JP2012208074A - Temperature control device, gas detector, and temperature control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature control device capable of preventing excess temperature rise when temperature control of a control object is performed by utilizing the Wheatstone bridge circuit, a gas detector using the temperature control device, and a temperature control method.SOLUTION: In a combustible gas detector 1, when on/off of both changeover switches 523 and 524 is switched, a period in which the both changeover switches 523 and 524 become on is set for a predetermined overlapping period TX. Thus, in a high temperature setting period, predetermined high temperature (C2) is maintained, in a low temperature setting period, predetermined (lower than C2) low temperature (C1) is maintained, however, temperature of a heating resistor 34 does not sharply rise in switching of the both changeover switches 523 and 524.

Description

  The present invention relates to a gas detection device that can be used for, for example, concentration measurement or leakage detection of a combustible gas present in a detection atmosphere, and a temperature control device and a temperature control method that can be used for the gas detection device, for example. About.

  In recent years, research on fuel cells has been actively conducted as a high-efficiency, clean energy source due to social demands such as environmental protection and nature conservation. Among them, solid polymer fuel cells (PEFCs) and hydrogen internal combustion engines are expected as energy sources for home use and on-vehicle use due to advantages such as low temperature operation and high output density.

In these systems, for example, hydrogen, which is a flammable gas, is used as a fuel, so detection of gas leakage is cited as one of important issues.
As a gas detection device for detecting this type of hydrogen, for example, in a gas detection device using a Wheatstone bridge circuit, a heating resistor is provided as a part of the resistance of the circuit, and the amount of heat taken away from the heating resistor There is known a heat conduction type gas detection device that converts to heat conductivity and detects the gas concentration from the change in heat conductivity (see Patent Document 1).

JP 2004-354210 A

However, the above-described conventional technique has a problem that the study on the safety at the time of switching the temperature of the heating resistor is not sufficient.
For example, in a gas detection device using a Wheatstone bridge circuit, when one pair of heating resistors that switch the temperature using two switches is used as one of the four resistors of the Wheatstone bridge circuit, that is, they are arranged in parallel. When the two heating resistors are switched by two switches, the hydrogen concentration is calculated from the voltages at the low and high temperatures of the heating resistors controlled at two temperatures.

  However, when switching the temperature, if one of the switches is turned on and the other is turned off at the same time, both switches may be turned off momentarily. In this case, the resistance of the Wheatstone bridge circuit Becomes infinite. As a result, the temperature of the heating resistor rises excessively, and the thermal shock causes damage to the device, and there is a risk of ignition of the combustible gas, making it difficult to detect gas safely and stably. There was a problem.

  The present invention has been made in order to solve the above-described problems, and the purpose thereof is a temperature control device capable of preventing excessive temperature rise when performing temperature control of a controlled object using a Wheatstone bridge circuit, Another object of the present invention is to provide a gas detection device using the temperature control device and a temperature control method.

  (1) In the present invention, as a first aspect, a first side in which a first variable resistor and a switching resistor variable in resistance value to a different fixed value are connected in series via a first connection point; A Wheatstone bridge circuit in which a second side in which a fixed resistor and a heating resistor whose resistance value changes due to heat generation are connected in series via a second connection point; and the first connection point And a differential amplifier circuit to which a potential difference between the potential of the second connection point and the potential of the second connection point is supplied, and outputs the differential amplifier circuit to the Wheatstone bridge circuit so that the potential difference becomes zero And a temperature control device that controls the Wheatstone bridge circuit so as to satisfy an equilibrium condition and switches the resistance value of the switching resistor to a predetermined set temperature by switching the resistance value of the switching resistor. And said The resistor has a configuration in which a first switching resistor having a first resistance value and a second switching resistor having a second resistance value are connected in parallel, and the connection of the first switching resistor is turned on / off. And a second switch for turning on / off the connection of the second switching resistor, and when the first switch is turned off and the second switch is turned on to switch both switches, or When switching between both switches by turning on one switch and turning off the second switch, a predetermined period during which both switches are on is set.

  In the present invention, the switching resistor provided in a part of the Wheatstone bridge circuit has a configuration in which a first switching resistor having a first resistance value and a second switching resistor having a second resistance value are connected in parallel. And a first switch for turning on / off the connection of the first switching resistor and a second switch for turning on / off the connection of the second switching resistor. When the first switch is turned off and the second switch is turned on to switch both switches, or when the first switch is turned on and the second switch is turned off to switch both switches, both switches are turned on. A predetermined period is set.

  Therefore, unlike the prior art, when both switches are switched on and off, both switches are not instantaneously turned off, and thus the resistance of the Wheatstone bridge circuit does not become infinite.

  As a result, there is an effect that the heating resistor is not excessively heated and the device is not damaged. Further, when this temperature control device is used, for example, for detection of combustible gas, the heating resistor does not excessively increase temperature, so that there is a remarkable effect that there is no risk of ignition of the combustible gas.

