JP4820174B2 - Heater control circuit and thermal conductivity measuring device - Google Patents

Description

  The present invention relates to a heater control circuit and a thermal conductivity measuring device, and in particular, a technique for measuring the thermal conductivity and flow rate of a gas or liquid by measuring the amount of heat taken away from or moved by heating the heater. It is related to the field.

  Conventionally, humidity measuring devices, gas concentration measuring devices, liquid concentration measuring devices, etc. that measure the concentration of specific substances by measuring the thermal conductivity of gases and liquids are known, and gas is measured using the measured thermal conductivity. In addition, an anemometer that measures the flow of liquid and a flow rate measuring device that measures a flow rate from the measured value are known.

  The thermal conductivity is a constant in which the amount of heat that flows through the upper and lower surfaces of a predetermined cross section in an isotropic object per unit time in the normal direction is proportional to the temperature gradient in the normal direction and the cross sectional area. For example, paying attention to the fact that the thermal conductivity is related to the molecular weight of the gas, in a hygrometer using the difference in the thermal conductivity of the gas, it is caused by the difference in the amount of heat released from the heated heating resistor into the atmosphere. The humidity is obtained from the amount of change in the resistance value of the heating resistor.

  In addition, for example, in a thermosensitive type anemometer, temperature measuring resistors are arranged upstream and downstream of the heating resistor, and the heating resistor is heated upstream and downstream by a certain temperature above the fluid, and the upstream and downstream temperature measuring resistors. The temperature of each fluid is measured by the body, and the flow velocity of the fluid is obtained from this temperature difference, that is, the amount of heat transferred from upstream to downstream.

  In this way, by making the heater, which is a heating resistor, generate heat, and measuring the amount of heat taken away from the heater and the amount of heat that moves, it is possible to measure the thermal conductivity and flow of gas, etc. Technology is disclosed.

  For example, Patent Document 1 relates to a heater control method for a flow rate measuring device that measures the flow of gas by causing the heater to generate heat and measuring the amount of heat that moves from the heater, and particularly the heater temperature with respect to the ambient gas temperature. This invention relates to a heater control system that controls a constant temperature to a higher temperature. Even when the heater has deteriorated over time and its resistance value has changed, the heater always has an ambient temperature by controlling the energy (wattage) applied to the heater at a constant level. A means for increasing the heat generation temperature by a certain temperature is disclosed.

  Further, for example, in Patent Document 2, a method for measuring the moisture content (humidity) in the atmosphere, among the devices for measuring the thermal conductivity of the atmosphere, in the heater driving method of the atmosphere meter that measures the thermal conductivity of the atmosphere. In the invention, a method for reducing the energy applied to the heater by measuring the thermal conductivity of the surrounding gas at the peak temperature of the heat generation using a triangular wave current is proposed to cause the heater to generate heat.

  Further, for example, Patent Document 3 relates to a method of measuring humidity from the amount of heat taken away by the surrounding gas by heating the heater at a constant temperature using Wheatstone Blitch or the like using the characteristic that the resistance value of the heater indicates the heater temperature. In particular, in the invention relating to the temperature compensation method, there is a method for performing temperature compensation by taking the difference between the voltage generated in the heater at a low temperature and the voltage generated in the heater at a high temperature so that the heat generation temperature of the heater can be switched between a high temperature and a low temperature. It is disclosed.

Further, for example, Patent Document 4 and Patent Document 5 propose a technique for measuring the concentration by specifying the gas or liquid component using the temperature dependence of the thermal conductivity of the gas or liquid. In Patent Document 4, a gas analysis method is proposed in which a heater is controlled so that a constant temperature is maintained even when the ambient temperature changes, and the thermal conductivity of the ambient atmosphere is measured from the energy required for heat generation. By changing the temperature in multiple stages, the concentration of the gas component is determined from the difference in thermal conductivity of the surrounding gas at each temperature. Patent Document 5 describes a method for detecting components in a liquid, particularly liquefied natural gas, and the control thereof is a Wheatstone blitch configuration, and the heater heat generation temperature is changed by changing the resistance balance of the blitch with a switch. Is used.
Japanese Patent Laid-Open No. 9-306737 Japanese Patent No. 2889909 Japanese Patent No. 3533795 JP-A-8-50109 Special Table 2002-543385

  The invention of Patent Document 1 describes a heater control means for maintaining the heater heat generation temperature at a constant temperature higher than the ambient temperature even if the heater deteriorates over time, but it does not prevent the heater deterioration but has a limit. is there.

  Further, the invention of Patent Document 2 is a method in which a heater is heated using a triangular wave current, and the thermal conductivity of the surrounding gas is measured at the peak temperature of the heat generation. This method ends from the start of energization to the heater. Since the maximum value of the current applied to the heater is fixed by fixing the time until the heater is heated, the heating temperature of the heater varies depending on the ambient temperature. In such a measurement principle, an error occurs because the thermal conductivity has temperature dependence. Although it is conceivable to use this heater control method as a means for preventing the above-described heater deterioration, it is difficult to cope with this because the method for controlling the heat generation temperature of the heater is different.

  In the invention of Patent Document 3, the heat generation temperature of the heater is switched between a high temperature and a low temperature, and temperature compensation is performed based on a difference between these outputs. A thermal response delay occurs in the heater depending on the transmission speed, and the piece or circuit operates so as to apply a large current so as to achieve resistance balance, so that an overcurrent flows through the heater. In other conventional techniques, as a countermeasure against the above-described event, an overcurrent prevention method using a resistor or a capacitor is used. In this case, the time constant of the resistor and the capacitor is made sufficiently larger than the thermal time constant of the heater. This requires a long time for measurement.

