Gas sensor module

Abstract

To provide a gas sensor module capable of reducing a load applied to a power source.SOLUTION: A gas sensor module 100 includes: an infrared light emitting diode 10 for emitting infrared light according to a drive current; a quantum infrared sensor 20 for receiving infrared light that has passed through gas to be detected; a drive circuit 30 for outputting a drive current to the infrared light emitting diode 10; a charging circuit 50 that is connected to a power source and outputs a charging current smaller in amount of current than the drive current; and a capacitor 40 that is charged by being supplied with the charging current from the charging circuit 50 and discharges by supplying the drive current to the drive circuit 30.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a gas sensor module.

Background Art

[0002] Conventionally, in an incandescent lamp used for a CO2 gas sensor, a driving method for a light source for a CO2 gas sensor that controls the voltage of the incandescent lamp so that the filament resistance value in the lit state becomes constant is known (see, for example, Patent Document 1).

[0003] In recent years, a non-dispersive infrared absorption type (NDIR: Non-Dispersive Infrared) gas sensor that includes a light emitting unit that emits infrared rays and a light receiving unit that receives infrared rays that have passed through a detection target gas (for example, CO2 gas) and detects the concentration of the gas using the infrared absorption characteristics of the gas has been developed.

Prior Art Documents

Non-Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Compared with other environmental sensors such as a temperature and humidity sensor and a pressure sensor, a non-dispersive infrared absorption type gas sensor has an extremely large drive current (peak current). For this reason, in a conventional gas sensor module 100A including a light emitting unit 10A such as a tungsten lamp (incandescent lamp) or a MEMS heater and a light receiving unit 20A such as a pyroelectric sensor or a thermopile as shown in FIG. 7, there has been a problem that an excessive load is applied to the power supply 60A.

[0006] In view of such circumstances, an object of the present disclosure is to provide a gas sensor module capable of reducing the load applied to the power supply. [Means for solving the problem]

[0007] A gas sensor module according to one embodiment is characterized by comprising: an infrared light-emitting diode that emits infrared light in accordance with a drive current; a quantum infrared sensor that receives infrared light transmitted through a gas to be detected; a drive circuit that outputs the drive current to the infrared light-emitting diode; a charging circuit connected to a power supply and outputting a charging current with a current amount smaller than the drive current; and a capacitor that is charged by the charging current supplied from the charging circuit and discharged by the drive current supplied to the drive circuit. [Effects of the Invention]

[0008] According to this disclosure, it is possible to provide a gas sensor module that can reduce the load on the power supply. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows an example of the configuration of a gas sensor module according to this embodiment. [Figure 2A] This figure shows an example of the response of an infrared light-emitting diode according to this embodiment. [Figure 2B] This figure shows an example of the response of a conventional light-emitting unit. [Figure 2C] This figure shows an example of the response of a conventional light-emitting unit. [Figure 3A] This figure shows an example of the sensitivity of a quantum infrared sensor according to this embodiment and the sensitivity of a conventional light receiving unit. [Figure 3B] This figure shows an example of the noise equivalent power of a quantum infrared sensor according to this embodiment and the noise equivalent power of a conventional light receiving unit. [Figure 4] This figure shows an example of the relationship between the voltage drop in the power supply due to capacitor discharge and the capacitance of the capacitor. [Figure 5A] This figure illustrates the gas sensor module according to this embodiment. [Figure 5B]This figure illustrates the gas sensor module according to this embodiment. [Figure 5C] This figure illustrates the gas sensor module according to this embodiment. [Figure 6] This is a diagram illustrating a conventional gas sensor module. [Figure 7] This diagram shows an example of the configuration of a conventional gas sensor module. [Modes for carrying out the invention]

[0010] The embodiments will be described in detail below with reference to the drawings.

[0011] An example of the configuration of the gas sensor module 100 according to this embodiment will be described with reference to Figures 1 to 4.

[0012] As shown in Figure 1, the gas sensor module 100 comprises an infrared light-emitting diode 10, a quantum infrared sensor 20, a drive circuit 30, a capacitor 40, a charging circuit 50, a power supply 60, and an amplification circuit / signal processing circuit 70.

[0013] The infrared light-emitting diode 10 receives a drive current I supplied from the drive circuit 30. drive It emits infrared light accordingly. The infrared light-emitting diode 10 is used as a light source for sensing a target gas (e.g., CO2 gas) that has infrared absorption characteristics. Preferably, the infrared light-emitting diode 10 emits light in the wavelength range of 2.0 μm to 12.0 μm.

[0014] The infrared light-emitting diode 10 is preferably configured as a light source with good responsiveness.

[0015] Here, referring to FIGS. 2A to 2C, the responsiveness of the infrared light emitting diode 10 according to the present embodiment and the responsiveness of the conventional light emitting unit will be described. FIG. 2A is a diagram showing an example of the responsiveness of an infrared light emitting diode. FIG. 2B is a diagram showing an example of the responsiveness of a tungsten lamp. FIG. 2C is a diagram showing an example of the responsiveness of a MEMS (Micro Electro Mechanical Systems) heater. Here, a quantum type infrared sensor with good responsiveness is used for the light receiving unit so that a detection signal depending on the responsiveness of each light emitting unit can be obtained.

