JP2005083896A - Sensor circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems, wherein control, for example, for determining the amount of increase/decrease in the concentration of CO2 by the difference between an initial value when measurement is started and a result detected for each specified time for reducing an error, is not guaranteed, while an absolute value cannot be detected easily by variations, or the like of a sensor in a conventional gas sensor circuit, and influence depending on a usage environment is large. <P>SOLUTION: The sensor circuit comprises: the sensor for selectively detecting gas, such as carbon dioxide; a conversion section for converting the sensor output to a stable level; an A/D converter for converting the output of the conversion section from analog to digital by inputting; and a microcomputer for performing various control, based on the A/D conversion result. When the sensor output becomes abnormal, control is shifted from that by the A/D conversion result of the microcomputer to time control. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a sensor circuit using a sensor that selectively detects a gas such as carbon dioxide.

  Conventionally, in a sensor circuit (hereinafter referred to as a CO2 sensor) that selectively detects this kind of gas such as carbon dioxide, the conventional CO2 sensor is heated by an internal heater, and when a predetermined temperature is reached, the element is activated and the concentration of carbon dioxide is increased. A potential corresponding to is generated. The potential decreases from the initial value as the carbon dioxide concentration increases. The detection circuit uses this change to detect an increase or decrease in the carbon dioxide concentration with respect to the initial value based on the amount of change in the generated potential. For example, in an air conditioner, this detection value is used for controlling the oxygen supply amount.

FIG. 7 (a) shows a block diagram of a conventional sensor circuit. Sensor 1 is CO
The schematic configuration of the two sensors, the heater 1 is a heater unit installed in the sensor 1, and the element 1 is a gas reaction unit that reacts with carbon dioxide, which is the main component of the CO2 sensor, to generate a potential. The detection unit 1 amplifies and converts the minute output of the sensor 1 to a predetermined stable level.
FIG. 7 '(b) shows the detection state of the CO2 sensor output in the conventional example. Here, an explanation will be given of application in an air conditioner that can selectively take in oxygen from outside and supply it into the room. In this air conditioner, the oxygen supply amount is increased when the indoor carbon dioxide concentration is increased, and the oxygen supply amount is decreased and the indoor oxygen concentration is kept at a predetermined level when the carbon dioxide concentration is decreased. The relationship between the carbon dioxide concentration and the oxygen supply is that the presence of a person generally consumes oxygen and consequently increases carbon dioxide, so that the oxygen deficiency in the room is estimated (see, for example, Patent Documents 1 to 3). ).

The configuration described in Patent Document 1 describes that various controls are performed by fuzzy control using a CO2 sensor detection result. In the configuration described in Patent Document 2, it is described that detection accuracy is improved by intermittently connecting a CO2 sensor and a sensor output detection circuit. In the configuration of Patent Document 3, it is described that a plurality of CO2 sensors having different sensitivities are installed, and low-concentration gas is detected with high accuracy based on the difference between them.
These are intended to improve the detection accuracy of carbon dioxide by a CO2 sensor.
JP-A-5-44973 JP-A-7-27741 JP-A-9-33477

  However, conventionally, the carbon dioxide concentration is detected by the CO2 sensor. However, if the detected value does not change due to the failure of the CO2 sensor or the like, the carbon dioxide concentration is controlled to be low. There was a problem that oxygen could not be supplied sufficiently. In any case, the CO2 sensor is normal, and control is not particularly guaranteed for the detection result in a failure or irregular environment.

The present invention solves the above-described problem. A CO2 sensor that selectively detects a gas such as carbon dioxide, a conversion unit that converts a CO2 sensor output to a stable level, an output of the conversion unit, and an A / An A / D converter that performs D conversion, and is configured with a microcomputer that performs various controls based on the A / D conversion result. When the CO2 sensor output becomes abnormal, the A / D conversion result of the microcomputer 3 It is set as the structure which leaves | separates from control by.