  FIG. 16 shows a method of switching the heat generation temperature according to Patent Document 3. FIG. 16 is configured such that the heater can be heated effectively with a small power supply voltage, and the internal resistance of the semiconductor switch or the like when the circuit is switched with a semiconductor switch or the like having an uncertain and large internal resistance can be ignored. However, in such a configuration, an operational amplifier is required for each temperature switching, and a plurality of fixed resistors and the like that determine the heat generation temperature are also required.

  The inventions of Patent Literature 4 and Patent Literature 5 are control methods using a Wheatstone Brich circuit, and because the Wheatstone Brich balance is broken for each heater temperature to be measured, it takes time for the heater temperature to stabilize, As the heater temperature for measurement increases, the measurement time becomes longer.

  Therefore, in view of the above circumstances, the present invention reduces the thermal stress and electrical stress by minimizing the energy applied to the heater to prevent the heater from deteriorating, shortens the measurement time, and sets the heater to a predetermined value. An object of the present invention is to provide a heater control circuit or the like that controls the temperature.

In order to achieve this object, the invention according to claim 1 is a heater control circuit in which a heating resistor whose resistance value changes based on a temperature generated by energization and a resistance that the heating resistor exhibits at a predetermined temperature. A resistor having a value equivalent to the value , a temperature compensating resistor which is a heating resistor for temperature compensation connected in series with the resistor, an amplifying means for amplifying the voltage, and a voltage generated by the voltage generating means Comparison of comparing energizing means having current generating means for generating two currents with a heating resistor voltage that is a voltage generated at both ends of the heating resistor and a resistor voltage that is a voltage generated at both ends of the resistor The comparison means detects a timing at which the heating resistor voltage becomes equal to the resistor voltage and outputs a detection signal, and the energization means is generated by the current generation means. Two current supplying an electric current to the heat generating resistor and the resistor, to reset the power on the basis of the detection signal, the energization means, said temperature compensating a minute ramp current having a magnitude that the temperature compensating resistor is not exothermic The resistor and the resistor are energized, and the amplifying means is a voltage generated across the temperature compensation resistor and the resistor based on the ratio of the lamp current to the heating resistor and the minute lamp current. A certain temperature compensation resistor voltage is amplified .

  The invention described in this claim includes a heating resistor for determining a heat generation temperature, a resistor having a resistance value indicating the heat generation temperature, an energizing means for passing a current to these resistors, and a comparing means for comparing voltages generated in these resistors. It is a heater control circuit provided, and the same lamp current is energized to the resistor at the same timing by the energizing means, the time point when the voltages generated in both resistors are equalized by the comparing means, and the energization is reset, It can be controlled to achieve the target heat generation temperature using the minimum necessary energy.

  According to a second aspect of the present invention, in the heater control circuit according to the first aspect, the energizing unit generates two lamp currents having the same magnitude generated by the current generating unit and the heating resistor and the resistor. It is characterized by energizing the body.

According to a third aspect of the present invention, in the thermal conductivity measuring device, the heater control circuit according to the first or second aspect , and a control including a time measuring unit that measures a time until the detection signal is output by the comparison unit. And the comparison means outputs the detection signal to the control means, and the control means stops the time measurement by the time measuring means when the detection signal from the comparison means is input, A reset signal is output to the energization unit, and the energization unit resets energization based on a reset signal from the control unit.

According to a fourth aspect of the present invention, there is provided the thermal conductivity measuring apparatus according to the third aspect , further comprising switching means capable of freely switching a circuit operation, wherein the resistors are connected in series, and The switching means can switch between energizing one or a plurality of energies, and the comparing means, when energizing the one resistor and the plurality of resistors, the heating resistor voltage and the The timing at which the resistor voltage becomes equal to each other is detected and the detection signal is output to the control means. The control means outputs the detection signal from the comparison means when one resistor and a plurality of the resistors are energized. Each measurement result based on the detection signal is stored, and a time difference is obtained from the measurement result.

The invention according to claim 5 is the thermal conductivity measuring device according to claim 3 , further comprising switching means capable of freely switching the circuit operation, wherein the plurality of resistors are connected in parallel, and The switching means can switch which of the resistors is energized, and the comparing means is a timing at which the heating resistor voltage becomes equal to the resistor voltage when any of the resistors is energized. , And outputs the detection signal to the control means, and the control means stores the measurement results based on the detection signals from the comparison means when any of the resistors is energized, and the measurement The time difference is obtained from the result.

The invention according to claim 6 is characterized in that, in the thermal conductivity measuring device according to claim 4 or 5 , the comparing means and the amplifying means can be used in common by a plurality of the switching means.

According to a seventh aspect of the present invention, in the thermal conductivity measuring apparatus according to the sixth aspect , an offset adjusting means for adjusting an offset of the lamp current by the current generating means, and an inclination adjustment of the lamp current by the current generating means. And an inclination adjusting means for performing.

The invention according to claim 8 is the thermal conductivity measuring apparatus according to any one of claims 3 to 7 , wherein the control means is configured to measure the heat of the atmosphere based on the measured time or the obtained time difference. It is characterized by calculating conductivity.