[0016] In FIG. 2A, graph 201 shows the drive voltage of the infrared light emitting diode 10. Graph 202 shows the drive current of the infrared light emitting diode 10. Graph 203 shows the detection signal of the light receiving unit.

[0017] In FIGS. 2B and 2C, graph 201 shows the drive voltage of the conventional light emitting unit. Graph 202 shows the drive current of the conventional light emitting unit. Graph 203 shows the detection signal of the light receiving unit.

[0018] From graph 203 in FIG. 2A, it can be seen that when using an infrared light emitting diode, the time constant of the detection signal is about several μs (<< ms). From graph 203 in FIG. 2B, it can be seen that when using a tungsten lamp, the time constant of the detection signal is about 50 ms. From graph 203 in FIG. 2C, it can be seen that when using a MEMS heater, the time constant of the detection signal is about 30 ms.

[0019] Furthermore, from graphs 201, 202, and 203 in Figure 2A, it can be seen that the time from supplying drive current to the infrared light-emitting diode until the detection signal reaches its peak value is very short, and the peak is shown immediately after the start of drive current supply. From graphs 201, 202, and 203 in Figure 2B, it can be seen that the time from supplying drive current to the tungsten lamp until the detection signal reaches its peak value is approximately 100 ms or more. From graphs 201, 202, and 203 in Figure 2C, it can be seen that the time from supplying drive current to the MEMS heater until the detection signal reaches its peak value is approximately 100 ms or more.

[0020] Figures 2A to 2C show that infrared light-emitting diodes (LEDs) have significantly better responsiveness compared to tungsten lamps or MEMS heaters. Therefore, it is suggested that infrared LEDs can achieve extremely short operating times per cycle compared to tungsten lamps or MEMS heaters. For example, the operating time can be reduced to less than 1 ms. It can be shortened even further to around 10 μs to 100 μs. Furthermore, the on-duty ratio of the drive current (the ratio of the time the drive current is supplied to the drive cycle) can also be reduced, for example to less than 10%. This reduces the load on the power supply while achieving low power consumption as a gas sensor module. This is because, for example, with visible light LEDs, the amount of light emitted itself is important, but in the case of gas sensor modules, it is sufficient to drive for the required signal-to-noise ratio, and since the monitoring period for gas concentration is generally sufficient in seconds, a relatively long operating cycle can be adopted.

[0021] The quantum infrared sensor 20 receives infrared light that has passed through the target gas. The quantum infrared sensor 20 detects the amount of infrared light absorbed by the target gas, which has infrared absorption characteristics, according to the amount of infrared light received, and outputs a detection signal indicating the concentration of the target gas to the amplification circuit / signal processing circuit 70. The higher the concentration of the target gas, the smaller the amount of infrared light received by the quantum infrared sensor 20. The lower the concentration of the target gas, the larger the amount of infrared light received by the quantum infrared sensor 20. The distance between the quantum infrared sensor 20 and the infrared light-emitting diode 10 is preferably about 20 mm, but is not limited to this.

[0022] The gas to be detected is preferably a gas species that has absorption characteristics for light in the wavelength range of 2.0 μm to 12.0 μm. Examples include, but are not limited to, CO2, CO, CH4, H2O, NO, C2H5OH, C3H8, NH3, and CH2O.

[0023] The quantum infrared sensor 20 may further include an optical filter that has the function of transmitting light of certain wavelengths. An example of an optical filter is a bandpass filter that transmits light in the absorption wavelength band of the gas to be detected. For example, when detecting carbon dioxide, a bandpass filter that selectively transmits light around 4.3 μm can be used.

[0024] It is preferable that the quantum infrared sensor 20 is mounted on the same substrate as the infrared light-emitting diode 10. By mounting the quantum infrared sensor 20 and the infrared light-emitting diode 10 on the same substrate, it is not necessary to prepare separate substrates, thus reducing manufacturing costs. Furthermore, mounting the quantum infrared sensor 20 and the infrared light-emitting diode 10 on the same substrate improves detection accuracy.

[0025] The quantum infrared sensor 20 is preferably composed of elements that have high sensitivity and low noise. Examples of quantum infrared sensors include photocells, photodiodes, and phototransistors.

[0026] Here, with reference to Figures 3A and 3B, the sensitivity and noise equivalent power of the quantum infrared sensor 20 according to this embodiment, as well as the sensitivity and noise equivalent power of a conventional light receiving unit, will be described. Figure 3A is a diagram showing an example of the relationship between frequency and sensitivity. The horizontal axis is frequency [Hz], and the vertical axis is sensitivity [V]. rms / W rms Figure 3B shows an example of the relationship between frequency and noise equivalent power. The horizontal axis is frequency [Hz], and the vertical axis is noise equivalent power [W]. rms It is / rtHz].

