JP2009276310A - Fluid detecting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluid detecting apparatus capable of cost reduction, while inhibiting a longer measurement time and lower responsiveness. <P>SOLUTION: The fluid detecting apparatus 1 comprises a comparator 40, which controls a changeover switch 50, based on a comparison result of an analog signal Sc amplified by an amplifier 30 and a predetermined voltage. The changeover switch 50 is changed-over between a first setting and a second setting, and supplies a 0.5 V first reference voltage to an AD converter 60 at a first setting, and supplies a 4 V second reference voltage to the AD converter 60 at a second setting. The AD converter 60 has an overlapping area which equalizes a digital signal Sd to be output on the occasion of the first setting and a digital signal Sd to be output, at the second setting, when fluid information computed by a microcomputer 70 is different. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fluid detection device.

  Conventionally, a flow sensor manufactured by using a semiconductor manufacturing process technology is known. Such a flow sensor has a capability of detecting a flow rate and a flow rate of three digits or more (see, for example, Patent Documents 1 and 2). Here, the ability to detect a three-digit flow velocity or flow rate means that an error is allowed at the same ratio to the reading up to “999” for the minimum detection unit “1”. In other words, if an error of ± 3% is allowed, the detection capability is such that an error of up to ± 0.03 is allowed for “1” and an error of up to about ± 30 is allowed for “999”. Hereinafter, such a detection error is expressed as% RD (% of Reading).

  However, when detecting a flow rate and flow rate of three digits or more, the AD value of an analog-digital converter that converts an analog signal from a flow sensor into a digital signal becomes high. Specifically, the AD value is as shown in Equation 1.

AD = F / (m × 2/100) (1)
Here, assuming that a flow rate of 999 m / sec or a flow rate of up to 999 l / sec is detected, the value of F is “999”. Further, when the accuracy of the analog-digital converter is ± 3% RD, m is “3”. For this reason, AD = 999 / (3 × 2/100), and the AD value needs to be “16650”. Therefore, the analog-digital converter needs 15-bit capability. In particular, considering the disturbance error factor, the accuracy of the analog-to-digital converter needs to be about ± 1% RD, AD = 999 / (1 × 2/100), the AD value is “49950”, and the analog-digital converter The converter needs 16-bit capability. And such an analog-digital converter is not cheap at all.

  Moreover, not only when detecting a flow rate and flow rate of 3 digits or more, but also when detecting a flow rate and flow rate of 2 digits, according to the above equation (1), the analog-digital converter has a 13-bit capability. Needed and not cheap at all.

  Therefore, the present applicant has found that the number of bits of the analog-digital converter can be reduced by using a technique as described in Patent Documents 3 to 5 (see Patent Documents 3 to 5).

  The fluid detection device described in Patent Document 3 includes a flow sensor, an analog / digital converter that performs analog / digital conversion on an analog flow detection signal output from the flow sensor, and a digital flow detection signal that is digitized by the analog / digital converter. And a microcomputer for measuring the flow rate. In this fluid detection device, when the flow rate obtained by the microcomputer is equal to or higher than a predetermined flow rate, the reference voltage supplied to the analog-digital converter is changed.

  By changing the reference voltage, the applicant has found that the number of bits of the analog-digital converter can be reduced. In other words, if the reference voltage is changed, it is possible to output digital signals with the same value for different flow rates before and after the change, reducing the AD value and reducing the number of bits of the analog-digital converter. Can do. More specifically, first, the flow sensor outputs an analog signal (an analog voltage or current signal) having a value b1 with respect to the flow velocity a1. The analog-digital converter inputs an analog signal having a value b1 and outputs a digital signal having a value d. On the other hand, when the reference voltage is changed, the resolution of the analog-digital converter is changed. For this reason, the flow sensor outputs an analog signal of value b2 for a flow velocity a2 different from the flow velocity a1, and the analog-digital converter inputs the analog signal of value b2 and outputs a digital signal Sd of value d. Is possible. In this manner, the digital signal Sd having the same value d is output for the different flow rates a1 and a2. For this reason, the digital signal of the value d corresponds to the flow rates a1 and a2, and the AD value can be reduced as compared with the case where digital signals of different values are output corresponding to the flow rates a1 and a2. It can be linked to reducing the number.

  Further, the fluid detection device described in Patent Document 4 includes a bridge circuit including a temperature sensor and a fixed resistor, a differential amplifier, and a CPU. In this device, when the ambient temperature of the temperature sensor changes, the resistance value of the temperature sensor changes, and the balance of the bridge circuit is lost. The voltage obtained by the breakdown is amplified in the differential amplifier and taken into the CPU. Calculate the flow rate. Further, since it is difficult to adjust the balance of the bridge circuit, this device includes means for offsetting so that the output voltage from the bridge circuit becomes zero when the flow rate is zero. In such an apparatus, when a voltage outside the flow rate measurement range is obtained by a microcomputer or the like, the voltage value of the offset added voltage is changed.

  By this change in the addition voltage, the present applicant has found that the number of bits of the analog-digital converter can be reduced. In other words, changing the added voltage makes it possible to output digital signals with the same value for different flow rates before and after the change, reducing the AD value and reducing the number of bits of the analog-digital converter. Can do. More specifically, first, the flow sensor outputs an analog signal having a value b1 with respect to the flow velocity a1. The differential amplifier amplifies the analog signal of value b1 and adds the added voltage to output an analog signal of value c. The analog-to-digital converter inputs an analog signal having a value c and outputs a digital signal having a value d. On the other hand, when the addition voltage is changed, the following occurs. First, the flow sensor outputs an analog signal having a value b2 with respect to the flow velocity a2. The differential amplifier amplifies the analog signal having the value b2 and adds the addition voltage. At this time, the value of the output analog signal can be set to the same value c as that of the analog signal according to the value of the addition voltage. For this reason, the analog-to-digital converter inputs an analog signal having a value c and outputs a digital signal having a value d. Thus, digital signals having the same value d are output for different flow velocities a1 and a2. For this reason, the digital signal of the value d corresponds to the flow rates a1 and a2, and the AD value can be reduced as compared with the case where digital signals of different values are output corresponding to the flow rates a1 and a2. It can be linked to reducing the number.