  (2) In the present invention, as a second aspect, in the gas detector that includes the temperature control device according to the first aspect and detects the concentration of the combustible gas in the atmosphere to be detected, the first switch and the first switch 2 switch is driven, and control is performed to switch the energization state of the heating resistor at regular intervals so that the heating resistor has respective resistance values respectively corresponding to two preset temperatures. Energization control means, a resistance temperature detector whose resistance value changes due to a change in environmental temperature, which is the temperature in the atmosphere to be detected, and the heating resistor detected when the heating resistor is energized from the conduction control means Gas concentration calculating means for calculating the concentration of the combustible gas in the detected atmosphere, using the both-end voltage and an environmental temperature based on a voltage difference caused by a change in the resistance value of the resistance temperature detector, With this The features.

  In the combustible gas detection device of the second aspect, the gas concentration calculating means changes the voltage across the heating resistor detected when the heating resistor is energized to the heating resistor and the resistance value of the resistance temperature detector. The concentration of the combustible gas in the atmosphere to be detected can be calculated using the environmental temperature based on the voltage difference (temperature voltage) generated by the above.

  Note that the voltage across the heating resistor detected when the heating resistor is energized from the energization control means is detected when the heating resistor is controlled to one of two preset temperatures. Alternatively, detection may be performed at each (each set temperature) when the heating resistor is controlled to two preset temperatures.

  In particular, in this combustible gas detection device, since the temperature control device described above is used, both switches are not instantaneously turned off at the same time when both switches arranged in the Wheatstone bridge circuit are turned on / off. Therefore, the resistance of the Wheatstone bridge circuit does not become infinite when switching both switches. As a result, there is a remarkable effect that the heating resistor is excessively heated, and the thermal shock does not cause damage to the device or ignite the combustible gas.

  (3) In the present invention, as the third mode, the two set temperatures are preset such that the high temperature side of the set temperature is the first set temperature and the low temperature side is the second set temperature, and the gas concentration calculation And means for setting a voltage at both ends of the heating resistor detected at the first set temperature as a high temperature voltage and a voltage at both ends of the heating resistor detected at the second set temperature as a low temperature voltage. The humidity in the detected atmosphere is calculated based on the ratio of the low temperature voltage to the low temperature voltage, and the concentration of the combustible gas is corrected using the humidity.

  In the combustible gas detection device of the third aspect, the gas concentration calculation means uses the voltage at both ends of the heating resistor detected at the first set temperature as the voltage at the high temperature and the voltage across the heating resistor detected at the second set temperature. Is a low temperature voltage, the humidity in the detected atmosphere can be calculated based on the ratio between the high temperature voltage and the low temperature voltage, and the concentration of the combustible gas can be corrected using the humidity.

  In other words, since it is possible to ensure high resolution in the ratio between the high temperature voltage and the low temperature voltage, the humidity in the detected atmosphere can be accurately calculated, and this is used to correct the concentration of the combustible gas. As a result, the concentration of combustible gas can be detected with high accuracy.

  (4) In the present invention, as a fourth aspect, the first side in which the first fixed resistor and the switching resistor variable in resistance value to different fixed values are connected in series via the first connection point; A Wheatstone bridge circuit in which a second side in which a fixed resistor and a heating resistor whose resistance value changes due to heat generation are connected in series via a second connection point; and the first connection point A differential amplifier circuit to which a potential difference between the potential of the second connection point and the potential of the second connection point is supplied; and a first switching resistor having a first resistance value and a second switching value having a second resistance value as the switching resistor. A first switch for turning on / off the connection of the first switching resistor, and a second switch for turning on / off the connection of the second switching resistor. Using the temperature control device provided, the temperature of the heating resistor is set to a predetermined value A temperature control method for switching control at a time so that the potential difference becomes zero so that the output of the differential amplifier circuit is applied to the Wheatstone bridge circuit so that the Wheatstone bridge circuit satisfies the equilibrium condition. The first switch and the second switch are driven to switch the resistance values of the two switching resistors to switch the temperature of the heating resistor to a predetermined set temperature. When switching both switches by turning off the second switch and turning on the second switch, or when switching both switches by turning on the first switch and turning off the second switch, a predetermined period during which both the switches are turned on It controls to have.

  In the fourth aspect of the present invention, when the first and second switches are driven to switch the resistance values of both switching resistors and the temperature of the heating resistor is switched to a predetermined set temperature, the first switch is turned on. When switching both switches by turning off and turning on the second switch, or when switching both switches by turning on the first switch and turning off the second switch, it has a predetermined period during which both switches are turned on. Therefore, the same effects as the first aspect described above are achieved.

It is a whole block diagram of a combustible gas detection apparatus. It is explanatory drawing which shows the structure of the gas detection element used as the principal part of a combustible gas detection apparatus. It is a flowchart which shows the content of the gas concentration calculation process. (A) is explanatory drawing which shows structures, such as a change switch part, (b) is a timing chart which shows the switching state of a contact, (c) is a timing chart which shows the change of the temperature of a heating resistor. It is a flowchart which shows the control processing of both changeover switches. It is a timing chart which shows the relationship between switching control, the temperature of a heating resistor, and the voltage body between terminals.

