JPH06242044A - Environment sensor - Google Patents

Abstract

PURPOSE:To produce a correct alarm even for drift of resistance by calculating a predetermined operating voltage when a decision is made that the output voltage has exceeded a predetermined range and sustaining the monitoring operation using a new predetermined operating voltage. CONSTITUTION:A sensor section S is connected in series with an output resistor Rc and a voltage Vc is applied to a series circuit of the sensor section S and the resistor Rc. A decision section D is connected with the joint P of the sensor section S and the resistor Rc and a microprocessor MPU, at the decision section D, receives an output voltage from the joint P through an analog/digital converter A/D and performs various processings based on a program stored in a program memory region ROM 1. Initial output voltage Vo and operating voltage Vs are additionally stored in the ROM 1. The microprocessor MPU is connected with an alarm section AL for producing an alarm depending on the processing results, a work area RAM 1, and a memory area RAM 2.

Description

Detailed Description of the Invention

[0001]

This invention relates to the presence of gas in the environment,
Further, the present invention relates to an environment sensor that detects the presence or absence of odor, etc., and particularly to such an environment sensor that has taken measures against aging.

[0002]

2. Description of the Related Art Conventionally, the state of the environment is detected by changing its own resistance value in response to the increase or decrease of environmental factors such as gas and odor (hereinafter abbreviated as gas). Environmental sensors are known which may include semiconductors. FIG. 3 schematically shows an electric circuit of a conventional environment sensor that detects, for example, a gas or the like. S is a sensor unit in which a resistance value R changes due to adsorption of a gas or the like, Rc is an output resistance, Vc is an applied voltage, V is the output voltage.

In operation, the output resistance Rc has a constant resistance value, and the sensor section S changes the resistance value R in accordance with the environmental condition of gas or the like. The change of the detection target can be detected, and when the output voltage V reaches a predetermined operating voltage Vs representing a predetermined gas concentration, an operation such as an alarm is performed. In general, since the sensitivity of the sensor unit S to gases and the like greatly depends on the temperature, it is customary to heat the sensor unit S to a high temperature of 300 ° C. to 400 ° C. before use, and this high heating temperature is used for the environmental sensor. Determines the stability of.

By the way, most of the time the sensor section S is used is placed in the air in a normal state in which there is no target substance such as gas, but it is placed in the air in this way. Even in this case, since the sensor unit S is heated by the heater, the resistance value R of the sensor unit itself changes with time due to the high temperature.

In general, the change with time of the output resistance Rc connected in series to the sensor section S is negligible as compared with the change with time of the resistance value R, so that it is placed in air in a normal state without gas. When the resistance value R of the operating sensor S changes over time, the output voltage V also fluctuates, so that the gas until the output voltage V reaches a predetermined operating voltage Vs for performing an operation such as an alarm. Etc. will have different concentrations. That is, in a sensor in which the resistance value R decreases as the concentration of gas or the like increases, first, when the resistance value R placed in the normal air without gas increases from the initial value due to aging. Assuming
The output voltage V becomes smaller than the initial value due to the change over time, and even if a predetermined gas concentration that should cause an alarm operation occurs in the environment, the output voltage V does not reach the predetermined operation voltage Vs and an alarm is issued. do not do. On the contrary, when the resistance value R of the sensor unit S, which is placed in the air in the normal state, becomes smaller due to the change with time, the output voltage V becomes larger than the initial value due to the change with time. The output voltage V reaches a predetermined operating voltage Vs at a gas concentration lower than a predetermined gas concentration at which an operation should occur, and an alarm is generated.

[0006]

As described above, when the resistance value R of the sensor section S in the normal air without gas changes with time or the like, the output voltage V does not always accurately represent the concentration of gas or the like. However, the environmental sensor that detects gas with a risk of explosion has a serious problem when such delay or loss of information occurs.

Therefore, it is an object of the present invention to generate an alarm with the same predetermined gas concentration at which the alarm should be generated even when the resistance value R of the sensor unit S fluctuates due to aging.