  According to the present invention, the heater control circuit that reduces the thermal stress and electrical stress by minimizing the energy applied to the heater to prevent deterioration of the heater, shortens the measurement time, and controls the heater to a predetermined temperature. Etc. are realized.

  Hereinafter, a heater control circuit and a thermal conductivity measuring device according to an embodiment of the present invention will be described with reference to the drawings.

<Embodiment 1>
The heater control circuit of the present embodiment can reduce thermal stress and electrical stress, which are one cause of aging, and particularly relates to a heater control system that controls the heat generation temperature of the heater to a predetermined temperature.

  FIG. 1 is a block circuit diagram showing a schematic configuration of the heater control circuit of the present embodiment. The heater control circuit of the present embodiment includes a heater 11, R1 (hereinafter referred to as a fixed resistor) 12, a comparator 13, and a lamp current source 14. The lamp current source 14 includes a lamp voltage generation circuit 15 and a voltage / current conversion circuit 16. And 17.

  The heater 11 is a platinum resistor whose resistance value changes positively according to temperature. The resistance value of the fixed resistor 12 is the same as the resistance value that the heater 11 shows at a predetermined temperature. The voltage generated by the lamp voltage generation circuit 15 is converted into a lamp current by the voltage / current conversion circuits 16 and 17, and the lamp current supplied to the heater 11 and the lamp current supplied to the fixed resistor 12 have the same current value. Things are used. The comparator 13 compares the voltage generated by the heater 11 with the voltage generated by the fixed resistor 12 and outputs the comparison result.

  In the present embodiment, the lamp current is used as the energizing means for generating heat from the heater to limit the rate of temperature rise of the heater, and an equivalent lamp current is also applied to the resistor that determines the heat generation temperature of the heater at the same timing. By detecting the point where the voltage generated by the heater and the voltage generated by the resistor intersect with a comparator and resetting the lamp current, the maximum value of the heater heat generation temperature is set to the heat generation temperature determined by the resistance, and the energy applied to the heater is reduced. Yes.

  The operation of the heater control circuit of this embodiment will be described with reference to FIG. FIG. 2 shows a graph of voltage characteristics generated by the heater and R1 (fixed resistor 12), and a timing chart.

  Since the heater 11 is an element that generates heat when energized and the resistance value increases due to heat generation, the voltage generated in the heater 11 is a voltage as shown in the heater / R1 voltage characteristic graph of FIG. 2 as the current increases. It becomes a waveform and eventually crosses the voltage generated by the fixed resistor 12. The intersection is caught by the comparator 13 and the lamp current is reset by the output signal of the comparator 13.

  At this time, the input of the comparator 13 becomes indefinite, but by connecting a capacitor in parallel to the fixed resistor 12 (not shown), or by inserting a differentiation circuit in the output of the comparator 13 (not shown). The input of the comparator 13 returns to the state at the start of lamp current energization. By responding in this way, it becomes a repetitive operation as shown in the graph.

  In the series of operations described above, since the currents flowing through the heater 11 and the fixed resistor 12 are the same at the point where the voltages generated by the heater 11 and the fixed resistor 12 intersect, the resistance value of the heater 11 and the resistance value of the fixed resistor 12 are the same. Have the same resistance value. Therefore, since the resistance value indicated by the heater 11 indicates the temperature of the heater 11, the heater heat generation temperature at this intersection is a constant temperature determined by the fixed resistor 12.

<Embodiment 2>
Another embodiment of the present invention is shown in FIG. FIG. 3 is a block circuit diagram showing a schematic configuration of the heater control circuit according to the present embodiment, and represents the heater control circuit that controls the heater so that the heat generation temperature of the heater becomes a constant temperature higher than the ambient temperature. This embodiment is different from the first embodiment in that two platinum resistors having the same characteristics and the same shape are used and one is used for temperature compensation (hereinafter referred to as a temperature compensation element), and an amplifier is used. And it is different in that it is converted into a minute current by the voltage-current conversion circuit on the fixed resistance side. Since the configuration other than the above differences is the same as that of the first embodiment, description of the common points is omitted.

  The fixed resistor 12 to be compared with the heater 11 is used as the “temperature compensation element + R1”, and the lamp current energized to the “temperature compensation element + R1” is set to be a minute current (1/1 of the current flowing through the heater 11) so that the temperature compensation element 31 does not generate heat. 10). The voltage generated at “temperature compensation element + R1” is amplified (10 times) by the amplifier 32 in accordance with the ratio of the lamp current flowing through the heater 11 and the lamp current flowing through “temperature compensation element + R1”, and can be compared by the comparator 13. I am doing so.

  By configuring the circuit as described above, the heater 11 generates heat up to the temperature indicated by the resistance value of “temperature compensation element + R1”. That is, the resistance value of the temperature compensation element 31 indicates a resistance value depending on the ambient temperature when the heater 11 is not generating heat. Therefore, the heater 11 has a constant value determined by the fixed resistor 12 from the ambient temperature. It will generate heat up to a higher temperature.

  As described above, the heater control circuit according to the first embodiment and the present embodiment does not obtain heat continuously, and obtains a constant temperature or a constant temperature difference at the peak of heat generation. Energy can be reduced. Furthermore, since the temperature of the heater does not rise suddenly, deterioration due to heat shock can be suppressed, and current consumption can be reduced.