[0027] Graph 301A in Figure 3A shows the sensitivity of the quantum infrared sensor. Graph 302A in Figure 3A shows the sensitivity of the thermopile. Graph 303A in Figure 3A shows the sensitivity of the pyroelectric sensor.

[0028] Graph 301B in Figure 3B shows the noise equivalent power of a quantum infrared sensor. Graph 302B in Figure 3B shows the noise equivalent power of a thermopile. Graph 303B in Figure 3B shows the noise equivalent power of a pyroelectric sensor.

[0029] From graph 301A in Figure 3A, it can be seen that the sensitivity of quantum infrared sensors is generally high and remains almost constant even when the frequency changes. From graph 302A in Figure 3A, it can be seen that the sensitivity of thermopiles is generally low and remains almost constant up to a frequency of 10 Hz, but decreases sharply above 10 Hz. From graph 303A in Figure 3A, it can be seen that the sensitivity of pyroelectric sensors decreases as the frequency increases.

[0030] From graph 301B in Figure 3B, it can be seen that the noise equivalent power of the quantum infrared sensor is generally low and remains almost constant even as the frequency changes. From graph 302B in Figure 3B, it can be seen that the noise equivalent power of the thermopile is generally high and remains almost constant up to a frequency of 10 Hz, but increases sharply above 10 Hz. From graph 303B in Figure 3B, it can be seen that the noise equivalent power of the pyroelectric sensor is generally high and increases as the frequency increases.

[0031] Figures 3A and 3B show that the quantum infrared sensor has higher sensitivity and stability compared to thermopile or pyroelectric sensors. Furthermore, the quantum infrared sensor exhibits lower noise and greater stability compared to thermopile or pyroelectric sensors.

[0032] Therefore, it is suggested that when an infrared light-emitting diode (LED) is combined with a quantum-type infrared sensor, the operating time per cycle of the infrared light-emitting diode 10 can be made extremely short compared to when a tungsten lamp or MEMS heater is combined with a thermopile or pyroelectric sensor. For example, the operating time can be reduced to 1 ms or less.

[0033] From the viewpoint of sufficiently charging the capacitor 40, it is preferable that the product of the charging current and the charging time is greater than or equal to the product of the driving current and the driving time.

[0034] The drive circuit 30 is provided between the infrared light-emitting diode 10 and the capacitor 40. The drive circuit 30 is connected to the capacitor 40 via a switch SW2, and is also connected to the infrared light-emitting diode 10. When the capacitor 40 discharges, the drive circuit 30 generates a drive current I from the capacitor 40 for the infrared light-emitting diode 10. drive The drive circuit 30 then supplies the drive current I to the infrared light-emitting diode 10. drive It supplies the drive current I of the infrared light-emitting diode 10. drive The current is preferably around 100mA. The drive current I of the infrared light-emitting diode 10. driveThe larger it is, the greater the emission amount of the infrared light-emitting diode 10, and the better the signal-to-noise ratio can be made.

[0035] The capacitor 40 is provided between the charging circuit 50 and the drive circuit 30. The capacitor 40 is connected to the charging circuit 50 via the switch SW1, and is also connected to the drive circuit 30 via the switch SW2. When the switch SW1 is turned on, the capacitor 40 is charged by the charging circuit 50, and the capacitor voltage of the capacitor 40 rises. Between the power supply 60 and the capacitor 40, there is a charging current I of the capacitor 40 charge flowing. When the switch SW1 is turned off, there is no charging current I of the capacitor 40 flowing between the power supply 60 and the capacitor 40 charge When the switch SW2 is turned on, the capacitor 40 discharges by supplying the drive current I of the infrared light-emitting diode 10 to the drive circuit 30, and the capacitor voltage of the capacitor 40 decreases. Between the capacitor 40 and the infrared light-emitting diode 10, there is a drive current I of the infrared light-emitting diode 10 drive flowing. When the switch SW2 is turned off, there is no drive current I of the infrared light-emitting diode 10 flowing between the capacitor 40 and the infrared light-emitting diode 10 drive It should be noted that the switch SW1 and the switch SW2 are not turned on at the same time. When the switch SW1 is on, the switch SW2 is off, and when the switch SW2 is on, the switch SW1 is off. drive When the switch SW2 is turned off, there is no drive current I of the infrared light-emitting diode 10 flowing between the capacitor 40 and the infrared light-emitting diode 10 [[ID=I16]]

[0036] The charging current I of the capacitor 40 charge is a current with a smaller current amount than the drive current I of the infrared light-emitting diode 10 drive From the viewpoints of reducing power consumption and improving measurement accuracy, the charging current I charge is preferably a current with an averaged drive current. The charging current I of the capacitor 40 charge is preferably about 1 / 100 times the drive current I of the infrared light-emitting diode 10 drive For example, when the detection period of the non-dispersive infrared absorption type gas sensor is 10 s, the drive current I of the infrared light-emitting diode 10 driveThis is the current that instantaneously flows between the capacitor 40 and the infrared light-emitting diode 10 at 100mA for 0.1ms, and is the charging current I of the capacitor 40. charge This is the current that flows periodically between the power supply 60 and the capacitor 40 at a rate of 1.01mA for 9.9s.