Embodiments of the present invention will be described below with reference to the drawings.
Here, a combustible gas detection device that detects the concentration of a combustible gas such as hydrogen gas will be described as an example of a gas detection device including a temperature control device.

a) First, the configuration of the combustible gas detection device of this embodiment will be described.
FIG. 1 is an overall configuration diagram of a combustible gas detection device 1 to which the present invention is applied. 2A and 2B are explanatory views showing the configuration of the gas detection element 3 which is a main part of the combustible gas detection device 1. FIG. 2A is a plan view (however, the internal configuration is also partially shown), and FIG. It is AA sectional drawing in a).

[overall structure]
The combustible gas detection device 1 detects the concentration of combustible gas using a heat-conducting gas detection element 3. For example, the combustible gas detection device 1 is installed in a fuel cell vehicle and detects hydrogen leakage. Used for etc.

  As shown in FIG. 1, the combustible gas detection device 1 generates a control circuit 5 that drives and controls the gas detection element 3 (see FIG. 2), and a switching signal CG1 that controls the operation of the control circuit 5. Based on the detection signals V1 and VT obtained from the circuit 5, a microcomputer that executes various processes including at least a process (gas concentration calculation process) for calculating the gas concentration of the combustible gas contained in the gas to be detected (hereinafter referred to as “a microcomputer”). 7) and a start switch 9 for starting and stopping the control circuit 5 and the microcomputer 7 by turning on and off the power supply path from the DC power supply Vcc to the combustible gas detection device 1.

  The control circuit 5 (except for a heating resistor 34 and a temperature measuring resistor 35, which will be described later), the microcomputer 7 and the start switch 9 are configured on a single circuit board, and a gas separate from this circuit board. The detection element 3 is configured.

[Gas detection element]
Next, the gas detection element 3 will be described.
As shown in FIG. 2, the gas detection element 3 includes a flat base portion 30, and a plurality of electrodes 31 are formed on one surface (hereinafter referred to as “surface”) of the base portion 30, and the other surface (hereinafter referred to as “surface”). In the vicinity of the center of the base 30, a single recess 301 is formed along one direction of the base 30.

  The gas detection element 3 has a size of about several mm (for example, 3 mm × 3 mm) in both vertical and horizontal directions, and is manufactured by, for example, a micromachining technique (micromachining process) using a silicon substrate.

  The electrode 31 includes two electrodes 311 and 312 (hereinafter also referred to as “first electrode group”) arranged along one side of the base 30 (the lower side in FIG. 2A) and the other side. It consists of two electrodes 314 and 315 (hereinafter also referred to as “second electrode group”) arranged along the upper side in FIG. Among these, the electrodes 312 and 315 are also referred to as ground electrodes below. Moreover, as a material which comprises the electrode 31, aluminum (Al) or gold | metal | money (Au) is used, for example.

  The base 30 includes a silicon substrate 32 and an insulating layer 33 formed on one surface of the substrate 32, and a part of the substrate 32 so that the insulating layer 33 is partially exposed (here, approximately square). The diaphragm structure in which the recessed part 301 was formed is comprised by removing. That is, in the base portion 30, the insulating layer 33 side (the side where the substrate 32 is not removed) is the surface of the base portion 30, and the substrate 32 side (including the side where a part of the substrate 32 is removed) is the back surface of the base portion 30. It becomes.

  In the insulating layer 33, a linear heating resistor 34 wired in a spiral shape is embedded in a portion exposed on the back surface of the base 30 by the recess 301, and the side on which the second electrode groups 314 and 315 are formed. A resistance temperature detector 35 used for temperature measurement is embedded along the long side of the base 30.

Note that the insulating layer 33 may be formed of a single material, or may be formed of a plurality of layers using different materials. Further, as the insulating material constituting the insulating layer 33, for example, silicon oxide (SiO ₂₎ or silicon nitride (Si ₃ N ₄₎ is used.

  The heating resistor 34 is made of a conductive material having a large temperature resistance coefficient whose resistance value changes with its own temperature change, and the temperature measuring resistor 35 has an electrical resistance that changes in proportion to the temperature (in this embodiment, And a conductive material whose resistance value increases with increasing temperature). However, the heating resistor 34 and the temperature measuring resistor 35 are both made of the same resistance material, platinum (Pt) in this embodiment.

  The heating resistor 34 is connected to the first electrode group 311, 312 via a wiring 36 and a wiring film 37 embedded in the same plane as the heating resistor 34 is formed, and the resistance thermometer 35. Are connected to the second electrode groups 314 and 315 via a wiring film (not shown) embedded in the same plane as that on which the resistance temperature detector 35 is formed.

  In addition, as a material constituting the wiring 36 and the wiring film 37, the same resistance material as that of the heating resistor 34 and the temperature measuring resistor 35 is used. Further, the electrode 31 formed on the surface of the base 30 and the wiring film 37 formed inside the base 30 (insulating layer 33) are connected by a contact hole (connection conductor).

  That is, one end of the heating resistor 34 is connected to the electrode 311 and the other end is connected to the ground electrode 312, and the resistance temperature detector 35 is connected so that one end is connected to the electrode 314 and the other end is connected to the ground electrode 315. .