  In addition, when the heater control circuit of this embodiment is used for flow velocity measurement, the timing at which the heater heat generation temperature reaches a peak can be easily obtained from the output of the comparator. If held by a sample hold circuit or the like, measurement becomes possible. Even when the heater control circuit of the first embodiment is used for measuring the thermal conductivity of the atmosphere, the heater voltage at the time when the heater heat generation temperature reaches a peak may be held by a sample hold circuit or the like.

<Embodiment 3>
Next, another embodiment of the present invention will be described. In this embodiment, the heater driving circuit of the first or second embodiment is used to measure the time from the start of lamp current energization until the heat generation temperature of the heater reaches a predetermined temperature by using a timer of a microcomputer or the like. The voltage generated in the circuit can be obtained.

  FIG. 4 is a block circuit diagram showing a schematic configuration of the heater control circuit of the present embodiment. The circuit of FIG. 4 includes a microcomputer 41 in addition to the circuit of the first embodiment. The microcomputer 41 has a built-in external interrupt function, output port control function, and timer function, and performs lamp current reset control in the first embodiment. Since other configurations are the same as those of the first embodiment, description of common configurations is omitted.

  The operation of the heater control circuit of this embodiment will be described with reference to FIG. FIG. 5 shows a graph of a voltage characteristic generated by the heater and R1 (fixed resistor 12), and a timing chart.

  The microcomputer 41 releases the reset signal at an arbitrary timing and starts a timer. As a result, a lamp current flows through the heater 11 and the fixed resistor 12. The voltage generated by the heater 11 and the voltage generated by the fixed resistor 12 change with time as shown in the graph of the heater / R1 characteristic. Since the heater 11 is a platinum resistance element that generates heat when energized and the resistance value increases as the temperature rises due to heat generation, the voltage waveform is as shown in the graph as the current increases. Further, the voltage generated in the heater 11 intersects the voltage generated in the fixed resistor 12 as time passes as shown in the graph.

  The comparator 13 captures the point where the voltages cross and outputs a signal to the interrupt input of the microcomputer 41. In response to the interrupt, the microcomputer 41 outputs a reset signal and stops the timer.

  Since the same lamp current flows through the heater 11 and the fixed resistor 12 at the point where the voltage generated by the heater 11 and the voltage generated by the fixed resistor 12 intersect, the resistance values of the heater 11 and the fixed resistor 12 also have the same resistance value. It has become. Since the resistance value of the fixed resistor 12 is set to a resistance value when the heater is heated at a predetermined high temperature, the heater temperature has reached a predetermined temperature at this intersection.

  Thus, since the heater resistance value at the intersection is constant and the slope of the lamp current with respect to time is always constant, the value indicated by the timer of the microcomputer 41 is proportional to the heater voltage (time = current, The resistance value is fixed, so time = voltage). That is, the voltage at the time when the heater reaches a predetermined temperature (resistance value) can be measured from the timer value of the microcomputer 41.

  In this embodiment, the temperature rise rate of the heater 11 is determined by the slope of the lamp current and the ambient environment, and by using a high-performance lamp current source, the reproducibility by repeated measurement is excellent, and Since the voltage at which the heater heat generation temperature reaches a predetermined temperature can be detected by time as the heater temperature rises, repeated measurements can be performed without waiting for the heater heat generation to reach equilibrium. is there.

<Embodiment 4>
Next, another embodiment of the present invention will be described. In the present embodiment, two different temperature controls are performed using two fixed resistors, and a difference voltage at two temperatures can be obtained from two time differences measured by the timer function of the microcomputer in the third embodiment. .

  FIG. 6 is a block circuit diagram showing a schematic configuration of the heater control circuit of the present embodiment. The circuit of FIG. 6 includes an R2 (hereinafter referred to as a fixed resistor) 62 and two analog switches in addition to the circuit of the third embodiment. The fixed resistor 62 is connected in series with the fixed resistor 12, and S1 (hereinafter referred to as a switch) 63 and S2 (hereinafter referred to as a switch) 64 are turned ON / OFF in response to the output of the microcomputer 61. Since other configurations are the same as those of the third embodiment, description of common configurations is omitted.

  Only the fixed resistor 12 has a value equivalent to the resistance value that the heater exhibits at a predetermined low temperature, but by connecting the fixed resistor 62 in series, the heater has a value equivalent to the resistance value that the heater exhibits at a predetermined high temperature. In addition, the voltage generated by each resistor is switched by switches 63 and 64 so that the comparator 13 can compare the voltage generated by each fixed resistor with the voltage generated by the heater. Then, a lamp current equivalent to the lamp current passed through the heater is passed through these fixed resistors, and the voltage generated by the heater and the voltage generated by these fixed resistors are compared by the comparator 13, whereby the heater temperature is a predetermined low temperature. The difference between the voltage generated at the heater at a high temperature and the voltage generated at the heater at a low temperature can be obtained by measuring the time difference between these points and a point at which the temperature reaches a predetermined high temperature. Making it possible to seek.

  In addition, the above-described operation is performed in the process of increasing the temperature of heat generation by heating the lamp current, and there is no switching operation of the heat generation temperature for the heater, and no excessive current flows through the heater. The problem in Document 3 does not occur.

  The operation of the heater control circuit of this embodiment will be further described with reference to FIG. FIG. 7 shows a graph of a voltage characteristic generated by the heater and R1 (fixed resistor 12) and R2 (fixed resistor 62), and a timing chart.