  In order to solve the conventional problems, a sensor circuit of the present invention includes a sensor that selectively detects a gas such as carbon dioxide, a conversion unit that converts a sensor output to a stable level, and an output of the conversion unit. Consists of an A / D converter that performs analog / digital conversion (hereinafter A / D conversion) and a microcomputer (hereinafter referred to as microcomputer) that performs various controls based on the A / D conversion results, and the sensor output is "abnormal" When it becomes, it will separate from control by the A / D conversion result of a microcomputer, and will shift to time control.

  As a result, even if the output from the sensor becomes abnormal under conditions where the CO2 sensor is abnormal or the usage environment has changed, it is possible to shift to time control, so that the detection accuracy is not deteriorated.

  The sensor circuit of the present invention may impair the function of the CO2 sensor-equipped device even if the detection potential of the CO2 sensor does not change due to a failure or the like, or even if an output level at which the generated potential should not be generated is detected. Absent.

  Also, taking advantage of the possibility that the internal elements will stabilize and return to normal by holding the current for a long time, the sensor output is detected again after a predetermined time, and if it is a normal value, the control immediately returns to the control based on the A / D conversion result. By doing so, it is possible to return to the original fine control.

Moreover, it is possible to shift to the sensor control only when the CO2 sensor is surely normal, and it is possible to avoid the hunting state of the control and the time control based on the value of the CO2 sensor. Even if the sensor output does not become a normal value even after the reset operation, the power to the sensor circuit including the CO2 sensor is temporarily shut off at the SW section, and the sensor circuit is controlled by circuit reset control for supplying power again after a predetermined time. An opportunity to return.

In addition, it is possible to reduce a decrease in the chance of performing an immediate abnormality determination based on a slight level change and performing fine control based on the original detection result of the CO2 sensor.
In addition, it is possible to reduce the chance of performing fine control based on the original CO2 sensor detection result at a relatively low cost and easily.

  A first invention includes a sensor that selectively detects a gas such as carbon dioxide, a conversion unit that converts the sensor output to a stable level, and an A / D converter that inputs the output of the conversion unit and performs A / D conversion. And a microcomputer that performs various controls on the basis of the A / D conversion result. When the sensor output becomes abnormal, the microcomputer is separated from the control based on the A / D conversion result.

  In the second invention, after detecting the output from the sensor of the first invention as abnormal, the sensor output is detected again after a lapse of a predetermined time, and if it is a normal value, the control returns to the A / D conversion result. is there.

In the third invention, in particular, after detecting the output from any one of the sensors of the first and second inventions as abnormal, the result of detecting the sensor output again after a lapse of a predetermined time has become a normal value a plurality of times. In this case, the sensor determines that the sensor has returned to normal, and thereafter returns to control based on the A / D conversion result.

  The fourth invention has a SW circuit for turning on / off the power supply for any one of the sensors of the first to third inventions in particular, and when an abnormal output from the sensor is detected, the SW circuit supplies power to the sensor. After the supply is shut off and the state of the sensor is reset, power is again supplied to the sensor by the SW circuit.

  The fifth invention has a plurality of converters that amplify and convert the sensor output of any of the first to fourth inventions to a stable level, and the plurality of converters are set to different amplification factors. is there.

  In particular, the sixth aspect of the invention includes a conversion unit that amplifies and converts the sensor output of any one of the first to fifth aspects of the invention to a stable level and sets the amplification factors different from each other at least two circuits, and the conversion unit A switching unit for switching the input to the A / D conversion unit of the microcomputer, and the conversion unit connected to the A / D converter by the switching unit according to the level of A / D conversion, that is, the amplification factor is selected. .

  With this configuration, the function of the CO2 sensor-equipped device that has detected an output level that should not originally occur due to a failure of the CO2 sensor or a change in the usage environment is not impaired.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a flowchart of the CO2 sensor output of the first embodiment. When the detected potential of the CO2 sensor no longer changes due to a failure or the like, or when a high or low level where the generated potential should not be generated is detected, the CO2 sensor is judged to be abnormal, and the change was made by changing the sensor output. The control is shifted from the various controls based on the A / D conversion result of the microcomputer to the control using the time as a factor. Thus, even when the CO2 sensor becomes abnormal, the function of the CO2 sensor utilizing device (here, an air conditioner capable of supplying oxygen) is not impaired by this protection control.
As an example of time control, the oxygen supply amount is maximized for a predetermined time at the beginning of operation, and thereafter, the oxygen supply amount is controlled to be small for a predetermined time. After a long time has elapsed, the oxygen supply amount is controlled to be large for a predetermined time. Is repeated.