The gas detection element 3 configured as described above is used in a state where the back surface on which the concave portion 301 is formed is disposed so as to be exposed to the atmosphere to be detected.
[Control circuit]
Next, the configuration of the control circuit 5 will be described.

  As shown in FIG. 1, the control circuit 5 controls the energization of the heating resistor 34 and outputs a detection signal V1 corresponding to the voltage across the heating resistor 34, and the resistance temperature detector. And a temperature adjusting circuit 80 that outputs a temperature detection signal VT indicating the temperature of the atmosphere to be detected.

[Energization control circuit]
The energization control circuit 50 includes a bridge circuit (Wheatstone bridge circuit) 51 including the heating resistor 34, an amplification circuit 53 that amplifies the potential difference detected by the bridge circuit 51, and an output of the amplification circuit 53. A current adjustment circuit 55 that adjusts the current flowing through the bridge circuit 51 to increase or decrease is provided.

  The current adjustment circuit 55 is connected to the power supply line that supplies the DC power supply Vcc to the bridge circuit 51, and includes a transistor whose energization state (ON resistance) changes according to the adjustment signal C that is the output of the amplification circuit 53. Specifically, as the adjustment signal C is larger, the on-resistance is increased and the current flowing through the bridge circuit 51 is decreased. Conversely, as the adjustment signal is smaller, the on-resistance is decreased and flows through the bridge circuit 51. The current is configured to increase.

  The amplifier circuit 53 is connected in parallel between the operational amplifier 531, fixed resistors 532 and 533 connected to the non-inverting input terminal and the inverting input terminal of the operational amplifier 531, and the inverting input terminal and output terminal of the operational amplifier 531. It comprises a known differential amplifier circuit constituted by a fixed resistor 534 and a capacitor 535 connected to each other.

  That is, when the input voltage of the non-inverting input terminal is larger than the input voltage of the inverting input terminal, the adjustment signal C that is the output of the amplifier circuit 53 increases (and the current flowing through the bridge circuit 51 decreases), and conversely. When the input voltage at the non-inverting input terminal is smaller than the input voltage at the inverting input terminal, the adjustment signal C is reduced (and the current flowing through the bridge circuit 51 is increased).

  The bridge circuit 51 includes a heating resistor 34, two fixed resistors 511 and 512, and a variable resistor 52 that can switch a resistance value. The fixed resistor 511 and the heating resistor 34, the fixed resistor 512, and the variable resistor 52 are connected to each other. Each of the series circuits is connected in series, and in each series circuit, each end PG on the side of the heating resistor 34 and the variable resistor 52 is grounded, and each end on the side of the fixed resistors 511 and 512 is connected to the power supply side (current adjustment circuit 55). It is configured by connecting.

  The connection point P + between the fixed resistor 511 and the heating resistor 34 is connected to the non-inverting input terminal of the operational amplifier 531 through the fixed resistor 532, and the connection point P− between the fixed resistor 512 and the variable resistor unit 52 is Are connected to the inverting input terminal of the operational amplifier 531 through the fixed resistor 533. Further, the potential at the connection point P + is supplied to the microcomputer 7 as the detection signal V1.

  The variable resistance unit 52 includes two fixed resistors (first fixed resistor 521 and second fixed resistor 522) having different resistance values and the first and second fixed resistors 521 and 521 according to the switching signal CG1 from the microcomputer 7. The switch 520 (that is, a pair of switches of the first switch 523 and the second switch 524) that effectively operates one of the switches 522, and the resistance of the variable resistor unit 52 by both the switches 523 and 524 By switching the value, the balance (equilibrium state) of the bridge circuit 51 can be changed.

  Specifically, the first changeover switch 523 switches on / off of the first fixed resistor 521, and the second changeover switch 524 switches on / off of the second fixed resistor 522.

  The first fixed resistor 521 has a resistance value at which the heating resistor 34 becomes the first set temperature CH (for example, 400 ° C.), and the second fixed resistor 522 has the resistance value at which the heating resistor 34 has the first set temperature CH. It has a resistance value that becomes a second set temperature CL (for example, 300 ° C.) set lower. Therefore, the first changeover switch 523 is a contact H for switching the heating resistor 34 to the high temperature side, and the second changeover switch 524 is a contact L for switching the heating resistor 34 to the low temperature side (see FIG. 4).

  In the energization control circuit 50 configured as described above, when energization from the DC power source Vcc to the bridge circuit 51 is started, the potential difference generated between the connection points P + and P− in the amplifier circuit 53 and the current adjustment circuit 55 becomes zero. Thus, the current flowing through the bridge circuit 51 is adjusted. As a result, the resistance value (and hence the temperature) of the heating resistor 34 is controlled to a constant value (and thus the first set temperature CH or the second set temperature CL) determined by the variable resistance unit 52.

  Specifically, when the content (concentration) of the combustible gas in the atmosphere to be detected changes and the amount of heat taken away by the combustible gas becomes larger than the amount of heat generated by the heating resistor 34, the heating resistance As the temperature of the body 34 decreases, the resistance value of the heating resistor 34 decreases. Conversely, when the amount of heat taken away by the combustible gas is smaller than the amount of heat generated by the heating resistor, the temperature of the heating resistor 34 rises, and the resistance value of the heating resistor 34 increases.