  Further, the fluid detection device described in Patent Document 5 includes a bridge circuit including a heater element and an operational amplifier. In this device, in order to make the temperature of the heater element variable, a plurality of resistors are arranged in parallel in one resistor portion of a bridge circuit composed of four resistors, and any one of the plurality of resistors is switched by a switch device. You can choose one. According to this fluid detection device, the resistance is selected according to the flow rate calculated by a microcomputer or the like.

  By selecting this resistor, the present applicant has found that the number of bits of the analog-digital converter can be reduced. In other words, if the resistance is selected and changed, the same digital signal can be output for different flow rates before and after the change, the AD value can be reduced, and the number of bits of the analog-digital converter can be reduced. Can be connected. More specifically, first, the temperature of the heater element becomes a predetermined temperature by setting the resistance. The flow sensor outputs an analog signal having a value b with respect to the flow velocity a1. The analog-to-digital converter inputs an analog signal having a value b and outputs a digital signal having a value d. On the other hand, when the resistance is changed, the heater element has a temperature different from the predetermined temperature. The analog signal output from the flow sensor is affected by the flow velocity and the heater temperature. For this reason, the flow sensor may output an analog signal having a value b with respect to the flow velocity a2. In this case, the analog-digital converter inputs an analog signal having a value b and outputs a digital signal having a value d. Thus, digital signals having the same value d are output for different flow velocities a1 and a2. For this reason, the digital signal of the value d corresponds to the flow rates a1 and a2, and the AD value can be reduced as compared with the case where digital signals of different values are output corresponding to the flow rates a1 and a2. It can be linked to reducing the number.

The present applicant has found that the AD value can be reduced and the number of bits can be reduced by techniques other than those described above.
Japanese Patent No. 3381831 Japanese Patent No. 4050857 Japanese Patent No. 3585099 (see claim 1 and FIG. 1) Japanese Patent No. 3738897 (see paragraph [0010]) Japanese Patent Publication No. 7-3353 (see FIG. 3)

  However, in the fluid detection devices described in Patent Documents 3 to 5, the flow velocity and flow rate of the fluid are determined by a microcomputer or the like, and according to this, the reference voltage is changed, the offset addition voltage is changed, and the resistance is changed. Is going. For this reason, the microcomputer must change the reference voltage, etc. once it calculates the flow velocity, etc., and must perform the flow rate calculation again from the digital signal obtained after the change, resulting in a longer measurement time and responsiveness. Will fall.

  The present invention has been made to solve such a conventional problem, and the object of the present invention is to reduce the cost while suppressing an increase in measurement time and a decrease in responsiveness. The object is to provide a fluid detection device.

  The fluid detection device of the present invention includes a flow sensor that outputs an analog signal corresponding to a fluid flow velocity, an analog-to-digital converter that inputs an analog signal from the flow sensor, converts the analog signal to output, and a flow sensor. The analog signal and the predetermined voltage are input, and a comparator that outputs the first signal or the second signal according to the comparison result, and the first setting when the first signal from the comparator is output, are set to the first setting. The second switch when the second signal is output, the first signal or the second signal output from the comparator, and the digital signal output from the analog-to-digital converter, A microcomputer that calculates fluid information including at least one of a flow rate and a flow rate, and the analog-digital converter includes: When i black fluid information calculated by the computer is different, and having a digital signal to be output to the first setting time, an overlapping area a value the same with the digital signal to be outputted to the second setting.

  Further, in the fluid detection device of the present invention, the changeover switch uses the reference voltage, which is a reference when the analog-digital converter converts the analog signal to the digital signal, as the first reference voltage at the first setting, and the second setting. It is preferable that the second reference voltage is different from the first reference voltage.

  In the fluid detection device of the present invention, the change-over switch has a first lower limit voltage in which the upper limit value of the reference voltage is set to the first upper limit voltage and the lower limit value of the reference voltage is smaller than the first upper limit voltage at the first setting. In the second setting, it is preferable that the upper limit value of the reference voltage is the second upper limit voltage and the lower limit value of the reference voltage is a second lower limit voltage smaller than the second upper limit value.

  The fluid detection device of the present invention further includes an amplifier that amplifies the analog signal from the flow sensor and adds a predetermined voltage to supply the analog signal to the analog-to-digital converter, and the changeover switch adds the amplifier. The addition voltage is preferably the first addition voltage at the time of the first setting and the second addition voltage different from the first addition voltage at the time of the second setting.

  The fluid detection device of the present invention further includes an amplifier that amplifies an analog signal from the flow sensor and supplies the analog signal to the analog-digital converter, and the changeover switch sets the amplification factor of the amplifier at the first setting to the first amplification factor. In the second setting, the amplification factor of the amplifier is preferably a second amplification factor different from the first amplification factor.

  Further, in the fluid detection device of the present invention, the changeover switch sets the driving power supplied to the heater of the flow sensor to the first power value at the first setting, and the second power different from the first power value at the second setting. It is preferable to set the power value.

  In the fluid detection device of the present invention, the flow sensor corrects the flow rate or flow rate of the fluid calculated based on the first sensor that outputs an analog signal corresponding to the fluid flow rate and the analog signal from the first sensor. A second sensor that outputs an analog signal for correction, and an analog-to-digital converter receives the analog signal from the first sensor among the flow sensors, converts the analog signal to a digital signal, and outputs the first analog-digital signal A converter and a second analog-to-digital converter that inputs the analog signal for correction from the second sensor, converts the signal into a digital signal for correction, and outputs the digital signal. The comparator is supplied from the first sensor or the second sensor. The first signal or the second signal is output according to the comparison result between the first signal and the predetermined voltage, and the changeover switch is activated when the first signal from the comparator is output. 1 setting, when the second signal from the comparator is output, the first changeover switch becomes the second setting, and when the first signal from the comparator is output, the third setting is set, and the second signal from the comparator And a second changeover switch that is set to a fourth setting when the first and second analog switches are output, and the first analog-digital converter outputs the first setting when the fluid information calculated by the microcomputer is different The second analog-to-digital converter has an overlapping region where the values of the digital signal and the digital signal output at the time of the second setting are the same, and the second analog-to-digital converter has a third value when the correction information calculated by the microcomputer is different. An overlapping area in which the values of the correction digital signal output at the time of setting and the correction digital signal output at the time of the fourth setting are the same The microcomputer calculates the fluid information based on the first signal or the second signal output from the comparator and the digital signal output from the first analog-digital converter, and outputs the fluid information from the comparator. It is preferable to correct the calculated fluid information based on the one signal or the second signal and the correction digital signal output from the second analog-digital converter.