  The microcomputer 61 releases the reset signal at an arbitrary timing, and further turns on the switch 63 and turns off the switch 64. As a result, a lamp current flows through the heater 11, the fixed resistor 12, and the fixed resistor 62. The voltage generated in the heater 11, the voltage generated in the fixed resistor 12, and the voltage generated in the fixed resistors 12 and 62 change with time as shown in the heater / R1 / R2 characteristic graph of FIG. Since the heater 11 is a platinum resistance element whose resistance value increases as the temperature rises due to heat generation, the heater 11 generates heat when energized, and has a voltage waveform as shown in the graph as the current increases.

  The voltage generated in the heater 11 crosses the voltage generated in R1 (fixed resistor 12) at t1 as time passes. Then, the comparator 13 captures the point where the voltages cross and outputs an interrupt signal to the microcomputer 61. Then, the microcomputer 61 receives the interrupt, turns off the switch 63, turns on the switch 64, and starts the timer.

  As time further elapses, the voltage generated in the heater 11 intersects with the voltage generated at “R1 (fixed resistor 12) + R2 (fixed resistor 62)” at t2. Then, the comparator 13 captures the point where the voltages cross and outputs an interrupt signal to the microcomputer. Then, the microcomputer 61 receives an interrupt, outputs a reset signal, and stops the timer.

  The heater 11, the fixed resistor 12, and the fixed resistor 62 are the same at a point t 1 where the voltage generated by the heater 11 intersects the voltage generated by the fixed resistor 12 and a point t 2 where the voltage generated by “fixed resistor 12 + fixed resistor 62” intersects. Therefore, the resistance value of the heater becomes the same resistance value as that of the fixed resistor 12 and “fixed resistor 12 + fixed resistor 62”. The resistance value of the fixed resistor 12 is set to a resistance value when the heater 11 is heated at a predetermined low temperature, and the resistance value of “fixed resistor 12 + fixed resistor 62” is a predetermined value. Since the resistance value when the heat is generated at a high temperature is set, the heater temperature is a predetermined low temperature and high temperature at these intersections.

  Since the slope of the lamp current with respect to time is always constant, the value indicated by the timer of the microcomputer is a value proportional to “heater voltage at high temperature−heater voltage at low temperature”. The timer value thus obtained can be easily converted into a voltage value or directly into the thermal conductivity of the surrounding gas by the calculation function of the microcomputer.

<Embodiment 5>
Another embodiment of the present invention is shown in FIG. FIG. 8 is a block circuit diagram showing a schematic configuration of the heater control circuit of the present embodiment, and shows a heater control circuit in which two fixed resistors provided in series in the fourth embodiment are connected in parallel. In FIG. 8, the resistance value of the fixed resistor 82 is equivalent to “fixed resistor 12 + fixed resistor 62” in FIG.

  In the present embodiment, since the lamp current is driven as in the fourth embodiment, even if a switch for switching the current is inserted, the same operation as the circuit of the fourth embodiment is possible without being affected by the impedance of the switch.

<Embodiment 6>
Next, another embodiment of the present invention will be described. In this embodiment, a plurality of semiconductor switches or the like are used so that a comparison detector such as a comparator can be used in common, and an inclination adjustment circuit and an offset adjustment circuit are provided so that inclination adjustment and offset adjustment can be performed.

  FIG. 9 is a block circuit diagram showing a schematic configuration of the heater control circuit of the present embodiment. The circuit of FIG. 9 is obtained by adding a lamp current offset adjusting circuit and a slope adjusting circuit to the circuit of FIG. 6 and further enabling temperature measurement with a heater. A DA converter with a built-in microcomputer is used to control the adjustment circuit. Further, in the voltage / current circuit on the fixed resistance side as in the second embodiment, the voltage is converted into a minute current and amplified by an amplifier so as to be comparable with the voltage on the heater side. In this circuit, a plurality of operation states can be realized by a combination of switches, and four typical states will be described below.

  10A and 10B are diagrams showing the thermal conductivity measurement state, where FIG. 10A shows the control state, and FIG. 10B shows the voltage characteristics of the heater and fixed resistance. The difference between the circuit of FIG. 9 and the circuit of FIG. 6 is that a weak lamp current source is required to enable temperature measurement, so that R1 (fixed resistor 12) and R2 (fixed resistor 62) are different. The current flowing is set to 1/10 of the current flowing through the heater 11 and amplified using a 10-fold amplifier so that the voltage generated by the fixed resistor 12 and the fixed resistor 62 can be compared with the voltage generated by the heater 11. Is a point.

  First, the microcomputer 91 cancels the reset signal at an arbitrary timing, turns on the voltage-current conversion circuits 16 and 33, and switches S1 (switch 101), S4 (switch 104), S7 (switch 107), and S10 (switch 110). Only S13 (switch 113) is turned ON. As a result, a lamp current flows through the heater 11, the fixed resistor 12, and the fixed resistor 62, and the voltage generated in the heater, the voltage generated in the fixed resistor 12, and the voltage generated in the fixed resistor 62 are as shown in the graph of FIG. Over time.

  The voltage generated by the heater 11 crosses the voltage generated by the fixed resistor 12 over time. Then, the comparator 13 captures the point where the voltages intersect and outputs an interrupt signal to the microcomputer 91. The microcomputer 91 receives the interrupt, turns off the switch 107, turns on the switch 106, and starts a timer.