[0037] The driving current I of the infrared light-emitting diode 10 is supplied from the charging circuit 50 to the capacitor 40. drive The charging current I of capacitor 40 is smaller than that of capacitor 40. charge When power is supplied, the capacitor 40 is charged, and the drive current I of the infrared light-emitting diode 10 is supplied from the capacitor 40 to the drive circuit 30. drive The supply of current causes the capacitor 40 to discharge. As a result, in the gas sensor module 100, the drive circuit 30 directly receives the drive current I of the infrared light-emitting diode 10 from the power supply 60. drive Since it is not necessary to remove the power supply, the load on the power supply 60 can be significantly reduced. In other words, when the power supply 60 and the drive circuit 30 are connected via the charging circuit 50, switch SW1, capacitor 40, and switch SW2, as in the gas sensor module 100 according to this embodiment, the load on the power supply 60 can be significantly reduced compared to when the power supply 60A and the drive circuit 30A are directly connected, as in the conventional gas sensor module 100A (see Figure 7). Furthermore, the amount of light emitted by the infrared light-emitting diode 10 can be maintained at a level comparable to that of the light-emitting part 10A of a tungsten lamp or MEMS heater.

[0038] The capacitor 40 is preferably composed of an element with low capacitance, and is preferably a multilayer ceramic capacitor from the viewpoint of size, cost, and leakage current. The capacitance of the capacitor 40 is preferably 1 mF or less.

[0039] Now, referring to Figure 4, we will explain the relationship between the voltage drop caused by capacitor discharge and the capacitance of the capacitor. The horizontal axis represents the voltage drop ΔV [mV], and the vertical axis represents the capacitance C of the capacitor. bulk [F]

[0040] Graph 401 in Figure 4 shows the capacitor capacity when an infrared light-emitting diode (LED) is used in the gas sensor module, i.e., when the operating time per cycle of the infrared LED is 100 μs. Graph 402 in Figure 4 shows the capacitor capacity when a tungsten lamp or MEMS heater is used in the gas sensor module, i.e., when the operating time per cycle of the tungsten lamp or MEMS heater is 100 ms. In Figure 4, the operating current for the infrared LED and the operating current for the tungsten lamp or MEMS heater are assumed to be 100 mA in common.

[0041] From graph 401 in Figure 4, the larger the voltage drop ΔV, the greater the capacitance C of the capacitor. bulk It can be seen that it becomes smaller. For example, when the voltage drop ΔV is 1mV, the capacitance C of the capacitor bulk If the capacitance is 10mF and the voltage drop ΔV is 100mV, then the capacitance C of the capacitor is... bulk It can be seen that this is 100μF.

[0042] From graph 402 in Figure 4, the larger the voltage drop ΔV, the greater the capacitance C of the capacitor. bulk It can be seen that it becomes smaller. For example, when the voltage drop ΔV is 1mV, the capacitance C of the capacitor bulk If the capacitance is 10F and the voltage drop ΔV is 100mV, then the capacitance C is... bulk It can be seen that this is 100mF.

[0043] From Figure 4, the capacitance of the capacitor increases as the allowable voltage drop ΔV increases. bulk It can be seen that the capacitance becomes smaller. It is also proportional to the operating time per cycle of the infrared light-emitting diode. Therefore, it is suggested that the capacitance of the capacitor when using an infrared light-emitting diode in a gas sensor module can be made extremely small compared to the capacitance of the capacitor when using a tungsten lamp or MEMS heater in a gas sensor module.

[0044] When using infrared light-emitting diodes in a gas sensor module, a multilayer ceramic capacitor is one example of a suitable capacitor. Multilayer ceramic capacitors typically have a capacitance of the order of μF, are small in size, low in cost, and exhibit virtually no leakage current. On the other hand, when using tungsten lamps or MEMS heaters in a gas sensor module, an electric double-layer capacitor is one example of a suitable capacitor. Electric double-layer capacitors typically have a capacitance of the order of mF, are large in size, high in cost, and exhibit leakage currents on the order of μA.

[0045] In other words, by incorporating a non-dispersive infrared absorption gas sensor, which combines an infrared light-emitting diode and a quantum infrared sensor, the operating time per cycle of the infrared light-emitting diode 10 can be made extremely short, thus allowing the capacitance of the capacitor 40 to be made extremely small. This makes it possible to miniaturize and reduce the cost of not only the capacitor 40 but the entire gas sensor module 100.