  According to the fluid detection device of the present invention, when the fluid information calculated by the microcomputer is different, the analog-digital converter includes a digital signal output at the first setting and a digital signal output at the second setting. Have overlapping areas with the same value. For this reason, one value of digital signal can be assigned to different flow velocities. That is, the analog-digital converter outputs a digital signal Sd having a value d with respect to the analog signal Sb obtained by the flow rate a1, and for the analog signal Sb obtained by the flow rate a2 different from the flow rate a1. A digital signal Sd having the same value d can be output. As a result, one value d is assigned to the digital signal Sd for the different flow rates a1 and a2, and the digital signal Sd having the value d1 is output for the flow rate a1 and the value for the flow rate a2. Compared with the case of outputting the digital signal Sd of d2, the value of the digital signal Sd can be made one. Thus, when the same digital signal Sd is obtained at different flow rates a1 and a2, the range of fluid information obtained by the first setting and the range of fluid information obtained by the second setting can be set differently. A wider range of fluid information can be measured than in a single setting, and the AD value of the analog-to-digital converter can be reduced accordingly, leading to a reduction in the number of bits. In addition, since the switching between the first setting and the second setting is performed by the output from the comparator, the microcomputer does not need to perform the switching after calculating the flow velocity, the flow rate, and the like. Therefore, it is possible to reduce costs while suppressing an increase in measurement time and a decrease in responsiveness.

  Further, the reference voltage is the first reference voltage at the time of the first setting, and the reference voltage is the second reference voltage at the time of the second setting. As described above, when the reference voltage is changed, the resolution of the analog-digital converter is changed. Thereby, for example, at the time of the first setting, the flow sensor outputs the analog signal Sb having the value b1 with respect to the flow velocity a1, and the analog-digital converter inputs the amplified analog signal Sc having the value c1. A digital signal Sd having a value d is output. On the other hand, at the time of the second setting, the flow sensor outputs an analog signal Sb having a value b2 for a flow velocity a2 different from the flow velocity a1, and the analog-digital converter inputs the amplified analog signal Sc having a value c2. It becomes possible to output a digital signal Sd having a value d. In this manner, the digital signal Sd having the same value d is output for the different flow rates a1 and a2. For this reason, the digital signal Sd corresponds to the flow velocities a1 and a2. In this way, by changing the reference voltage, it is possible to create an overlapping region where the output digital signal Sd has the same value when the fluid information calculated by the microcomputer is different. Therefore, it is possible to reduce the cost while suppressing a decrease in responsiveness.

  In the first setting, the upper limit value of the reference voltage is the first upper limit voltage, the lower limit value of the reference voltage is the first lower limit voltage, and in the second setting, the upper limit value of the reference voltage is the second upper limit voltage. In addition, the lower limit value of the reference voltage is set as the second lower limit voltage. For this reason, even in the analog-to-digital converter that can set the upper limit value and the lower limit value of the reference voltage, the cost can be reduced while suppressing a decrease in responsiveness.

  In addition, an addition voltage added by the amplifier at the first setting is a first addition voltage, and an addition voltage added by the amplifier at the second setting is a second addition voltage. Thereby, for example, at the time of the first setting, the flow sensor outputs an analog signal Sb having a value b1 with respect to the flow velocity a1. The amplifier amplifies the analog signal Sb having the value b1 and outputs the analog signal Sc having the value c obtained by adding and adding the first addition voltage. The analog-digital converter inputs an analog signal Sc having a value c and outputs a digital signal Sd having a value d. On the other hand, at the time of the second setting, the flow sensor outputs an analog signal Sb having a value b2 with respect to the flow velocity a2. The amplifier amplifies the analog signal Sb having the value b2 and adds the second addition voltage. At this time, depending on the value of the added voltage, the value of the analog signal Sc amplified and added can be made the same as the analog signal Sc having the value c. For this reason, the analog-digital converter inputs the analog signal Sc having the value c after amplification and addition, and outputs the digital signal Sd having the value d. In this manner, the digital signal Sd having the same value d is output for the different flow rates a1 and a2. For this reason, the digital signal Sd having the value d corresponds to the flow velocities a1 and a2. In this way, by changing the addition voltage, it is possible to create an overlapping region where the output digital signal Sd has the same value when the fluid information calculated by the microcomputer is different. Therefore, it is possible to reduce the cost while suppressing a decrease in responsiveness.

  Further, the amplification factor of the amplifier is set to the first amplification factor at the first setting, and the amplification factor of the amplifier is set to the second amplification factor at the second setting. Thereby, for example, at the time of the first setting, the flow sensor outputs an analog signal Sb having a value b1 with respect to the flow velocity a1. The amplifier amplifies the analog signal Sb having the value b1 and outputs the analog signal Sc having the value c. The analog-digital converter inputs an analog signal Sc having a value c and outputs a digital signal Sd having a value d. On the other hand, at the time of the second setting, the flow sensor outputs an analog signal Sb having a value b2 with respect to the flow velocity a2. The amplifier amplifies the analog signal Sb having the value b2. At this time, the value of the analog signal Sc to be output can be made the same as the analog signal Sc having the value c depending on the value of the amplification factor. For this reason, the analog-digital converter inputs the analog signal Sc having the value c and outputs the digital signal Sd having the value d. Thus, the digital signal Sd having the same value is output for the different flow rates a1 and a2. For this reason, the digital signal Sd corresponds to the flow velocities a1 and a2. As described above, when the fluid information calculated by the microcomputer is different, it is possible to create an overlapping region where the values of the output digital signals are the same. Therefore, it is possible to reduce the cost while suppressing a decrease in responsiveness.

  Further, the driving power supplied to the heater of the flow sensor is set to the first power value at the first setting, and the second power value different from the first power value at the second setting. Thereby, for example, at the time of the first setting, the flow sensor outputs an analog signal Sb having a value b with respect to the flow velocity a1. The analog-to-digital converter inputs an analog signal Sb having a value b and outputs a digital signal Sd having a value d. On the other hand, the heater temperature is different in the second setting. For this reason, the flow sensor can output the analog signal Sb having the same value b as the analog signal Sb with respect to the flow velocity a2. The analog-to-digital converter inputs an analog signal Sb having a value b and outputs a digital signal Sd having a value d. In this manner, the digital signal Sd having the same value d is output for the different flow rates a1 and a2. For this reason, the digital signal Sd having the value d corresponds to the flow velocities a1 and a2. As described above, when the fluid information calculated by the microcomputer is different, it is possible to create an overlapping region where the values of the output digital signals are the same. Therefore, it is possible to reduce the cost while suppressing a decrease in responsiveness.