[0008]

In order to achieve this object, according to the present invention, a sensor portion whose resistance value changes according to the state of a detection target, and a sensor portion which changes corresponding to the change of the resistance value A circuit configuration for extracting a voltage as an output voltage; and a predetermined operating voltage setting means for setting the output voltage to be extracted from the circuit configuration as a predetermined operating voltage when the detection target changes to a predetermined state, In an environmental sensor configured to generate a signal when the output voltage reaches the predetermined operating voltage set by the predetermined operating voltage setting means, the initial output voltage when the detection target is in a normal state An initial output voltage setting means for setting as an initial output voltage, and the output voltage taken out from the circuit configuration when the detection target is in a normal state from the initial output voltage. A determining means for determining whether or not the output voltage has been deviated beyond a predetermined range, and when the determining means determines that the output voltage taken out from the circuit configuration deviates from the initial output voltage by a predetermined range or more. Using the fact that the ratio of the resistance value of the sensor unit when the detection target is in a normal state to the resistance value of the sensor unit when the detection target is in the predetermined state is always constant, and at least A new value of the predetermined operating voltage is calculated by using the output voltage just fetched, the initial output voltage, and the predetermined operating voltage, and is set in the predetermined operating voltage setting means. There is provided an environment sensor including a calculating / updating unit that updates the predetermined operating voltage with the new predetermined operating voltage.

[0009]

When the discriminating means discriminates that the output voltage just extracted from the circuit configuration deviates from the initial output voltage by a predetermined range or more due to a change with time or the like, the detection target is in a normal state. By utilizing the fact that the ratio of the resistance value of the sensor unit to the resistance value of the sensor unit when the detection target is in a predetermined state is always constant, the new value of the predetermined operating voltage is calculated and updated by the means. After the calculation, the predetermined operating voltage is updated to the new predetermined operating voltage and used. When a change with time occurs in this way, the predetermined operating voltage is updated to a new value so as to correspond to the accurate predetermined working gas concentration according to the amount of change over time, so false alarms and false alarms are avoided. It

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Prior to that, the operation of the present invention will be specifically described. Generally, the change with time of the output resistance Rc connected in series with the sensor unit S is negligible as compared with the change with time of the resistance value R, and the sensor unit S in the air in the normal state where no gas exists. Of the resistance value R (assumed to be Ra) of
If the gas concentration is constant regardless of the gas concentration value, the ratio Ra / Rg to the resistance value R (Rg) of the sensor portion S at a specific gas concentration is as follows: Can be considered to be constant. According to the present invention, by utilizing this fact, when the output voltage V changes with time, the value of the predetermined operating voltage Vs is also changed so as to represent the predetermined operating gas concentration. That is, the initial value of the output voltage V before changing with time is V0,
The resistance value R of the sensor unit S at that time is R0, the operating voltage whose sensitivity is adjusted in the initial stage before change with time is Vs, the resistance value R of the sensor unit S at that time is Rs, and next, after the change with time. When the value of the output voltage V is V1, the resistance value R of the sensor unit S at that time is R1, the operating voltage that should be set after the change over time is V1s, and the resistance value R of the sensor unit S at that time is R1s, By utilizing the fact that Ra / Rg is almost constant before and after the change with time, R0 / Rs = R1 / R1s holds, and from this, R1s = R1 (Rs / R0) (1). Further, after the aging, R1s / Rc = (Vc-V1s) / V1s holds, so that R1s = Rc (Vc-V1s) / V1s (2). If R1s is eliminated from the above formulas (1) and (2), then (R1 / Rc) (Rs / R0) = (Vc-V1s) / V1s, and from this formula, the predetermined operating voltage V1s after change over time is obtained.
Is

[0011]

[Equation 1]

[0012]

By the way, in the equation (3), (R1 / Rc) and (Rs / R0) are obtained as follows. First, R0 = Rc (Vc-V0) / V0 is established during normal times before aging, and Rs = Rc (Vc-Vs) / Vs is established at the working gas concentration before aging.