[0046] The charging circuit 50 is provided between the power supply 60 and the capacitor 40. The charging circuit 50 is connected to the power supply 60 and also to the capacitor 40 via switch SW1. The charging circuit 50 receives the drive current I of the infrared light-emitting diode 10 from the power supply 60. drive The charging current I of capacitor 40 is smaller than that of capacitor 40. charge The charging circuit 50 then supplies the capacitor 40 with the charging current I to charge the capacitor 40. charge It supplies the charging current I of capacitor 40. charge The current is preferably around 1 mA. For example, if the detection period of the non-dispersive infrared absorption gas sensor is 10 s, the charging circuit 50 periodically supplies a current of 1.01 mA to the capacitor 40 for 9.9 s, while the driving circuit 30 instantaneously supplies a current of 100 mA to the infrared light-emitting diode 10 1000 times for 0.1 ms.

[0047] The charging circuit 50 is not particularly limited as long as it is a charging means whose current supply capacity is sufficiently low compared to the drive circuit 30, for example, about 1 / 100th. Examples of the charging circuit 50 include a resistor, a current source, a DC-DC converter, and a charge pump.

[0048] The charging circuit 50 and the capacitor 40 drive the infrared light-emitting diode 10 with a current I drive By having a function to average the emissions, it is possible to maintain the amount of light emitted by the infrared light-emitting diode 10 at roughly the same level as the amount of light emitted by the light-emitting unit 10A, while significantly reducing the load on the power supply 60.

[0049] <Timing Chart> Next, with reference to Figures 5A to 5C, Figure 6, and Figure 7, the differences between the gas sensor module 100 according to this embodiment and the conventional gas sensor module 100A will be explained. The following explanation will use the case where the detection period of the non-dispersive infrared absorption type gas sensor is 10s as an example.

[0050] [Gas sensor module 100 according to this embodiment] Referring to Figure 5A, the state of the infrared light-emitting diode 10 in the gas sensor module 100 according to this embodiment, and the drive current I of the infrared light-emitting diode 10. drive , the capacitor voltage V of capacitor 40 c , the charging current I of capacitor 40 charge Next, we will explain the state of the drive circuit 30 and the state of the amplification circuit / signal processing circuit 70.

[0051] The infrared light-emitting diode 10 repeatedly maintains a non-emitting state, switches from a non-emitting state to an emitting state, maintains the emitting state, and switches from an emitting state to a non-emitting state. The number of times the infrared light-emitting diode 10 emits light is 1000 times in a detection cycle of 10s. The operating time of the infrared light-emitting diode 10 per cycle is 100 μs. The non-operating time of the infrared light-emitting diode 10 per cycle is 9900 μs.

[0052] Driving current I of infrared light-emitting diode 10drive The system repeatedly maintains 0mA, switches from 0mA to 100mA, maintains 100mA, and switches from 100mA to 0mA. The drive current I of the infrared light-emitting diode 10 drive If the current remains at 0mA, the infrared light-emitting diode 10 will remain in a non-emitting state. The drive current I of the infrared light-emitting diode 10 drive When the current switches from 0mA to 100mA, the state of the infrared light-emitting diode 10 switches from a non-emitting state to an emitting state. The drive current I of the infrared light-emitting diode 10 drive If the current is maintained at 100mA, the infrared light-emitting diode 10 will maintain the light-emitting state. drive When the current switches from 100mA to 0mA, the state of the infrared light-emitting diode 10 switches from the emitting state to the non-emitting state.

[0053] The drive circuit 30 repeatedly maintains the off state, switches from the off state to the on state, maintains the on state, and switches from the on state to the off state. The number of on / off cycles of the drive circuit 30 is 1000 times in a detection cycle of 10s. The on time per cycle of the drive circuit 30 is 100μs. The off time per cycle of the drive circuit 30 is 9900μs. The duty cycle is expressed as [on time per cycle of the drive circuit 30 × number of on / off cycles of the drive circuit 30] / [detection cycle of the non-dispersive infrared absorbing gas sensor], so for example, Duty cycle = (100μs × 1000) / 10s = 1%. When the drive circuit 30 maintains the off state, the state of the infrared light-emitting diode 10 remains non-emitting. When the drive circuit 30 switches from the off state to the on state, the state of the infrared light-emitting diode 10 switches from non-emitting to emitting. When the drive circuit 30 remains in the ON state, the infrared light-emitting diode 10 remains in the emitting state. When the drive circuit 30 switches from the ON state to the OFF state, the infrared light-emitting diode 10 switches from the emitting state to the non-emitting state.

[0054] Capacitor voltage V of capacitor 40 cThe voltage repeatedly rises and falls. When switch SW1 is turned on (see Figures 5B and 5C), the charging current I of capacitor 40 is present between the power supply 60 and capacitor 40. charge As the current flows, capacitor 40 is charged, and the capacitor voltage V of capacitor 40 increases. c The voltage rises. In this case, the infrared light-emitting diode 10 remains in a non-emitting state. When switch SW2 is turned on (see Figures 5B and 5C), the drive current I of the infrared light-emitting diode 10 is present between capacitor 40 and drive circuit 30. drive As the current flows, capacitor 40 discharges, and the capacitor voltage V of capacitor 40 increases. c The value decreases. In this case, the state of the infrared light-emitting diode 10 remains in the light-emitting state.