  The changeover switch has a first changeover switch and a second changeover switch, and the first analog-digital converter and the second analog-digital converter have overlapping areas. For this reason, it is not necessary to switch the amplification factor, the heater temperature, or the like by a single changeover switch as compared with the case where the amplification factor, the heater temperature, or the like is switched. Therefore, it is possible to suppress a decrease in measurement accuracy due to a large switching by one switching switch.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing a fluid detection device according to the first embodiment of the present invention. As shown in FIG. 1, the fluid detection device 1 calculates fluid information including at least one of a flow velocity and a flow rate based on the sensor output. The fluid detection device 1 includes a flow sensor 10, a heater drive circuit 20, an amplifier 30, a comparator 40, a changeover switch 50, an AD converter (analog / digital converter) 60, a microcomputer 70, and resistors R1 to R1. R3.

  The flow sensor 10 outputs an analog signal Sb corresponding to the flow velocity of the fluid. The flow sensor 10 includes a heater 11 and a temperature sensor 12. The heater 11 warms the fluid by heat generation. The temperature sensor 12 outputs an analog signal Sb corresponding to the fluid temperature warmed by the heater 11. The flow sensor 10 is configured to output an analog signal Sb corresponding to the flow velocity based on the change in the fluid temperature detected by the temperature sensor 12 according to the fluid flow velocity.

  The heater drive circuit 20 controls the heater temperature of the flow sensor 10. The heater drive circuit 20 is configured to control the temperature of the heater 11 so as to be a temperature that is higher than the ambient temperature by a certain temperature, for example.

  The amplifier 30 amplifies the analog signal Sb from the flow sensor 10 with a predetermined amplification factor. The analog signal Sc amplified by the amplifier 30 is input to the inverting input terminal of the comparator 40 and the AD converter 60.

  The comparator 40 receives the analog signal Sc output from the flow sensor 10 and amplified by the amplifier 30 and a predetermined voltage Vref (for example, 0.385 V), and a signal of “0” or “1” depending on the comparison result. Is output. Specifically, the comparator 40 outputs a signal “0” in the low flow rate region and outputs a signal “1” in the high flow rate region. Hereinafter, the “0” signal output from the comparator 40 is referred to as a first signal, and the “1” signal is referred to as a second signal.

  As shown in FIG. 1, the comparator 40 is configured to have a hysteresis. That is, the predetermined voltage Vref is input to the non-inverting input terminal of the comparator 40 via the resistor R1 (for example, 600Ω), and the output voltage of the comparator 40 is input to the comparator 40 via the resistor R2 (for example, 49 kΩ). Is input to the non-inverting input terminal. A voltage Vmax (for example, 5 V) is applied to the output side of the comparator 40 via the resistor R3.

  FIG. 2 is a diagram showing an operation of the comparator shown in FIG. As shown in FIG. 2, when the voltage signal input to the inverting input terminal, that is, the amplified analog signal Sc reaches 0.44 V from a state below 0.44 V, for example, the comparator 40 outputs a signal of “1”. A certain second signal is output. Further, even if the amplified analog signal Sc becomes 0.44 V or lower from the state of 0.44 V or higher, the comparator 40 outputs the second signal until it reaches 0.38 V. When the amplified analog signal Sc reaches 0.38 V, the comparator 40 outputs a first signal that is a “0” signal. Further, from this state, even if the amplified analog signal Sc becomes 0.38V or higher, the comparator 40 outputs the first signal until it reaches 0.44V. In the following description, 0.38V is referred to as a lower limit threshold, and 0.44V is referred to as an upper limit threshold.

  Thus, the comparator 40 has hysteresis, prevents the output of the comparator 40 from being frequently switched, and prevents the occurrence of noise due to frequent switching. Further, immediately after switching, there is a period in which the output voltage of the comparator 40 is not stable, and the measurement accuracy in this period is prevented from being lowered. In particular, some comparators 40 have poor responsiveness at the time of switching, and providing hysteresis is more effective when the period during which the output voltage is not stable becomes longer due to such comparators 40.

  Reference is again made to FIG. As shown in FIG. 1, the first signal and the second signal from the comparator 40 are input to the changeover switch 50 and the microcomputer 70. The changeover switch 50 is set to the first setting when the first signal is output from the comparator 40 and is set to the second setting when the second signal is output. Further, the changeover switch 50 supplies the first reference voltage to the AD converter 60 at the time of the first setting, and supplies the second reference voltage different from the first reference voltage to the AD converter 60 at the time of the second setting. become. Here, the reference voltage is a voltage that becomes a reference when the AD converter 60 converts the analog signal Sc into the digital signal Sd. Specifically, the resolution of the AD converter 60 is determined according to the reference voltage and the number of bits of the AD converter 60. For example, when the reference voltage is 4V and the AD converter 60 is 11 bits, the resolution is 4000/2048 = about 1.95 mV. In the present embodiment, the first reference voltage is 0.5V, and the second reference voltage is 4V.

  The microcomputer 70 calculates fluid information including at least one of a flow rate and a flow rate. The microcomputer 70 receives the first signal or the second signal from the comparator 40 and the digital signal Sd from the AD converter 60, and calculates fluid information based on these signals.

  In particular, in the present embodiment, the AD converter 60 has an overlapping region. Here, when the fluid information calculated by the microcomputer 70 is different, the overlapping region is a digital signal Sd output from the AD converter 60 at the first setting and output from the AD converter 60 at the second setting. This is a region where the value of the digital signal Sd is the same.

  Hereinafter, the overlapping area will be specifically described. 3A and 3B are diagrams for explaining the overlapping region. FIG. 3A shows the relationship between the analog signal Sc and the digital signal Sd when the reference voltage is 0.5V, and FIG. 3B is the case when the reference voltage is 4V. The relationship between the analog signal Sc and the digital signal Sd is shown.