  When the time further elapses, the voltage generated in the heater 11 crosses the voltage generated by the “fixed resistor 12 + fixed resistor 62”. The comparator 32 captures the point where the voltages intersect and outputs an interrupt signal to the microcomputer 91. The microcomputer 91 receives the interrupt, outputs a reset signal, and stops the timer.

  The timer value thus obtained can be directly converted into the thermal conductivity of the surrounding gas using the calculation function of the microcomputer as in the fourth embodiment.

  11A and 11B are diagrams showing the temperature measurement state, where FIG. 11A shows the control state, and FIG. 11B shows the relationship between the reference power supply voltage and the voltage generated by the heater. In FIG. 11, the switch is switched so that a lamp current of 1/10 flows through the heater 11.

  That is, the microcomputer 91 releases the reset signal at an arbitrary timing, turns on the voltage-current conversion circuits 16 and 33, and performs S3 (switch 103), S5 (switch 105), S9 (switch 109), and S11 (switch 111). ) Only ON. As a result, a 1/10 lamp current flows through the heater 11, but at a 1/10 lamp current, the heater 11 hardly generates heat, so the resistance value of the heater 11 depends on the ambient temperature and is generated in the heater 11. As shown in the graph of FIG. 11B, the voltage shows a waveform that monotonously increases as the lamp current increases.

  Further, since the lamp current is set to 1/10, the voltage generated in the heater 11 is also reduced to 1/10. Therefore, amplification is performed by the amplifier 32 of 10 times used at the time of measuring the thermal conductivity. The comparator 13 compares the voltage thus amplified with the voltage of the reference power supply 94, and outputs an interrupt signal to the microcomputer 91 at the point where the voltage of the heater 11 intersects the voltage of the reference power supply.

  The microcomputer 91 measures the ambient temperature by obtaining the resistance value of the heater by measuring the time from the start of energization of the lamp current due to the release of the reset signal to the input of the interrupt signal from the comparator 13 (time = Since it is a current value and the voltage value of the reference power source 94 is fixed, it is obtained by (voltage value of reference power source / time) × coefficient).

  12A and 12B are diagrams showing an offset adjustment state, where FIG. 12A shows a control state, FIG. 12B shows a timing chart, and FIG. 12C shows a flowchart of adjustment control. When the lamp current is in the reset state, the voltage generated at “R1 (fixed resistor 12) + R2 (fixed resistor 62)” is compared with the GND level by the comparator 13, the microcomputer 91 monitors the output of the comparator 13, and the microcomputer 91 It is adjusted by the DA converter.

  As shown in FIG. 12A, when the microcomputer 91 cancels the reset signal and turns on the voltage-current conversion circuit 16 at an arbitrary timing, S2 (switch 102), S8 (switch 108), and S12 (switch Only 112) is turned ON. When the voltage-current conversion circuit 33 is turned on, only S4 (switch 104), S6 (switch 106), S8 (switch 108), and S11 (switch 111) are turned on.

  Further, offset adjustment control performed by the microcomputer 91 will be described with reference to FIG. First, three types of variables n, m, and a are set to 0 (step S101). As will be described later, n represents a subtraction count for DA converter data, m represents an addition count, and a represents a count when n and m are 1 or more.

  Next, the output of the comparator 13 is determined. When the output is high (step S102 / YES), 1 is subtracted from the DA converter data, so that n = n + 1 (step s103). When the output is low (step S102 / NO) Since 1 is added to the DA converter data, m = m + 1 is counted (step s103).

  Next, if n ≧ 1 and m ≧ 1 (step S105 / YES), a = a + 1 is counted, and n and m are set to 0 (step s106). If n ≧ 1 and m ≧ 1 are not satisfied (step S105 / NO), the process returns to the output determination of the comparator 13 (step S102). If a ≧ 5 (step S107 / YES), the process ends. If a <5 (step S107 / NO), the process returns to the output determination of the comparator 13 (step S102).

  In the above case, since the output voltage range of the DA converter may be a range in which the circuit offset fluctuates, narrowing the output voltage range of the DA converter can sufficiently utilize even the one with poor accuracy. Even if the output of the DA converter changes due to the temperature change of the circuit, it can be used without being influenced by the temperature dependence of the DA converter by performing offset adjustment periodically.

  13A and 13B are diagrams showing the tilt adjustment state, where FIG. 13A shows a control state, FIG. 13B shows a relationship between a reference power supply voltage and a voltage generated by a fixed resistor, and FIG. 13C shows a flowchart of adjustment control. The lamp current is caused to flow through “R1 (fixed resistor 12) + R2 (fixed resistor 62)”, and an intersection between the voltage generated in these fixed resistors and the voltage of the reference power supply is detected by the comparator 13, and the microcomputer 91 is detected. Output an interrupt signal. The microcomputer 91 calculates the slope of the lamp current by measuring the time from the start of energization of the lamp current until the interrupt signal is input from the comparator 13, and compares it with a predetermined slope to meet the error. The correction value is output from the DA converter and adjusted again. Complete correction can be performed by repeating this operation a plurality of times.

  As shown in FIG. 13A, when the microcomputer 91 cancels the reset signal and turns on the voltage-current conversion circuit 16 at an arbitrary timing, S2 (switch 102), S9 (switch 109), and S12 (switch Only 112) is turned ON. When the voltage-current conversion circuit 33 is turned on, only S4 (switch 104), S6 (switch 106), S9 (switch 109) and S11 (switch 111) are turned on.