[0055] Charging current I of capacitor 40 charge This is equal to the current of power supply 60. The charging current of capacitor 40 is I. charge The driving current I of the infrared light-emitting diode 10 drive The current is smaller than [the driving current I of the infrared light-emitting diode 10], and the required current is [I drive Since it is expressed as [on time / off time], for example, the charging current I of capacitor 40 charge =(100mA × (100μs × 1000) / (9900μA × 1000)) = 1.01mA. That is, the charging current I of capacitor 40. charge The driving current I of the infrared light-emitting diode 10 drive This is 1 / 99 times that. As is clear from Figure 5A, the drive current I of the infrared light-emitting diode 10 drive This is the current that instantaneously flows between the capacitor 40 and the infrared light-emitting diode 10 for 0.1 ms over a detection period of 10 s, at a rate of 100 mA 1000 times, but the charging current of the capacitor 40 is I charge This is the current that flows periodically between the power supply 60 and the capacitor 40 at a rate of 1.01mA for 9.9s during a detection cycle of 10s. In other words, the charging circuit 50 and the capacitor 40 drive the infrared light-emitting diode 10. driveBy having a function to average the values, it becomes possible to maintain the light output of the infrared light-emitting diode 10 at roughly the same level as the light output of the light-emitting unit 10A, while significantly reducing the load on the power supply 60. Charging current I charge The current only needs to be large enough to complete the charging of capacitor 40 within the given time, and therefore should be greater than 1.01mA. For example, 2mA would also be acceptable.

[0056] The amplification circuit / signal processing circuit 70 repeatedly maintains the off state, switches from the off state to the on state, maintains the on state, and switches from the on state to the off state. The number of on / off cycles of the amplification circuit / signal processing circuit 70 is 1000 times in a detection cycle of 10s. The on time for each cycle of the amplification circuit / signal processing circuit 70 is 100μs. The off time for each cycle of the amplification circuit / signal processing circuit 70 is 9900μs. In the amplification circuit / signal processing circuit 70, a detection signal is output from the quantum infrared sensor 20 to the amplification circuit / signal processing circuit 70 when it switches from the on state to the off state for the 1000th time.

[0057] Next, referring to Figures 5B and 5C, the capacitor voltage V of capacitor 40 c and the capacitor voltage V of capacitor 40 c This explains the details.

[0058] When switch SW2 is turned ON, the capacitor 40 and the drive circuit 30 are connected, and the drive current I of the infrared light-emitting diode 10 is supplied between the capacitor 40 and the infrared light-emitting diode 10. drive The current flows. In this case, the capacitor voltage V of capacitor 40 c The current decreases, and the capacitor 40 supplies the drive circuit 30 with the drive current I of the infrared light-emitting diode 10. drive By supplying this, capacitor 40 discharges.

[0059] When switching from switch SW2 to switch SW1, the voltage drop ΔV of the capacitor voltage Vc due to the discharge of capacitor 40 is equal to the voltage V of power supply 60. dd and the capacitor voltage V of capacitor 40 cThe minimum value V cmin This is the difference between the two, and is expressed by the following equation. Considering the power reduction of the gas sensor module 100, the voltage drop ΔV of the capacitor voltage Vc due to the discharge of the capacitor 40 is preferably around several hundred mV.

[0060]

number

[0061] When switch SW1 is turned ON, the charging circuit 50 and capacitor 40 are connected, and the charging current I of capacitor 40 is transmitted between the power supply 60 and capacitor 40. charge The current flows. In this case, the capacitor voltage V of capacitor 40 c The current increases, and the charging current I of capacitor 40 increases. charge When this is supplied, the capacitor 40 is charged.

[0062] Here, the capacitor voltage V of capacitor 40 c It is required that the following equation be satisfied.

[0063]

number

[0064] Furthermore, the voltage drop ΔV across the capacitor voltage Vc must satisfy the following equation.

[0065]

number

[0066] Therefore, the capacitance C of capacitor 40 bulk The voltage drop ΔV across the capacitor voltage Vc is equal to the voltage V of the power supply 60. dd From there, the drive voltage V of the infrared light-emitting diode 10emitter And the voltage V required for the drive circuit 30 to operate normally ds It is selected such that the value is smaller than the sum of the two values ​​minus the difference. Capacitor 40's capacitance C bulk It can be expressed by the following formula.

[0067]

number

[0068] From equation (4), the capacitance C of capacitor 40 is obtained. bulk This is the operating time t per cycle of the infrared light-emitting diode 10. ON It can be seen that this is a function that is approximately proportional to the value. In other words, the shorter the operating time of the infrared light-emitting diode 10 per cycle, the smaller the capacitance C of the capacitor 40. bulk It can be seen that it can be made smaller.