  First, when the flow rate is low and the first signal is output from the comparator 40, the changeover switch 50 is set to the first setting, and a voltage of 0.5 V that is the first reference voltage is supplied to the AD converter 60. If the AD converter 60 has 11 bits, as shown in FIG. 3A, the AD converter 60 converts the analog signal Sc into a digital signal Sd in increments of about 500/2048 = about 0.244 mV. It becomes. Further, since the upper limit threshold is 0.44V, the AD converter 60 converts the analog signal Sc into the digital signal Sd at intervals of about 0.244 mV between 0V and 0.44V.

  Therefore, when the analog signal Sc of 0.244 mV is input, the AD converter 60 outputs the digital signal Sd of “1”. Similarly, the AD converter 60 outputs a digital signal Sd of “2” when an analog signal Sc of 0.488 mV is input, and outputs a digital signal Sd of “3” when an analog signal Sc of 0.732 mV is input. To do. When the AD converter 60 receives the analog signal Sc of 439.8 mV (the same applies to 440.0 mV), the AD converter 60 outputs the digital signal Sd of “1802”.

  On the other hand, when the flow velocity becomes high and the second signal is output from the comparator 40, the changeover switch 50 is set to the second setting, and the voltage of 4V that is the second reference voltage is supplied to the AD converter 60. As a result, as shown in FIG. 3B, the AD converter 60 converts the analog signal Sc into the digital signal Sd in increments of 4000/2048 = about 1.95 mV. When the lower limit threshold is 0.38V and the AD converter 60 performs AD conversion up to an analog signal Sc of 3.8V at the maximum, the AD converter 60 is approximately 1.95 mV between 0.38V and 3.8V. The analog signal Sc is converted into a digital signal Sd in increments.

  Specifically, when the analog signal Sc of 380.85 mV is input, the AD converter 60 outputs the digital signal Sd of “195”. Similarly, when the analog signal Sc of 382.83 mV is input, the AD converter 60 outputs the digital signal Sd of “196”, and when the analog signal Sc of 384.77 mV is input, the AD converter 60 outputs the digital signal Sd of “197”. To do. When the AD converter 60 receives the analog signal Sc of 3798.82 mV (the same applies to 3800 mV), the AD converter 60 outputs the digital signal Sd of “1945”.

  As described above, the AD converter 60 is able to output digital signals having the same value within the range of “195” to “1802” even though the analog signal Sc is different, that is, the fluid flow velocity is different. The signal Sd is output. Such an area from “195” to “1802” is called an overlapping area in this embodiment.

  In addition, when providing the fluid detection apparatus 1 within 3% of error RD, it is good to do as follows. Specifically, when realizing an error of 3% RD, the AD converter 60 needs to have an error of about 1% RD in consideration of the influence of disturbance. Here, as shown in FIG. 3A, in order to realize an error of 1% RD in increments of 0.244 mV, it is necessary to exclude the digital signal Sd from less than “50”.

  This will be specifically described. First, it is assumed that an analog signal Sc of 0.244 mV is input to the AD converter 60. In this case, the microcomputer 70 calculates the flow velocity and the flow rate based on the digital signal Sd “1” output from the AD converter 60 and the first signal output from the comparator 40. Then, it is assumed that the microcomputer 70 calculates the flow rate R1. Similarly, it is assumed that an analog signal Sc of 0.365 mV (0.244 mV + 0.121 mV) is input to the AD converter 60. In this case, the microcomputer 70 calculates the flow velocity and the flow rate based on the digital signal Sd “1” output from the AD converter 60 and the first signal output from the comparator 40. Also at this time, the microcomputer 70 calculates the flow rate R1. However, when comparing the analog signal Sc, it is 0.244: 0.365≈1: 1.5, and the flow rate of the latter should be about 1.5 times that of the former. Therefore, the error is 50%, far exceeding the error 3% RD. Therefore, the fluid detection device 1 excludes a range in which a minute voltage is input from the measurement target in order to realize 3% RD (1% RD considering disturbance).

  Here, it verifies about 12.207mv. The AD converter 60 outputs a digital signal Sd of “50” when an analog signal Sc of 12.207 mV is input. Then, the microcomputer 70 calculates the flow rate R2. On the other hand, when an analog signal Sc of 12.328 mV (12.207 mV + 0.121 mV) is input, the AD converter 60 outputs a digital signal Sd of “50”. Then, the microcomputer 70 calculates the flow rate R2. Here, when comparing the analog signal Sc, it is 12.207: 12.3328≈1: 1.01, and the error is about 1%. Therefore, the fluid detection device 1 excludes the range where the value of the digital signal Sd is less than “50” from the measurement target.

  Next, operation | movement of the fluid detection apparatus 1 which concerns on this embodiment is demonstrated. First, when the power source of the fluid detection device 1 is turned on, the heater drive circuit 20 is driven to warm the heater 11. And the temperature sensor 12 outputs the analog signal Sb according to detected temperature. The amplifier 30 amplifies the analog signal Sb. As a result, the amplified analog signal Sc is input to the inverting input terminal of the comparator 40.

  Then, the first signal or the second signal is output according to the comparison result with the reference voltage Vref. Here, the comparator 40 outputs a first signal if the fluid flow rate is low, and outputs a second signal if the fluid flow rate is high. The first signal and the second signal are output to the microcomputer 70. The changeover switch 50 is set to the first setting when the first signal is output, and supplies the first reference voltage of 0.5 V to the AD converter 60. On the other hand, when the second signal is output, the changeover switch 50 is set to the second setting and supplies the AD converter 60 with the second reference voltage of 4V.

  Further, the amplifier 30 outputs the analog signal Sc to the AD converter 60. The AD converter 60 digitally converts the analog signal Sc with a resolution based on the input first reference voltage or second reference voltage and the number of bits (11 bits in this embodiment). Then, the AD converter 60 outputs a digital signal Sd. The microcomputer 70 calculates fluid information based on the digital signal Sd output from the AD converter 60 and whether the first signal or the second signal is input from the comparator 40.

  Next, the point that the number of bits of the AD converter 60 is small in the fluid detection device 1 according to the present embodiment will be described in detail. In the present embodiment, the AD converter 60 has an overlapping region. For this reason, the AD converter 60 can set the digital signal Sd to one value for different flow speeds of the flow speed a1 and the flow speed a2. Therefore, the AD value can be reduced in accordance with the size of the overlapping area, and the number of bits can be reduced. Referring to FIG. 3, in the measurement range, the digital signal Sd overlaps from “195” to “1802” in both the first setting and the second setting, and the AD value is reduced by this overlap, This has led to a reduction in the number of bits.