  Further, the tilt adjustment control performed by the microcomputer 91 will be described with reference to FIG. First, after setting the data value of the DA converter to 7FH and the counter to 0, the ON / OFF control is turned on (step S201) and the external interrupt is permitted (step S202).

  Next, when an interruption occurs (step S203), the interruption is prohibited and the ON / OFF control is turned off (step S204). When “counter value−reference value” becomes 0 (step S205 / YES), the DA value is determined and the process ends (step S206). On the other hand, if “counter value−reference value” is not 0 (step S205 / NO), the DA setting value is obtained from “counter value−reference value” (step S207), for example, DA is set to xxF, and the counter is set. It is set to 0, ON / OFF control is turned on (step S208), and external interrupt permission is performed (step S209).

  It should be noted that the above-described adjustment can be fully utilized even by a DA converter whose accuracy is not so good for the same reason as the offset adjustment state described above.

  As described above, in the present embodiment, the offset and inclination of the lamp current can be easily corrected by freely inserting a semiconductor switch or the like in the circuit, and the number of parts required for accuracy is reduced, and the measurement accuracy is reduced. It is possible to increase. Furthermore, the temperature can be measured with a heater, and it can be used for another purpose by changing the combination of switches in the control state described above. For example, using the offset adjustment state shown in FIG. 12, the heater resistance value when the lamp current is in the reset state is adjusted by the DA converter so as to balance with the fixed resistor 12, and the heater temperature in the reset state is changed to the low temperature heating state. Alternatively, the measurement resolution can be changed by intentionally changing the inclination using the lamp current inclination adjustment state shown in FIG.

<Embodiment 7>
Next, another embodiment of the present invention will be described. In the present embodiment, a plurality of fixed resistors to be compared with the heater are further used in the circuit of the fourth embodiment, so that the heater voltage at a plurality of temperatures can be measured by supplying a single lamp current.

  FIG. 14 is a block circuit diagram showing a schematic configuration of the heater control circuit of the present embodiment. N fixed resistors are connected in series from R1 to Rn, and a plurality of analog switches that are turned ON / OFF by the microcomputer 61 are provided. Other configurations are the same as those of the fourth embodiment. FIG. 14 is based on the circuit of FIG. 6, but it is of course possible to configure based on FIG. 9, and in that case, higher performance can be achieved.

  The operation of the heater control circuit of this embodiment will be further described with reference to FIG. FIG. 15 shows a graph of voltage characteristics generated by the heater and the fixed resistance, and a timing chart.

  The activation of this circuit is started by canceling the reset signal by the microcomputer 201, energizing the lamp 11 with the heater 11 and the fixed resistors (R1 to Rn), and turning on the switch 211 (at this stage, other circuits are activated). The switch is OFF). The energization of the lamp current is started, and as the current increases with time, the voltage generated in the heater 11 and the voltage generated in the fixed resistor 12 intersect at t1, and an interrupt signal is generated from the comparator 13 to the microcomputer 201. In response to this, the microcomputer 201 starts a timer to turn off the switch 211 and turn on the switch 212.

  As the time further elapses, the current increases, and the voltage generated by the heater 11 and the voltage generated by “R1 (fixed resistor 12) + R2 (fixed resistor 202)” intersect at t2, and the comparator 13 sends the voltage to the microcomputer 201. An interrupt signal is generated. In response to this, the microcomputer 201 stores the timer value in the memory, turns off the switch 212, and turns on the switch 213.

  By repeating such an operation, the voltage finally generated at R1 (fixed resistor 12) + R2 (fixed resistor 202) +... + Rn (fixed resistor 203) and the voltage generated at the heater 11 intersect at tn. 13 generates an interrupt signal to the microcomputer 201. After the timer value is stored in the memory, the microcomputer 201 stops the timer by turning off the switch 213 and stops the lamp current by setting the reset signal.

  Since the numerical value stored in the memory is a current value when the heater temperature reaches a predetermined temperature (resistance value), it can be easily converted into a voltage value. As described above, in this embodiment, the heater voltage at a plurality of temperatures can be measured by supplying the lamp current once, and it is not necessary to wait for the heater temperature to stabilize every time the temperature is switched. As a result, AD conversion can be performed, so that unnecessary time is not required for measurement. Furthermore, since a plurality of temperatures can be detected by a single comparator, it is not necessary to consider offset variations of the comparator.

  According to the above embodiment, it is possible to reduce the electric power applied to the heater, thereby reducing electrical and thermal stress.

  Moreover, according to said embodiment, it becomes possible to measure the thermal conductivity of surrounding gas by measuring the voltage when a heater heat | fever-generates to predetermined temperature with time.

  Further, according to the above-described embodiment, it is possible to perform measurement at high speed without flowing an overcurrent to the heater that is generated when the heating temperature of the heater is switched.

  In addition, according to the above-described embodiment, it is possible to easily add a function and to reduce the number of parts and to increase the measurement accuracy by freely switching on the switch.

  In addition, according to the above-described embodiment, the heater voltage at a plurality of heater temperatures can be measured by energizing the lamp current once, and it is possible to cope with the discrimination of a plurality of gases from the temperature dependence of the thermal conductivity. It becomes possible.

  The above-described embodiment is a preferred embodiment of the present invention, and the scope of the present invention is not limited to the above-described embodiment alone, and various modifications are made without departing from the gist of the present invention. Implementation is possible.