  On the other hand, when the resistance value of the heat generating resistor 34 decreases, the amplifier circuit 53 and the current adjusting circuit 55 increase the current flowing through the bridge circuit 51 and thus the amount of heat generated by the heat generating resistor 34. When the resistance value of the resistor 34 increases, the current flowing through the bridge circuit 51, and hence the amount of heat generated by the heating resistor 34, is reduced, so that the resistance value (and thus the temperature) of the heating resistor 34 is kept constant. .

  In other words, from the detection signal V1 representing the potential at the connection point P +, the magnitude of the current flowing through the heating resistor 34, that is, the amount of heat necessary for keeping the temperature (resistance value) of the heating resistor 34 constant (and further, , The amount of heat taken away by the combustible gas), and the amount of heat becomes a magnitude corresponding to the gas concentration of the combustible gas, so that the gas concentration of the combustible gas can be determined from the detection signal V1. In detail, when calculating the gas concentration of the combustible gas, the correction is performed by using the humidity H in the detected atmosphere, which will be described in “gas concentration calculation process” described later.

[Temperature measurement circuit]
Next, the temperature adjustment circuit 80 includes a bridge circuit (Wheatstone bridge) 81 including the resistance temperature detector 35 and an amplification circuit 83 that amplifies the potential difference obtained from the bridge circuit 81.

  The amplifier circuit 83 is connected in parallel between the operational amplifier 831, fixed resistors 832 and 833 connected to the non-inverting input terminal and the inverting input terminal of the operational amplifier 831, and the inverting input terminal and the output terminal of the operational amplifier 831. It consists of a known differential amplifier circuit constituted by a fixed resistor 834 and a capacitor 835 connected to each other.

  The bridge circuit 81 includes a resistance temperature detector 35 and three fixed resistors 811, 812, and 813. The fixed resistor 811 and the resistance temperature detector 35, and the fixed resistor 812 and the fixed resistor 813 are connected in series. Among them, each end on the temperature measuring resistor 35 and the fixed resistor 813 side is grounded, and each end on the fixed resistors 811 and 812 side is connected to the DC power source Vcc.

  The connection point P− between the fixed resistor 811 and the resistance temperature detector 35 is connected to the inverting input terminal of the operational amplifier 831 via the fixed resistor 833, and the connection point P + between the fixed resistor 812 and the fixed resistor 813 is connected to the fixed resistor. It is connected to the non-inverting input terminal of the operational amplifier 831 through 832. The output of the operational amplifier 831 is supplied to the microcomputer as a temperature detection signal VT.

The resistance temperature detector 35 is set so that the temperature detection signal VT becomes a reference value when the temperature of the detected atmosphere to which the gas detection element 3 is exposed is a preset reference temperature.
Then, as the temperature of the atmosphere to be detected changes, the resistance value of the resistance temperature detector 35 changes to generate a potential difference, and an amplified version of this potential difference is output as the temperature detection signal VT.

  In connection between the gas detection element 3 and the control circuit 5, the electrode 31 (311, 312, 314, 315) of the gas detection element 3 is connected to the connection point P + of the energization control circuit 50 and the electrode 314 is connected to the electrode 311. The ground electrodes 312 and 315 are connected to a common ground line for the control circuit 5 at a connection point P− of the temperature adjustment circuit 80.

[Microcomputer]
The microcomputer 7 is a storage device (ROM, RAM, etc.) that stores various programs and data for executing gas concentration calculation processing, a CPU that executes programs stored in the storage device, and inputs and outputs various signals. For example, a well-known device including an IO port, a timer for timekeeping, and the like.

  Here, the signal level of the detection signal V1 detected at the first set temperature CH (400 ° C.) is the high temperature voltage (high temperature side heater voltage) VH1, and the detection signal detected at the second set temperature CL (300 ° C.). The signal level of V1 is referred to as a low temperature voltage (low temperature heater voltage) VL1, and the signal level of the temperature detection signal VT read from the temperature adjustment circuit 80 is referred to as a temperature voltage VT.

  In the storage device, temperature conversion data representing the correlation between the environmental temperature T and the temperature voltage VT in the detected atmosphere, the humidity H and the high temperature voltage VH1, the low temperature voltage VL1, and the temperature voltage VT in the detected atmosphere. Conversion data representing the correlation between the high-temperature voltage VH1 or the low-temperature voltage VL1 (in this embodiment, the high-temperature voltage VH1 is used) and the gas concentration X of the combustible gas. It is remembered. Each conversion data specifically includes conversion map data, a conversion calculation formula, and the like, and is created in advance based on data obtained through experiments or the like.

  The humidity conversion data includes voltage ratio conversion map data representing a correlation between the environmental temperature T (and thus the temperature voltage VT) and a voltage ratio VC (0) described later, and a voltage ratio difference ΔVC and humidity H described below. Humidity conversion map data representing the correlation is included. Further, the concentration conversion data includes high temperature voltage conversion map data representing a correlation between the temperature voltage VT and a high temperature voltage VH1 (0) described later, a high temperature voltage VH1 and a humidity H, and a high temperature voltage change ΔVH1 described below. (H) includes humidity voltage change conversion map data, temperature voltage VT and high temperature voltage VH1, and gas sensitivity conversion map data indicating a correlation between gas sensitivity G (VT) described later. Yes.

b) Next, the operation in the combustible gas detection device 1 of the present embodiment will be described.
[Gas concentration calculation processing]
Here, the gas concentration calculation processing executed by the CPU of the microcomputer 7 will be described with reference to the flowchart shown in FIG.