[0069] In other words, the gas sensor module 100 is equipped with a non-dispersive infrared absorption gas sensor that combines an infrared light-emitting diode and a quantum infrared sensor, thus reducing the operating time t per cycle of the infrared light-emitting diode 10. ON Because the distance can be made extremely short, the capacitance C of capacitor 40 bulk It can be seen that it can be made extremely small.

[0070] [Conventional gas sensor module 100A] Referring to Figures 6 and 7, the state of the light-emitting section 10A in the conventional gas sensor module 100A and the drive current I of the light-emitting section 10A. drive Next, we will explain the state of the drive circuit 30A and the state of the amplification circuit / signal processing circuit 70A.

[0071] The light-emitting unit 10A repeats maintaining a non-light-emitting state, switching from the non-light-emitting state to the light-emitting state, maintaining the light-emitting state, and switching from the light-emitting state to the non-light-emitting state. The number of light emissions of the light-emitting unit 10A is once in a detection period of 10 s. The driving time per emission of the light-emitting unit 10A is 0.1 s. The non-driving time per emission of the light-emitting unit 10A is 9.9 s.

[0072] The driving current I of the light-emitting unit 10A drive is equal to the current of the power supply 60A. The driving current I of the light-emitting unit 10A drive repeats maintaining 0 mA, switching from 0 mA to 100 mA, maintaining 100 mA, and switching from 100 mA to 0 mA. The driving current I of the light-emitting unit 10A drive When the driving current I of the light-emitting unit 10A maintains 0 mA, the state of the light-emitting unit 10A maintains the non-light-emitting state. The driving current I of the light-emitting unit 10A drive When the driving current I of the light-emitting unit 10A switches from 0 mA to 100 mA, the state of the light-emitting unit 10A switches from the non-light-emitting state to the light-emitting state. The driving current I of the light-emitting unit 10A drive When the driving current I of the light-emitting unit 10A maintains 100 mA, the state of the light-emitting unit 10A maintains the light-emitting state. The driving current I of the light-emitting unit 10A drive When the driving current I of the light-emitting unit 10A switches from 100 mA to 0 mA, the state of the light-emitting unit 10A switches from the light-emitting state to the non-light-emitting state.

[0073] The drive circuit 30A repeatedly maintains the off state, switches from the off state to the on state, maintains the on state, and switches from the on state to the off state. The number of on / off cycles of the drive circuit 30A is 1 in a detection cycle of 10s. The on time for each cycle of the drive circuit 30A is 0.1s. The off time for each cycle of the drive circuit 30A is 9.9s. The duty cycle is expressed as [on time per cycle of the drive circuit 30A × number of on / off cycles of the drive circuit 30A] / [detection cycle of the non-dispersive infrared absorbing gas sensor], so for example, Duty cycle = (0.1s × 1) / 10s = 1%. When the drive circuit 30A maintains the off state, the state of the light-emitting unit 10A remains non-emitting. When the drive circuit 30A switches from the off state to the on state, the state of the light-emitting unit 10A switches from non-emitting to emitting. When the drive circuit 30A remains in the ON state, the state of the light-emitting unit 10A remains in the illuminated state. When the drive circuit 30A switches from the ON state to the OFF state, the state of the light-emitting unit 10A switches from the illuminated state to the non-illuminated state.

[0074] The amplification circuit / signal processing circuit 70A repeatedly maintains the off state, switches from the off state to the on state, maintains the on state, and switches from the on state to the off state. The number of on / off cycles of the amplification circuit / signal processing circuit 70A is 1 in a detection cycle of 10s. The on time for each cycle of the amplification circuit / signal processing circuit 70A is 0.1s. The off time for each cycle of the amplification circuit / signal processing circuit 70A is 9.9s. In the amplification circuit / signal processing circuit 70A, a detection signal is output from the light receiving unit 20A, such as a pyroelectric sensor or thermopile, to the amplification circuit / signal processing circuit 70A when it switches from the on state to the off state for the first time.

[0075] [Comparison] As described above, the operating time per cycle of the infrared light-emitting diode 10 is 1 / 1000th of the operating time per cycle of the light-emitting unit 10A. In other words, the gas sensor module 100 according to this embodiment can achieve an extremely short operating time per cycle of the infrared light-emitting diode compared to the conventional gas sensor module 100A.

[0076] Furthermore, it can be seen that the peak current of power supply 60 is 1 / 100th of the peak current of power supply 60A. In other words, it can be seen that the gas sensor module 100 according to this embodiment can significantly reduce the load on the power supply compared to the conventional gas sensor module 100A.

[0077] Furthermore, it can be seen that the on-time of the drive circuit 30 per cycle is 1 / 1000th of the on-time of the drive circuit 30A per cycle. In other words, compared to the conventional gas sensor module 100A, even with the same duty cycle, the gas sensor module 100 according to this embodiment can make the on-time of the drive circuit 30 per cycle of the infrared light-emitting diode 10 shorter than the on-time of the drive circuit 30A per cycle of the light-emitting unit 10A, thus significantly reducing the load on the power supply.