For example, assume that it is desired to realize the fluid detection device 1 having a measurement range (output ratio) of 1: 300 and an error of 3% RD. In this case, the AD value is 300 / (3 × 2/100) = 5000 as shown in the above formula (1). In particular, in consideration of disturbance factors, the error needs to be about 1% RD, and the AD value is 300 / (1 × 2/100) = 15000. For this reason, the AD converter needs a 14-bit capability. However, if the output ratio is divided into two, 18 ² = 324> 300. Therefore, 18 / (1 × 2/100) = 900, and the AD converter only needs to have a capacity of at least 10 bits. The overlapping area according to this embodiment is synonymous with dividing the output ratio into two in this way, and can lead to a reduction in the number of bits.

  In particular, in the present embodiment, the minimum analog signal Sc is 12.207 mV and the maximum is 3800 mV, so the measurement range is 12.207: 3800≈1: 311. In the present embodiment, when the measurement range is 1: 311, the AD converter 60 only needs to have an 11-bit capability, and as shown in Expression (1), 311 / (1 × 2/100) = It does not require a 14-bit AD converter with an AD value of 15550. Therefore, the fluid detection device 1 according to the present embodiment can reduce the AD converter 60 by 3 bits, and can reduce the cost and the response of the AD converter 60.

  Further, when switching the reference voltage of the AD converter 60, the microcomputer 70 does not calculate the flow velocity or the like, changes the reference voltage after calculating the flow velocity or the like, and uses the digital signal Sd obtained after the change. We do not have the trouble of calculating the flow velocity again. Therefore, the fluid detection device 1 according to the present embodiment prevents a situation in which the fluid information measurement time becomes long and the responsiveness decreases.

  In this manner, according to the fluid detection measure 1 according to the first embodiment, the AD converter 60 is configured to output the digital signal Sd output at the first setting when the fluid information calculated by the microcomputer 70 is different. , And an overlapping region having the same value as the digital signal Sd output at the time of the second setting. For this reason, a digital signal having one value can be assigned to analog signals obtained at different flow rates. That is, the AD converter 60 outputs a digital signal Sd having a value d with respect to the analog signal Sb having a value b1 obtained by the flow velocity a1, and also outputs an analog signal having a value b2 obtained by a different flow velocity a2. The digital signal Sd having the same value d can be output. As a result, the digital signal Sd can be a single value d for different flow rates a1 and a2, and the AD converter 60 can reduce the AD value according to the size of the overlapping region. This can lead to a reduction in the number of bits. In addition, since the switching between the first setting and the second setting is performed by the output from the comparator 40, the microcomputer 70 does not need to perform the switching after calculating the flow velocity, the flow rate, and the like. Therefore, it is possible to reduce costs while suppressing an increase in measurement time and a decrease in responsiveness.

  Further, the reference voltage is the first reference voltage at the time of the first setting, and the reference voltage is the second reference voltage at the time of the second setting. As described above, when the reference voltage is changed, the resolution of the AD converter 60 is changed. Thereby, for example, at the time of the first setting, the flow sensor 10 outputs the analog signal Sb having the value b1 with respect to the flow velocity a1, and the AD converter 60 inputs the amplified analog signal Sc having the value c1. A digital signal Sd having a value d is output. On the other hand, at the time of the second setting, the flow sensor 10 outputs the analog signal Sb of the value b2 for the flow velocity a2 different from the flow velocity a1, and the AD converter 60 inputs the amplified analog signal Sc of the value c2. It becomes possible to output a digital signal Sd having a value d. In this manner, the digital signal Sd having the same value d is output for the different flow rates a1 and a2. For this reason, the digital signal Sd corresponds to the flow velocities a1 and a2. In this way, by changing the reference voltage, when the fluid information calculated by the microcomputer 70 is different, it is possible to create an overlapping region where the value of the output digital signal Sd is the same. Therefore, it is possible to reduce the cost while suppressing a decrease in responsiveness.

  In addition, since the microcomputer 70 receives the first signal that is a “0” signal and the second signal that is a “1” signal, the determination of the first setting and the second setting is “0”. ”And“ 1 ”only need to be determined, and the program can be simplified, so that the occurrence of bugs can be suppressed. Further, the number of terminals of the microcomputer 70 can be reduced.

  Next, a second embodiment of the present invention will be described. The fluid detection device according to the second embodiment is the same as that of the first embodiment, but is partially different in configuration and operation. Hereinafter, differences from the first embodiment will be described.

  FIG. 4 is a configuration diagram showing the fluid detection device 2 according to the second embodiment. As shown in FIG. 4, in place of the amplifier 30 of the first embodiment, the fluid detection device 2 amplifies the analog signal Sb from the flow sensor 10 with a predetermined amplification factor and adds a predetermined voltage. And an amplifier 31 for supplying to the AD converter 60. The changeover switch 50 has a configuration in which the addition voltage added by the amplifier 31 at the first setting is the first addition voltage, and the addition voltage is the second addition voltage at the second setting. Here, the first addition voltage is 2.5V, and the second addition voltage is 0.5V.

  In addition, the flow sensor 10 according to the second embodiment can detect both forward and reverse flow rates, and the amplifier 31 converts the analog signal Sb from −2.4V to 2.4V in the state before addition after amplification. The added voltage is added to the above voltage. Further, the comparator 40 has a lower threshold value of 0.2V and an upper threshold value of 2.8V. For this reason, the comparator 40 operates as follows. First, it is assumed that the first setting time when the addition voltage is 2.5V. In this state, it is assumed that the comparator 40 receives an analog signal Sc that is from 0.1 V to 2.8 V (from -2.4 V to 0.3 V before addition). In this case, the comparator 40 outputs the first signal, and the changeover switch 50 maintains the first setting. Then, when the analog signal Sc after addition rises to 2.8 V, the comparator 40 switches to output the second signal. As a result, the changeover switch 50 is set to the second setting, and the addition voltage is 0.5V. From the state in which the second signal is output, the comparator 40 continues to output the second signal until the voltage reaches 0.2 V after the addition even if the analog signal Sc decreases. Next, when the analog signal Sc decreases to 0.2 V after addition (−0.3 V before addition), the comparator 40 outputs the first signal.