  The microcomputer 7 is activated when power supply from the DC power source Vcc is started by turning on the activation switch 9, and after initializing each part of the microcomputer 7, the gas concentration calculation process is started. In addition, the first changeover switch 523 and the second changeover switch 524 are turned on to start energization of the heating resistor 34 and energization of the resistance temperature detector 35.

  In the calculation for obtaining the gas concentration X, the gas concentration X is obtained using the concentration conversion data from either or both of the low temperature voltage VL1 and the high temperature voltage VH1 (in this embodiment, the gas concentration X is obtained from the high temperature voltage VH1. Furthermore, there is a method in which the environmental temperature T is obtained from the temperature voltage VT using the temperature conversion data, and the gas concentration X as the calculation result is corrected using only the environmental temperature T as the calculation result. However, here, the gas concentration X is obtained using the humidity H in addition to the environmental temperature T.

  When this process (gas concentration calculation process) is executed, first, in S110, the low temperature voltage VL1 and the high temperature voltage VH1 are acquired from the energization control circuit 50, and the temperature voltage VT is acquired from the temperature adjustment circuit 80.

Here, the process of obtaining the low temperature voltage VL1 and the high temperature voltage VH1 will be described in detail with reference to FIG.
Here, the resistance value of the bridge circuit 51, that is, the set temperature of the heating resistor 34 is set to the second setting for a certain period of time TW (for example, 200 msec) (hereinafter referred to as “low temperature measurement period”) by the switching signal CG1. After the temperature CL is maintained, the setting is switched, and control is performed to maintain the first set temperature CH for a certain period of time TW (for example, 200 msec) again (hereinafter referred to as “high temperature measurement period”).

  Specifically, as shown in FIGS. 4A and 4B, the operation of turning on the first changeover switch 523 (contact H) and turning off the second changeover switch 524 (contact L) is performed over a high temperature setting period. By maintaining, that is, by maintaining the operation of connecting the first fixed resistor 521 (for high temperature) as the resistance of the bridge circuit 51 over the high temperature setting period, the first set temperature CH is maintained.

  Then, after the high temperature setting period ends, the operation of turning off the first changeover switch 523 and turning on the second changeover switch 524 is maintained over the low temperature setting period, that is, as the resistance of the bridge circuit 51 (low temperature The operation of connecting the second fixed resistor 522 is maintained at the second set temperature CL by maintaining the operation for the low temperature set period.

  In particular, in the present embodiment, as shown in FIG. 4B, when turning on / off the two switches 523 and 524, a predetermined overlap period TX (for example, 1.0 msec to 10 msec) is set. A period during which both the changeover switches 523 and 524 are turned on is set over a predetermined value. The overlap period TX is set for both switching from the high temperature setting period to the low temperature setting period and switching from the low temperature setting period to the high temperature setting period. At the start of the control, a period in which both the changeover switches 523 and 524 are turned on is set over the overlap period TX.

  Thereby, as shown in FIG.4 (c), the temperature of the heating resistor 34 changes. That is, the predetermined high temperature (C2) is maintained in the high temperature setting period, and the predetermined low temperature (C1) (lower than C2) is maintained in the low temperature setting period. Therefore, the temperature of the heating resistor 34 does not rise rapidly when the two changeover switches 523 and 524 are switched.

  Next, the operation (switching control) of both the changeover switches 523 and 524 described above will be described in more detail with reference to the flowchart of FIG. 5 and the timing chart of FIG. FIG. 6 shows changes in the temperature and both-end voltage of the heating resistor 34 accompanying the switching operation.

  As shown in FIGS. 5 and 6, since both the switches 523 and 524 (contacts H and L) are turned on at the same time when the control is started, the temperature of the heating resistor 34 is controlled to the lowest temperature.

  Accordingly, in S200, only the second changeover switch 524 is turned off after a predetermined overlap period TX has elapsed since both the changeover switches 523 and 524 are turned on. Thereby, the temperature of the heating resistor 34 is controlled to a high temperature (C2).

In subsequent S210, the high-temperature voltage VH1 is read.
In subsequent S220, after the OFF period of the second changeover switch 524 has elapsed, the second changeover switch 524 is also turned on. That is, both changeover switches 523 and 524 are both turned on. Thereby, the temperature of the heating resistor 34 is controlled to the lowest temperature.

  In subsequent S230, only the first changeover switch 523 is turned off after the overlap period TX has elapsed since both the changeover switches 523 and 524 are turned on. The temperature of the heating resistor 34 is controlled to a low temperature (C1).

In subsequent S240, the low temperature voltage VL1 is read.
In subsequent S250, the first changeover switch 523 is also turned on after the first changeover switch 523 has been turned off. That is, both changeover switches 523 and 524 are both turned on.

