)

[Claims] 1. An infrared detecting element that detects infrared rays emitted from an object, a chopper disposed between the object and the infrared detecting element, and a chopper motor consisting of a synchronous motor that rotates in synchronization with a commercial power supply;
The commercial power frequency to which the output signal of the infrared detection element is input and supplied to the chopper motor is 50Hz.
An infrared temperature detection device equipped with a bandpass filter consisting of an active filter whose center frequency is set to a frequency between each chopper frequency at 60Hz.