[0014]

[Equation 2]

Is obtained. Further, in normal times after the change over time, R1 / Rc = (Vc-V1) / V1 (5) holds. Substituting equation 4 and equation 5 into equation 3,

[0016]

[Equation 3]

[0017] After the change over time, by using the operating voltage V1s calculated in this way, it is possible to issue an alarm with an accurate predetermined operating gas concentration.

Based on the above, an embodiment of the present invention will be described. FIG. 1 is a block circuit diagram of an environment sensor according to an embodiment of the present invention. In the figure, similarly to the environment sensor shown in FIG. 3, an output resistance Rc is connected in series to a sensor unit S. The applied voltage Vc is supplied to the series body of the portion S and the output resistance Rc. The determination unit D is connected to a connection point P between the sensor unit S from which the output voltage is taken out and the output resistance Rc. In the determination unit D, the microprocessor MPU determines the output voltage from the connection point P as an analog signal.
It is input through the digital converter A / D, and various processes are performed based on the program stored in the program storage area ROM1. In addition to the program storage area ROM1, the initial output voltage V0 and the initial operating voltage Vs
In addition, the above-mentioned formula 6 for obtaining the operating voltage V1s after further change with time is stored. Microprocessor MP
An alarm unit AL for issuing an alarm when it is determined that an alarm is necessary as a result of processing is connected to U via an interface I / F, and stores a work area RAM1 and an output voltage value. A storage area RAM2 for the connection is connected. The alarm unit AL may be provided at another place such as the receiver.

The operation of the environment sensor of FIG. 1 will be described below with reference to the flowchart of FIG. Initially, the initial setting is performed, and the reference value of whether or not the output voltage V0 in the normal state at the initial time and the predetermined operating voltage Vs at the working gas concentration, which are stored in the storage area ROM1, have each changed with time. And stored in the storage area RAM2 for use as a reference value for monitoring gas and the like (step 102),
By reading the output voltage V from the connection point P via the analog / digital converter A / D, the monitoring operation regarding the presence or absence of gas generation is performed. The output voltage V read from the connection point P is the output voltage V0 or a predetermined operating voltage V
Like s, first, it is stored in the storage area RAM2 (step 104), and then compared with a predetermined operating voltage Vs,
If the output voltage V exceeds the predetermined operating voltage Vs (Y in step 106), an alarm operation such as ringing an alarm bell, displaying an alarm, transferring or notifying is performed (step 108).

As a result of the comparison, if the output voltage V is equal to or lower than the predetermined operating voltage Vs (N in step 106), then the output voltage V is compared with the initial output voltage V0 and whether there is a change with time. It is determined whether or not (step 110). If the output voltage V is within the predetermined range of the initial output voltage V0 (Y in step 110), it is considered that there is no change over time, and in step 106, the predetermined operating voltage Vs is set in the environment. It will be monitored whether or not gas, etc. was generated.

If the output voltage V is the initial output voltage V0
If it is determined that the deviation exceeds a predetermined range from N (step 110, N), this means that the resistance value R of the sensor unit S has changed due to aging, and therefore the predetermined operating voltage Vs is corrected. is necessary. Therefore, with the measured output voltage V as V1, the new predetermined operating voltage V1s is calculated by the above equation (6), and this is set as the new predetermined operating voltage Vs. When the calculation of is completed, V1 is set as a new initial output voltage V0 and stored in the storage area RAM2 (step 11).
2). After that, this newly set storage area RAM2
Based on the predetermined operating voltage and the output voltage at the initial stage stored in, the comparison and determination will be performed in steps 106 and 110.

Although the output voltage V measured at the connection point P is directly compared with the predetermined operating voltage Vs and the initial output voltage V0 in steps 106 and 110, the measured specific output is shown. Considering that the voltage V can take an erroneous value including, for example, a noise component,
A plurality of measured output voltages V are stored in the storage area RAM2, the plurality of stored output voltages V are averaged, and the average value is set as the output voltage V in step 106.
And 110 may be used. Further, although the comparison between the output voltage V and the output voltage V0 at the initial stage is shown to be performed every time the output voltage V is read from the connection point P, as an alternative method, a timer is provided so that there is no false alarm at night. It may be performed at a predetermined time such as.