It is a block circuit diagram of a heater control circuit according to an embodiment of the present invention. It is explanatory drawing about operation | movement of the heater control circuit which concerns on embodiment of this invention. It is a block circuit diagram of a heater control circuit according to an embodiment of the present invention. It is a block circuit diagram of a heater control circuit according to an embodiment of the present invention. It is explanatory drawing about operation | movement of the heater control circuit which concerns on embodiment of this invention. It is a block circuit diagram of a heater control circuit according to an embodiment of the present invention. It is explanatory drawing about operation | movement of the heater control circuit which concerns on embodiment of this invention. It is a block circuit diagram of a heater control circuit according to an embodiment of the present invention. It is a block circuit diagram of a heater control circuit according to an embodiment of the present invention. It is explanatory drawing about operation | movement of the heater control circuit which concerns on embodiment of this invention. It is explanatory drawing about operation | movement of the heater control circuit which concerns on embodiment of this invention. It is explanatory drawing about operation | movement of the heater control circuit which concerns on embodiment of this invention. It is explanatory drawing about operation | movement of the heater control circuit which concerns on embodiment of this invention. It is a block circuit diagram of a heater control circuit according to an embodiment of the present invention. It is explanatory drawing about operation | movement of the heater control circuit which concerns on embodiment of this invention. It is a block circuit diagram of the heater control circuit in a prior art.

Explanation of symbols

11 Heater 12 Fixed resistance (R1)
13, 83, 84 Comparator 14 Lamp current source 15 Lamp voltage generation circuit 16, 17 Voltage current conversion circuit 31 Temperature compensation element 32 Amplifier 33 Voltage current conversion circuit (× 1/10)
41, 61, 81, 91, 201 Microcomputer 62, 82, 202 Fixed resistor (R2)
63, 101, 211 switch (S1)
64, 102, 212 switch (S2)
92 Inclination adjustment circuit 93 Offset adjustment circuit 94 Reference power supply 103 Switch (S3)
104 switch (S4)
105 switch (S5)
106 switch (S6)
107 switch (S7)
108 switch (S8)
109 switch (S9)
110 switch (S10)
111 switch (S11)
112 switch (S12)
113 switch (S13)
203 Fixed resistance (Rn)
213 Switch (Sn)
300 operational amplifier circuit 310 differential amplifier 320 switch 330 resistor 340 operational amplifier circuit

Claims (8)

A heating resistor whose resistance value changes based on the temperature generated by energization,
A resistor having a value equivalent to the resistance value of the heating resistor at a predetermined temperature;
A temperature compensating resistor which is a heating resistor for temperature compensation connected in series with the resistor;
Amplifying means for amplifying the voltage;
An energizing means including a current generating means for generating two currents based on a voltage generated by the voltage generating means;
Comparing means for comparing a heating resistor voltage which is a voltage generated at both ends of the heating resistor and a resistor voltage which is a voltage generated at both ends of the resistor;
The comparison unit detects a timing at which the heating resistor voltage and the resistor voltage are equal, and outputs a detection signal;
The energization unit energizes the heating resistor and the resistor with two currents generated by the current generation unit, resets energization based on the detection signal ,
The energizing means energizes the temperature compensating resistor and the resistor with a minute lamp current having a size that does not generate heat.
The amplifying unit amplifies a temperature compensation resistor voltage, which is a voltage generated at both ends of the temperature compensation resistor and the resistor, based on a ratio of a lamp current to the heating resistor and the minute lamp current. A heater control circuit characterized by the above.   2. The heater control circuit according to claim 1, wherein the energizing unit energizes the heating resistor and the resistor with two lamp currents having the same magnitude generated by the current generating unit. The heater control circuit according to claim 1 or 2 ,
Control means comprising time measuring means for measuring the time until the output of the detection signal by the comparison means,
The comparison means outputs the detection signal to the control means,
The control means stops time measurement by the time measuring means when a detection signal from the comparison means is input, and outputs a reset signal to the energization means,
The thermal conductivity measuring device, wherein the energization means resets energization based on a reset signal from the control means. Having a switching means capable of freely switching the circuit operation;
A plurality of the resistors are connected in series, and can be switched by the switching means to energize one or to energize one,
The comparing means detects the timing at which the heating resistor voltage and the resistor voltage are equal when one resistor and a plurality of the resistors are energized, and sends the detection signal to the control means. Output,
The control means stores a measurement result based on a detection signal from the comparison means when one resistor and a plurality of the resistors are energized, and obtains a time difference from the measurement result. Item 4. The thermal conductivity measuring device according to Item 3 . Having a switching means capable of freely switching the circuit operation;
The resistors are connected in parallel, and can be switched by the switching means to which of the resistors is energized,
The comparison means detects the timing at which the heating resistor voltage and the resistor voltage are equal when any of the resistors is energized, and outputs the detection signal to the control means,
Wherein said control means stores a detection signal to based measurement result from said comparison means when also energized in any of the resistors respectively, according to claim 3, characterized in that determining the time difference from the measurement result Thermal conductivity measuring device. The thermal conductivity measuring apparatus according to claim 4 or 5 , wherein the comparing means and the amplifying means can be used in common by a plurality of the switching means. Offset adjusting means for adjusting the offset of the lamp current by the current generating means;
The thermal conductivity measuring device according to claim 6 , further comprising an inclination adjusting unit that adjusts an inclination of a lamp current by the current generating unit. The thermal conductivity measuring device according to any one of claims 3 to 7 , wherein the control means calculates the thermal conductivity of the atmosphere based on the measured time or the obtained time difference.

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