Measuring and testing – Gas analysis – Moisture content or vapor pressure
Patent
1982-09-10
1985-02-26
Goldberg, Gerald
Measuring and testing
Gas analysis
Moisture content or vapor pressure
73 73, 219 1055B, G01W 100, H05B 668
Patent
active
045011478
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a control circuit for controlling the self-cleaning function of a humidity sensor, and its object is to switch the characteristics of a control circuit for a ceramic humidity sensor having a self-cleaning function through changes in a resistance value from the self-cleaning mode to the humidity detecting mode or vice versa so as to thereby ensure an accurate control of the temperature of its humidity responsive region in its self-cleaning mode and an improved humidity detecting performance in its humidity detecting mode.
With advances in the art of sensors and microcomputers, an automated cooking appliance has been put into practical use in which a humidity sensor is provided for sensing variations in the relative humidity in a heating chamber which are caused by the steam generated from the cooking food so as to thereby monitor the progress of cooking and then automatically detect the completion of the cooking or enabling the switching of an output level.
The humidity sensor, because of its very nature as a humidity detecting means, is constantly exposed to the smoke, steam, oil and so forth generated from the cooking food, with the consequence that the humidity responsive region of the sensor becomes fouled and unable to sense the humidity accurately after a long time of use. For a sensor whose humidity responsive region is made of ceramic material, that is, a so-called ceramic humidity sensor, a self-heating heater is installed on its humidity responsive surface and periodically energized to burn out such dirt and to restore its humidity responsive characteristics that is, a refresh operation of the sensor. A way to control such a heating temperature depends upon the thermistor property of the sensor.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a circuit arrangement which insures more accurate measurements of humidity and more accurate control of refresh temperatures by switching a humidity sensor control circuit when switching from its refresh operation mode to its humidity detection mode.
Specific embodiments of the present invention will now be described with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentally front view of a microwave oven to which a ceramic humidity sensor is incorporated;
FIG. 2 is a perspective view showing the appearance of the ceramic humidity sensor as a principal component;
FIG. 3 is an enlarged cross sectional view of a humidity responsive region of the ceramic humidity sensor as shown in FIG. 1;
FIG. 4 is a circuit diagram of a humidity sensor control circuit;
FIG. 5 is a thermistor characteristic of the humidity sensor;
FIG. 6(1) is a plot showing the output voltage v. resistance characteristic of the thermistor in the circuit as illustrated in FIG. 4;
FIG. 6(2) is a plot showing the relative humidity v. resistance characteristic of the humidity sensor;
FIG. 7 is a circuit diagram of a power supply circuit for a heater as shown in FIG. 4;
FIG. 8 is a diagrammatic view of time-wise variations of an input to the comparator as shown in FIG. 4;
FIG. 9 is a perspective view of a ceramic humidity sensor having a heater disposed over its humidity responsive region;
FIG. 10 is a circuit diagram of a humidity sensor control circuit.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 1 through 5, microwaves from a magnetron 1 are fed into the interior of an oven 3 by way of a waveguide 2 and then absorbed by the food to be cooked. An airflow generated by a cooling fan 4 used for cooling the magnetron 1, after cooling the magnetron 1, enters the interior of the oven 3 via a punched portion 5 of a wall of the oven 3 and exits a housing 8 via an opposite punched portion 6 and an air guide 7. A humidity sensor 9 which is disposed within the air guide 7 senses the relative humidity in the air outlet and in other words senses the relative humidity in the oven 3.
The humidity sensor 9, as shown in FIG. 2, has its humidity respo
REFERENCES:
patent: 3983527 (1976-09-01), Ohsato et al.
patent: 4080564 (1978-04-01), Nitta et al.
patent: 4261179 (1978-09-01), Dageford
patent: 4335293 (1980-06-01), Kobayashi et al.
patent: 4336433 (1980-07-01), Yokozeki et al.
patent: 4383158 (1980-12-01), Niwa
Goldberg Gerald
Matsushita Electric - Industrial Co., Ltd.
Williams Hezron
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