Thereafter, the same operation is repeated, and the heating state of the heating resistor 34 is periodically repeated to a high temperature or a low temperature.
As a result, as shown in FIG. 6, the voltage between the terminals does not rise suddenly and the temperature of the heating resistor 34 does not rise suddenly when the two switches 523 and 524 are switched.

  In parallel with this, the low-temperature voltage VL1 is detected during the low-temperature measurement period, the high-temperature voltage VH1 is detected during the high-temperature measurement period, and the temperature voltage VT is detected at any timing in both periods. In the present embodiment, the temperature voltage VT is detected during the high temperature measurement period.

Returning to FIG. 3, in S120, the voltage ratio VC is calculated using the low temperature voltage VL1 and the high temperature voltage VH1 acquired in S110 as input values of the following equation (1).
VC = VH1 / VL1 (1)
In parallel with this, in S130, based on the temperature voltage VT acquired in S110 and the map data for voltage ratio conversion, the gas concentration X and the humidity H at the environmental temperature T (and thus the temperature voltage VT) are obtained. The voltage ratio VC (0) when is zero is calculated.

  In S140, the voltage ratio difference VC in the ambient temperature T (and thus the temperature voltage VT) is obtained by using the voltage ratio VC calculated in S120 and the VC (0) calculated in S130 as input values of the following equation (2). Is calculated.

ΔVC = VC−VC (0) (2)
Next, in S150, the humidity H at the voltage ratio difference ΔVC is calculated based on the voltage ratio difference ΔVC calculated in S140 and the humidity conversion map data.

  In parallel with this, in S160, based on the high temperature voltage VH1, the temperature voltage VT acquired in S110, and the high temperature voltage conversion map data, the gas concentration at the ambient temperature T (and thus the temperature voltage VT). A high-temperature voltage VH1 (0) when X and humidity H are zero is calculated.

  Subsequently, in S170, the high temperature voltage VH1 obtained in S110, the humidity H calculated in S150, and the humidity voltage change conversion map data are provided by the humidity H of the high temperature voltage VH1. A high-temperature voltage change ΔVH1 (H) that represents the voltage change is calculated.

  In S180, the high-temperature voltage VH1 acquired in S110, the high-temperature voltage VH1 (0) calculated in S160, and the high-temperature voltage change ΔVH1 (H) calculated in S170 are expressed by the following equation (3). As an input value, a high-temperature voltage change ΔVH1 (G) representing a voltage change caused by the combustible gas in the high-temperature voltage VH1 is calculated.

ΔVH1 (G) = VH1−VH1 (0) −ΔVH1 (H) (3)
In parallel with this, in S190, based on the high temperature voltage VH1, the temperature voltage VT acquired in S110, and the gas sensitivity conversion map data, the environmental temperature T (and thus the temperature voltage VT) is determined for the high temperature voltage VH1. ) Gas sensitivity G (VT) representing the sensitivity (in units of the reciprocal of the gas concentration X) for the combustible gas set in advance.

  Finally, in S200, the gas concentration of the combustible gas is obtained by using the high-temperature voltage change ΔVH1 (G) calculated in S180 and the gas sensitivity G (VT) calculated in S190 as input values of the following equation (4). X is calculated, and the process returns to S110.

X = ΔVH1 (G) / G (VT) (4)
As described above, in this process, the changeover signal CG1 is output to the changeover switch unit 520 every cycle time TW, so that the connection point P− between the fixed resistor 512 and the variable resistor unit 52 is connected to the end PG (variable resistor unit 52). Is switched from one of the first and second fixed resistors 521 and 522 to the other of the first and second fixed resistors 521 and 522, whereby the high-temperature voltage VH1 and the low-temperature The hour voltage VL1 and the temperature voltage VT are acquired. Then, the ambient temperature T is obtained from the temperature voltage VT, and further, the humidity H in the detected atmosphere is obtained from the ratio of the high temperature voltage VH1 and the low temperature voltage VL1, and the gas concentration X is determined using these environmental temperature T and humidity H. I am trying to correct it.

[effect]
As described above, in the combustible gas detection device 1 of the present embodiment, when the on / off of both the changeover switches 523 and 524 is switched, both the changeover switches 523 and 524 are both over a predetermined overlap period TX. The period for turning on is set. Thereby, the predetermined high temperature (C2) is maintained in the high temperature setting period, and the predetermined low temperature (C1) (C1) is maintained in the low temperature setting period, but at the time of switching between the changeover switches 523 and 524, The temperature of the heating resistor 34 does not rise rapidly.

  That is, in the present embodiment, by setting the above-described overlap period TX, when both the switches 523 and 524 are switched, the both switches 523 and 524 are not instantaneously turned off. Resistance never becomes infinite. As a result, the heating resistor 34 does not rise excessively, so that the apparatus is damaged by the thermal shock caused by the excessive rise in temperature, or the combustible gas is ignited when the concentration of the combustible gas is high. There is a remarkable effect that there is nothing to do.

[Relationship with Claims]
In the present embodiment, the energization control circuit 50 corresponds to the energization control means, and the microcomputer 7 corresponds to the gas concentration calculation means.