Further, in the above embodiment, the present invention has been described by taking the configuration in which the output resistance Rc is connected in series to the sensor section S and the output voltage is taken out from the connection point P of the both, but in general, in such a sensor, In some cases, various resistors and / or capacitive and / or inductive resistors may be added for connection in order to improve the output voltage. For example, in order to improve the linearity of the output voltage, a resistor is connected in parallel to the sensor unit S, or the output voltage is not directly taken out from the connection point P but taken out through a resistor or a capacitor. In some cases, instead of taking the output voltage from the sensor, the output voltage is taken from both ends of the sensor unit S. Even in such a case, if the value of the resistance to be added is known, the sensor unit S may be changed before and after the change with time.
By utilizing the fact that the ratio of the resistance value R of Ra / Rg is constant, the predetermined operating voltage V1s after the aging can be calculated in the same manner.

[0024]

As described above, according to the present invention, when it is determined that the output voltage detected now deviates from the initial output voltage by more than a predetermined range due to the change with time,
By utilizing the fact that the ratio of the resistance value of the sensor section to the resistance value of the sensor section at a predetermined working gas concentration in the normal air without gas is always constant, a new value of the predetermined working voltage can be calculated. After the calculation, the new predetermined operating voltage is used to continue the monitoring operation. Therefore, even if the resistance value R of the sensor unit S fluctuates due to a change over time, the same predetermined gas concentration at which an alarm should be issued is generated. An alarm can be generated, and therefore false alarms and false alarms can be avoided.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing an environment sensor according to an embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of the environment sensor shown in FIG.

FIG. 3 is a circuit diagram for explaining a conventional environment sensor.

[Explanation of symbols]

 S Sensor section Rc Output resistance MPU Microprocessor ROM1 Storage area for programs, etc. RAM2 Storage area for output voltage, etc. AL Alarm section Vc Applied voltage V Output voltage V0 Initial output voltage Vs Predetermined operating voltage V1s New prescribed operating voltage

Claims (5)

[Claims] 1. A sensor unit whose resistance value changes according to the state of a detection target, a circuit configuration for extracting a voltage that changes according to the change of the resistance value as an output voltage, and the detection target up to a predetermined state. A predetermined operation voltage setting means for setting the output voltage to be taken out from the circuit configuration as a predetermined operation voltage when changed, the predetermined operation in which the output voltage is set in the predetermined operation voltage setting means. In an environmental sensor that generates a signal when a voltage is reached, an initial output voltage setting unit that sets the initial output voltage when the detection target is in a normal state as an initial output voltage, and the detection target is A discriminating means for discriminating whether or not the output voltage taken out from the circuit configuration in the normal state deviates from the initial output voltage by a predetermined range or more; The resistance value of the sensor unit when the detection target is in a normal state when the determination means determines that the output voltage that has just been taken out of the path configuration deviates from the initial output voltage by more than a predetermined range. , Utilizing the fact that the ratio to the resistance value of the sensor unit when the detection target is in the predetermined state is always constant, and at least the output voltage just taken out, the initial output voltage, and A calculation for calculating a new value of the predetermined operating voltage by using the predetermined operating voltage and updating the predetermined operating voltage set in the predetermined operating voltage setting means with the new predetermined operating voltage. -Environment sensor equipped with updating means. 2. The environment sensor according to claim 1, wherein the circuit configuration includes an output resistance connected in series with the sensor section, and the output voltage is taken out from a connection point between the output resistance and the sensor section. 3. When the discriminating means discriminates that the output voltage taken out from the circuit configuration deviates from the initial output voltage by more than a predetermined range when the detection target is in a normal state, The calculating / updating means updates the initial output voltage set in the initial output voltage setting means with the output voltage just fetched after updating with the new predetermined operating voltage. Or 2 environmental sensors. 4. The environment sensor according to claim 1, wherein the output voltage is an average value of a plurality of output voltages. 5. The environment sensor according to claim 1, wherein the sensor unit is a metal oxide semiconductor.