(Embodiment 2)
FIG. 2 is a flowchart of the CO2 sensor output in the second embodiment of the present invention. In the first embodiment, the function of the CO2 sensor using device is not impaired, but since it is time control, it is not a fine control based on the original detection result of the CO2 sensor.

On the other hand, there are various abnormal states of the CO2 sensor. Among them, there is a possibility that the internal elements are stabilized and returned to normal by holding the power supply for a long time.
In this embodiment, the CO2 sensor output is detected again after a predetermined time has elapsed, and if it is a normal value, the flow immediately returns to control based on the A / D conversion result. Thus, the original fine control can be restored.

(Embodiment 3)
A third embodiment will be described with reference to FIG.
In the configuration of the second embodiment, the CO2 sensor output is judged to be abnormal, and after leaving from the control based on the A / D conversion result of the microcomputer, the CO2 sensor output is temporarily ignored. When it is determined that the value is a normal value, the original CO2 sensor control is immediately restored. However, if the microcomputer detects that the CO2 sensor is not completely normal and is in an unstable state and its output accidentally falls within the normal range, the CO2 sensor output becomes an abnormal value again, and in the worst case, It becomes a hunting state of control by the value of the CO2 sensor and time control.

In this embodiment, after detecting an output abnormality from the CO2 sensor in order to solve the above-mentioned problem, when the result of detecting the CO2 sensor output again after a predetermined time has become a normal value for a plurality of times, The CO2 sensor is determined to have returned to normal, and thereafter the control is returned to control based on the A / D conversion result.
As a result, it is possible to shift to sensor control only when the CO2 sensor is surely normal, and problems that may occur due to the configuration of the second embodiment can be avoided.

(Embodiment 4)
A fourth embodiment will be described with reference to FIG. In the second to third embodiments, the control expects that the CO2 sensor once determined to be abnormal is naturally recovered by long-term energization. On the other hand, the CO2 sensor, in principle, obtains sensitivity due to carbon dioxide by activating the carbon dioxide detection element by a heater installed inside, but there are various possibilities for the cause of sensor abnormal output. There may be abnormal polarization of the detection element and malfunction of the detection circuit due to energization for a long time. Accordingly, there is a possibility that normal recovery cannot be achieved by simply waiting for a long time as in the above embodiment.

  The present embodiment solves this problem, and has a configuration of a sensor circuit having an SW unit for turning on and off the power supply to the detection circuit. With this configuration, when the sensor output does not become a normal value even after a predetermined time and a plurality of return operations, a circuit that temporarily cuts off power to the sensor circuit including the CO2 sensor at the SW unit and supplies power again after a predetermined time The sensor circuit is returned by reset control.

(Embodiment 5)
A fifth embodiment will be described with reference to FIG. In the first to fourth embodiments, the output of the sensor circuit is determined to be abnormal / normal, and various controls are performed based on the determination result. However, as the determination condition, the A / D conversion result of the microcomputer is set to a predetermined level or higher or below, but depending on the setting level, the CO2 sensor does not fail and detection of carbon dioxide due to its variation or aging The output may exceed the abnormal / normal judgment level due to a function change.

Therefore, in the above configuration, a sensor that is still functioning is ignored, and the opportunity for fine control by the sensor is reduced.
The present invention solves this problem, and has a plurality of converters that amplify and convert the output of the CO2 sensor to a stable level, set the plurality of converters to different amplification factors, and output the respective converters. A different microcomputer A / D conversion input is used.