  In the circuit configuration shown in FIG. 4, the reference voltage is 3V, the reference voltage Vref is 1.5V, the voltage Vmax is 3V, the resistor R1 is 39 kΩ, and the resistor R2 is 6 kΩ. Other configurations are the same as those of the first embodiment.

  In addition, the AD converter 60 has an overlapping area as in the first embodiment. 5A and 5B are diagrams illustrating overlapping regions according to the second embodiment, in which FIG. 5A shows the relationship between the analog signal Sc and the digital signal Sd when the addition voltage is 2.5 V, and FIG. The relationship between the analog signal Sc and the digital signal Sd when the voltage is 0.5 V is shown. In FIG. 5, the measurement range and the normal flow and the reverse flow are also illustrated.

  As shown in FIG. 5, if the reference voltage is 3V and the AD converter 60 is 11 bits, as shown in FIG. 5 (a), the AD converter 60 is in increments of 3000/2048 = 1.46 mV. The analog signal Sc is converted into a digital signal Sd. Further, since the upper limit threshold value is 2.8V, the AD converter 60 converts the analog signal Sc into the digital signal Sd in steps of about 1.46 mV between 0V and 2.8V. In this case, the analog signal Sc of less than 0.1 V is not input to the comparator 40.

  Therefore, when the analog signal Sc of 99.61 mV (about 100 mV) is input, the AD converter 60 outputs the digital signal Sd of “68”, and when the analog signal Sc of 101.07 mV is input, the AD converter 60 outputs the digital signal of “69”. Sd is output. Similarly, when an analog signal Sc of 2499.02 mV is input, the AD converter 60 outputs a digital signal Sd of “1706”, and when an analog signal Sc of 2500.49 mV is input, the AD converter 60 outputs a digital signal Sd of “1707”. To do. The forward flow and the reverse flow are reversed between “1706” and “1707”. When the AD converter 60 receives the analog signal Sc of 2799.32 mV (the same applies to 2800 mV), the AD converter 60 outputs the digital signal Sd of “1911”.

  On the other hand, when the second signal is output from the comparator 40, the changeover switch 50 is set to the second setting. The resolution at this time is the same as that in FIG. 5A and is about 1.46 mV. For this reason, the AD converter 60 converts the analog signal Sc into the digital signal Sd in steps of about 1.46 mV.

  Specifically, the analog signal Sc input to the AD converter 60 in the second setting is in the range of 0.2V to 2.9V. Therefore, as shown in FIG. 5B, the AD converter 60 receives the 200.68 mV analog signal Sc and outputs a digital signal Sd of “137”. Similarly, when the analog signal Sc of 202.15 mV is input, the AD converter 60 outputs the digital signal Sd of “138”. When the AD converter 60 receives the analog signal Sc of 2900.39 mV (actually up to 2900 mV), the AD converter 60 outputs the digital signal Sd of “1980”.

  As described above, the AD converter 60 is used in spite of the difference in the analog signal Sb output from the flow sensor 10, that is, the flow velocity (direction) of the fluid such as normal flow and reverse flow is different. Output the same digital signal Sd within the range of “137” to “1911”, and the AD converter 60 has an overlapping region.

  In addition, since the fluid detection device 2 according to the second embodiment calculates fluid information for both forward and reverse flow velocities, if there is no overlapping region, the AD converter needs a capacity of about 12 bits or more. The fluid detection device 2 according to the second embodiment uses an 11-bit AD converter 60 and reduces the number of bits.

  In this way, according to the fluid detection device 2 according to the second embodiment, as in the first embodiment, it is possible to reduce costs while suppressing an increase in measurement time and a decrease in responsiveness. Further, the occurrence of bugs can be suppressed, and the number of terminals of the microcomputer 70 can be reduced.

  Further, the addition voltage added by the amplifier 31 at the first setting is the first addition voltage, and the addition voltage added by the amplifier 31 at the second setting is the second addition voltage. Thereby, for example, at the time of the first setting, the flow sensor 10 outputs an analog signal Sb having a value b1 with respect to the flow velocity a1. The amplifier 31 amplifies the analog signal Sb having the value b1, and outputs the analog signal Sc having the value c obtained by adding and adding the first addition voltage. The AD converter 60 receives an analog signal Sc having a value c and outputs a digital signal Sd having a value d. On the other hand, at the time of the second setting, the flow sensor 10 outputs an analog signal Sb having a value b2 with respect to the flow velocity a2. The amplifier 31 amplifies the analog signal Sb having the value b2 and adds the second addition voltage. At this time, depending on the value of the added voltage, the value of the analog signal Sc amplified and added can be made the same as the analog signal Sc having the value c. Therefore, the AD converter 60 inputs the analog signal Sc having the value c that has been amplified and added, and outputs the digital signal Sd having the value d. In this manner, the digital signal Sd having the same value d is output for the different flow rates a1 and a2. For this reason, the digital signal Sd having the value d corresponds to the flow velocities a1 and a2. In this way, by changing the addition voltage, it is possible to create an overlapping region where the value of the output digital signal Sd is the same when the fluid information calculated by the microcomputer 70 is different. Therefore, it is possible to reduce the cost while suppressing a decrease in responsiveness.

  Next, a third embodiment of the present invention will be described. The fluid detection device according to the third embodiment is the same as that of the first embodiment, but is partially different in configuration and operation. Hereinafter, differences from the first embodiment will be described.

  FIG. 6 is a configuration diagram showing a fluid detection device 3 according to the third embodiment. As shown in FIG. 6, the fluid detection device 3 includes a heater drive circuit 21 that can change the drive power supplied to the heater 11 instead of the heater drive circuit 20 of the first embodiment. The changeover switch 50 has a configuration in which the driving power supplied by the heater drive circuit 21 at the first setting is a first power value, and the driving power is a second power value different from the first power value at the second setting. It has become. Here, the ratio between the first power value and the second power value is 10: 1.