[Other Embodiments]
As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, In the range which does not deviate from the summary of this invention, it is possible to implement in various aspects.

  (1) For example, in the said embodiment, although the temperature control circuit of the structure mentioned above was used for the combustible gas detection apparatus, it can utilize for various other control apparatuses. For example, the present invention can be applied to a humidity detection device that detects the humidity of the atmosphere to be detected.

  (2) In the combustible gas detection device 1 of the above embodiment, the gas concentration X is calculated using the humidity H in the atmosphere to be detected. However, the present invention is not limited to this. The gas concentration X may be calculated using the both-ends voltage (VH1, VH2) of the body and the temperature voltage VT of the resistance temperature detector.

  DESCRIPTION OF SYMBOLS 1 ... Combustible gas detection apparatus, 3 ... Gas detection element, 5 ... Control circuit, 7 ... Microcomputer, 9 ... Starting switch, 34 ... Heating resistor, 35 ... Resistance temperature detector, 50 ... Current supply control circuit, 51 ... Bridge Circuit 52, variable resistance unit 55 55 current adjustment circuit 80 temperature control circuit 81 bridge circuit 87 switching circuit 511 512 521 522 fixed resistor 520 changeover switch 521 522 ... switching resistor, 523, 524 ... changeover switch, CH ... first set temperature, CL ... second set temperature, TW ... cycle time

Claims (4)

The first fixed resistor and a switching resistor variable to a fixed value different in resistance value are connected in series via the first connection point, and the resistance value changes due to heat generation with the second fixed resistor. A Wheatstone bridge circuit in which a heating resistor and a second side connected in series via a second connection point are connected in parallel;
A differential amplifier circuit to which a potential difference between the potential of the first connection point and the potential of the second connection point is supplied;
Have
The output of the differential amplifier circuit is applied to the Wheatstone bridge circuit so that the potential difference becomes zero, and the Wheatstone bridge circuit is controlled so as to satisfy an equilibrium condition.
A temperature control device for switching and controlling the temperature of the heating resistor to a predetermined set temperature by switching a resistance value of the switching resistor;
The switching resistor has a configuration in which a first switching resistor having a first resistance value and a second switching resistor having a second resistance value are connected in parallel, and the connection of the first switching resistor is turned on. A first switch that turns off and a second switch that turns on and off the connection of the second switching resistor;
When the first switch is turned off and the second switch is turned on to switch both switches, or when the first switch is turned on and the second switch is turned off to switch both switches, the both switches are turned on. A temperature control device characterized by setting a predetermined period. A gas detector comprising the temperature control device according to claim 1 for detecting the concentration of combustible gas in the atmosphere to be detected.
By driving the first switch and the second switch, the energization state of the heating resistor is set to a certain period so that the heating resistor has respective resistance values respectively corresponding to two preset temperatures. Energization control means for performing control to switch every time;
A resistance temperature detector whose resistance value changes due to a change in environmental temperature that is a temperature in the detected atmosphere;
Using the both-ends voltage of the heating resistor detected when the heating resistor is energized from the energization control means, and the environmental temperature based on the voltage difference caused by the change in the resistance value of the resistance temperature detector, Gas concentration calculating means for calculating the concentration of the combustible gas in the detected atmosphere;
A gas detection device comprising: The two set temperatures are preset to a first set temperature on the high temperature side and a second set temperature on the low temperature side among the set temperatures,
The gas concentration calculation means uses a voltage at both ends of the heating resistor detected at the first set temperature as a high temperature voltage, a voltage at both ends of the heating resistor detected at the second set temperature as a low temperature voltage, 3. The humidity in the detected atmosphere is calculated based on a ratio between the high temperature voltage and the low temperature voltage, and the concentration of the combustible gas is corrected using the humidity. The gas detection apparatus as described. The first fixed resistor and a switching resistor variable to a fixed value different in resistance value are connected in series via the first connection point, and the resistance value changes due to heat generation with the second fixed resistor. A Wheatstone bridge circuit in which a heating resistor and a second side connected in series via a second connection point are connected in parallel;
A differential amplifier circuit to which a potential difference between the potential of the first connection point and the potential of the second connection point is supplied;
The switching resistor has a configuration in which a first switching resistor having a first resistance value and a second switching resistor having a second resistance value are connected in parallel, and the connection of the first switching resistor is turned on. A first switch that turns off; a second switch that turns on and off the connection of the second switching resistor; and
A temperature control method for switching and controlling the temperature of the heating resistor to a predetermined set temperature using a temperature control device comprising:
The output of the differential amplifier circuit is applied to the Wheatstone bridge circuit so that the potential difference becomes zero, and the Wheatstone bridge circuit is controlled so as to satisfy an equilibrium condition.
When the first switch and the second switch are driven to switch the resistance values of the two switching resistors to switch the temperature of the heating resistor to a predetermined set temperature, the first switch is turned off and the first switch is turned off. When switching between both switches by turning on two switches, or when switching both switches by turning on the first switch and turning off the second switch, the switches have a predetermined period for turning on. The temperature control method characterized by controlling.

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