[0078] The gas sensor module 100 according to this embodiment utilizes the periodic emission of an infrared light-emitting diode 10 included in a non-dispersive infrared absorbing gas sensor to drive the infrared light-emitting diode 10. drive With a current smaller than that, the charging circuit 50 charges the capacitor 40, and the capacitor 40 supplies the drive circuit 30 with the drive current I of the infrared light-emitting diode 10. drive This provides a supply of power. As a result, compared to the conventional gas sensor module 100A, the load on the power supply 60 can be significantly reduced without changing the amount of light emitted by the infrared light-emitting diode 10. Furthermore, it can stabilize its own operation without adversely affecting the operation of other devices mounted on the same board (for example, other environmental sensors).

[0079] Furthermore, the gas sensor module 100 according to this embodiment includes a non-dispersive infrared absorption type gas sensor that combines an infrared light-emitting diode and a quantum infrared sensor. Compared to the case where a tungsten lamp or MEMS heater is combined with a thermopile or pyroelectric sensor, the operating time per cycle of the infrared light-emitting diode 10 can be made extremely short. As a result, the capacity of the capacitor 40 can be made extremely small, which enables miniaturization and cost reduction of the entire gas sensor module 100.

[0080] <Variation> The present invention is not limited to the embodiments and modifications described above. For example, the various processes described above may not only be performed sequentially as described, but may also be performed in parallel or individually as needed, depending on the processing capacity of the device performing the processes. Other modifications can be made as appropriate without departing from the spirit of the present invention.

[0081] Although the embodiments described above are representative examples, it will be apparent to those skilled in the art that many modifications and substitutions are possible within the spirit and scope of this disclosure. Therefore, the present invention should not be interpreted as being limited by the embodiments described above, and various modifications and changes are possible without departing from the claims. For example, it is possible to combine multiple component blocks shown in the configuration diagram of the embodiments into one, or to divide one component block. [Explanation of symbols]

[0082] 10. Infrared light-emitting diode 20 Quantum-type infrared sensors 30 Drive Circuit 40 Capacitors 50 Charging circuit 60 power supply 70 Amplifier Circuits / Signal Processing Circuits 100 Gas Sensor Modules 10A Light-emitting part 20A Light receiving section 30A drive circuit 60A power supply 70A Amplifier Circuit / Signal Processing Circuit 100A Conventional gas sensor module

Claims

1. An infrared light-emitting diode that emits infrared light according to the drive current, A quantum infrared sensor that receives infrared light transmitted through the target gas, A drive circuit that outputs the aforementioned drive current to the infrared light-emitting diode, A charging circuit connected to a power supply and outputting a charging current smaller than the drive current, A capacitor that is charged by the supply of the charging current from the charging circuit and discharged by the supply of the drive current to the drive circuit, A first switch connected between the charging circuit and the capacitor, Equipped with, The first switch is in an ON state while the capacitor is being charged and in an OFF state while the infrared light-emitting diode is being driven in the gas sensor module.

2. Further comprising a second switch connected between the drive circuit and the capacitor, The second switch is in the ON state while the infrared light-emitting diode is being driven, and in the OFF state while the capacitor is being charged. The gas sensor module according to claim 1.

3. When the first switch is in the ON state, the second switch is in the OFF state. When the second switch is in the ON state, the first switch is in the OFF state. The gas sensor module according to claim 2.

4. The quantum infrared sensor has an optical filter, The gas sensor module according to claim 1.

5. The gas sensor module is a non-dispersive infrared absorption gas sensor module that detects the amount of infrared absorption by the target gas having infrared absorption characteristics according to the amount of infrared light received by the quantum infrared sensor, and calculates the concentration of the target gas. The gas sensor module according to claim 1.

6. The product of the charging current and charging time is greater than or equal to the product of the driving current and driving time. The gas sensor module according to claim 1.

7. The aforementioned driving time is 1 ms or less. The gas sensor module according to claim 6.

8. The on-duty cycle of the aforementioned drive current is 10% or less. The gas sensor module according to claim 1.

9. The capacitor is a multilayer ceramic capacitor. The gas sensor module according to claim 1.

10. The capacitor has a capacitance of 1 mF or less. The gas sensor module according to claim 1.

11. A nondispersive infrared absorption gas sensor includes an infrared light-emitting diode that emits infrared light in response to a drive current and a quantum infrared sensor that receives infrared light transmitted through a target gas, and a drive circuit that outputs the drive current to the infrared light-emitting diode, A charging circuit that outputs a charging current smaller in amount than the aforementioned drive current, A capacitor that is charged by the supply of the charging current from the charging circuit and discharged by the supply of the drive current to the drive circuit, A first switch connected between the charging circuit and the capacitor, Equipped with, The first switch is a circuit for a gas sensor module that is ON while the capacitor is being charged and OFF while the infrared light-emitting diode is being driven.

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