  Here, an example in which the amplification factor of the conversion unit is set as conversion unit 1 <conversion unit 2 will be described. In this configuration, in the initial state, various controls are executed as the setting of the value of the conversion unit 1, that is, the A / D conversion 1. During the control period, when the output of the CO2 sensor or the detection circuit drops due to some abnormality and falls below the abnormality determination level, the value of the conversion unit 2, that is, the value of A / D conversion 2 is adopted. As a result, it is possible to reduce a decrease in the chance of performing an immediate abnormality determination based on a slight level change, which is a problem, and performing fine control based on the original CO2 sensor detection result.

At this time, the absolute value of the CO2 sensor output fluctuates, but the increase / decrease in the amount of carbon dioxide is determined based on the amount of change from the initial value with reference to the initial value, and various control amounts are changed according to the increase / decrease amount. The effects of fluctuations can be canceled.

(Embodiment 6)
A sixth embodiment will be described with reference to FIG. In the fifth embodiment, when a plurality of conversion units are provided and each of them is input to different A / D conversion units of the microcomputer, the microcomputer requires as many A / D conversion units as the number of conversion units. It will be. On the other hand, a device that performs various controls while detecting various ambient environments such as room temperature and humidity, such as an air conditioner, requires a large number of A / D ports. A microcomputer having a large number of A / D ports is relatively expensive, and there is a problem that the number of A / D ports is restricted so that a variety of sensing operations are required.
Therefore, in the present invention, the sensor output is amplified and converted to a stable level and at least two conversion circuits are set to different amplification factors, and the input from the conversion unit to the A / D conversion unit of the microcomputer is performed. A switching unit for switching is provided, and a conversion unit connected to the A / D converter by the switching unit, that is, an amplification factor is selected by the A / D conversion level. The control of the switching unit is easy to process at a normal port, and it becomes possible to select a conversion unit set to a multistage amplification result, that is, a plurality of amplification factors, without using a large number of A / D ports. Therefore, it is possible to reduce the chance of performing fine control based on the original CO2 sensor detection result at a relatively low cost and easily.

  As described above, the sensor circuit according to the present invention has a CO2 sensor-equipped device even if the detection potential of the CO2 sensor does not change due to a failure or the like, or even if an output level at which the generated potential should not be generated is detected. Therefore, the present invention can be applied not only to an air conditioner but also to an air purifier.

Flowchart of the first embodiment of the present invention Flowchart of the second embodiment of the present invention Flowchart of the third embodiment of the present invention The block diagram of the 4th Embodiment of this invention The block diagram of the 5th Embodiment of this invention The block diagram of the 6th Embodiment of this invention (A) is a block diagram of a conventional example (b) is a diagram showing an example of sensor detection change

Claims (6)

A sensor that selectively detects a gas such as carbon dioxide, a conversion unit that converts the sensor output to a stable level, and an A / D converter that performs analog / digital conversion (hereinafter referred to as A / D conversion) on the output of the conversion unit; It is composed of a microcomputer (hereinafter referred to as a microcomputer) that performs various controls based on the A / D conversion result, and when the sensor output becomes “abnormal”, it is separated from the control based on the A / D conversion result of the microcomputer. A sensor circuit that shifts to time control. The output from the sensor is detected as "abnormal", the sensor output is detected again after a lapse of a predetermined time, and if it is "normal", the control returns to the A / D conversion result. Sensor circuit. After detecting the output from the sensor as “abnormal”, when the result of detecting the sensor output again after a predetermined time has again become “normal”, it is determined that the sensor has returned to normal, The sensor circuit according to claim 1, wherein the control returns to the control based on the A / D conversion result. When the sensor circuit detects that the output from the sensor is “abnormal”, the power supply to the sensor is shut off by the SW circuit, the sensor state is reset, and then the SW circuit is turned on again. The sensor circuit according to claim 1, wherein power is supplied to the sensor by a circuit. 5. The sensor circuit according to claim 1, wherein the sensor circuit includes a plurality of conversion units that amplify and convert the sensor output to a stable level, and the plurality of conversion units are set to different amplification factors. A sensor unit which stabilizes the sensor output and amplifies and converts each with a different amplification factor; at least two conversion units; and a switching unit which switches the input from the conversion unit to the A / D conversion unit of the microcomputer. 6. The sensor circuit according to claim 1, wherein an amplification factor is selected according to a level of / D conversion.

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