  FIG. 7 is a block diagram showing an example of the configuration of the heater drive circuit 21 shown in FIG. As shown in FIG. 7, the heater 11 forms a bridge circuit together with the reference resistor Rref and the fixed resistors R4 and R5. Specifically, the reference resistor Rref is connected in series with the fixed resistor R4, and the heater 11 is connected in series with the fixed resistor R5. The connection point between the reference resistor Rref and the fixed resistor R4 and the connection point between the heater 11 and the fixed resistor R5 are input to the operational amplifier. The output of the operational amplifier is input to the base of the PNP transistor Q. A predetermined voltage Vcc is supplied to the emitter of the PNP transistor, and the collector is branched in parallel. One of the parallel branches is connected to the heater 11, and the other is connected to a reference resistor Rref. A changeover switch 50 and resistors Ra and Rb are interposed between the other side branched in parallel and the reference resistor Rref. The changeover switch 50 is configured to switch so that the resistor Ra and the reference resistor Rref are connected in series at the time of the first setting, and to switch so that the resistor Rb and the reference resistor Rref are connected in series at the time of the second setting. . Here, the ratio of the resistance values of the resistor Ra and the resistor Rb is 10: 1. Note that the configuration shown in FIG. 7 is merely an example, and other configurations may be used as long as the drive power can be changed.

  The amplifier 30 according to the third embodiment can output an analog signal Sc of 2.9 V at the maximum, and the comparator 40 has a lower limit threshold value of 0.25 V and an upper limit threshold value of 2.75 V. . The comparator 40 outputs a first signal when an analog signal Sc up to 2.75V is input. Then, when the analog signal Sc rises to 2.75V, the comparator 40 switches to output the second signal. As a result, the changeover switch 50 is set to the second setting. At this time, since the amount of power supplied from the heater drive circuit 21 is 1/10, the analog signal Sc output from the amplifier 30 is about 0.275V. The comparator 40 continues to output the second signal from the state in which the second signal is output until the voltage reaches 0.25 V even if the analog signal Sc decreases. Next, when the analog signal Sc decreases to 0.25 V, the comparator 40 outputs the first signal.

  In the circuit configuration shown in FIG. 6, the reference voltage is 3V, the reference voltage Vref is 1.5V, the voltage Vmax is 3V, the resistor R1 is 50 kΩ, and the resistor R2 is 10 kΩ. Other configurations are the same as those of the first embodiment.

  In addition, the AD converter 60 has an overlapping area as in the first embodiment. FIG. 8 is a diagram illustrating an overlapping region according to the third embodiment. FIG. 8A illustrates the relationship between the analog signal Sc and the digital signal Sd when the drive power ratio is “10”, and FIG. The relationship between the analog signal Sc and the digital signal Sd when the drive power ratio is “1” is shown. In FIG. 8, the measurement range is also illustrated.

  As shown in FIG. 8, when the first signal is output from the comparator 40, the changeover switch 50 is set to the first setting, and the drive power ratio becomes “10”. Here, if the reference voltage is 3V and the AD converter 60 is 11 bits, as shown in FIG. 8A, the AD converter 60 outputs the analog signal Sc in increments of 3000/2048 = about 1.46 mV. It is converted into a digital signal Sd. Since the upper limit threshold is 2.75 V, the AD converter 60 converts the analog signal Sc into the digital signal Sd in steps of about 1.46 mV between 0 V and 2.75 V.

  Therefore, the AD converter 60 outputs a digital signal Sd of “1” when an analog signal Sc of 1.46 mV is input, and outputs a digital signal Sd of “2” when an analog signal Sc of 2.93 mV is input. . Similarly, when an analog signal Sc of 4.39 mV is input, the AD converter 60 outputs a digital signal Sd of “3”. When the AD converter 60 receives an analog signal Sc of 2749.51 mV (the same applies to 2750 mV), the AD converter 60 outputs a digital signal Sd of “1877”. In order to achieve the accuracy of 3% RD, only the analog signal Sc of about 73.24 mV or more, that is, the digital signal Sd of “50” or more is measured, and the digital signal Sd of less than “50” is not measured. It is said.

  On the other hand, when the second signal is output from the comparator 40, the changeover switch 50 is set to the second setting, and the drive power ratio becomes “1”. The resolution at this time is the same as in FIG. 8A, and is about 1.46 mV. For this reason, the AD converter 60 converts the analog signal Sc into the digital signal Sd in steps of about 1.46 mV.

  Specifically, the analog signal Sc input to the AD converter 60 in the second setting is in the range of 0.25V to 2.9V. Therefore, as shown in FIG. 8B, the AD converter 60 outputs the digital signal Sd of “170” when the analog signal Sc of 249.02 mV is input. When the AD converter 60 receives the analog signal Sc of 2900.39 mV (actually up to 2900 mV), the AD converter 60 outputs the digital signal Sd of “1980”.

  As described above, the AD converter 60 outputs the same digital signal Sd within the range of “170” to “1877”, although the fluid flow rates are different. Has overlapping areas.

  Note that the fluid detection device 3 according to the third embodiment has a measurement range of 73.24 mV: 2900 mV × 10≈1: 396. In the third embodiment, when there is no overlapping area, the AD converter needs a capacity of about 15 bits or more, and the fluid detection device 3 according to the third embodiment uses the 11-bit AD converter 60, and the number of bits Have reduced.

  In this way, according to the fluid detection device 3 according to the third embodiment, similarly to the first embodiment, it is possible to reduce costs while suppressing an increase in measurement time and a decrease in responsiveness. Further, the occurrence of bugs can be suppressed, and the number of terminals of the microcomputer 70 can be reduced.

  Further, the driving power supplied to the heater 11 included in the flow sensor 10 is a first power value at the time of the first setting, and a second power value different from the first power value at the time of the second setting. Thereby, for example, at the time of the first setting, the flow sensor 10 outputs an analog signal Sb having a value b with respect to the flow velocity a1. The AD converter 60 receives the amplified analog signal Sc having a value c and outputs a digital signal Sd having a value d. On the other hand, the heater temperature is different in the second setting. For this reason, the flow sensor can output the analog signal Sb having the same value b as the analog signal Sb with respect to the flow velocity a2. The AD converter 60 receives the amplified analog signal Sc having the value c and outputs a digital signal Sd having the value d. In this manner, the digital signal Sd having the same value d is output for the different flow rates a1 and a2. For this reason, the digital signal Sd having the value d corresponds to the flow velocities a1 and a2. As described above, when the fluid information calculated by the microcomputer 70 is different, it is possible to create an overlapping region in which the value of the output digital signal Sd is the same. Therefore, it is possible to reduce the cost while suppressing a decrease in responsiveness.

  In the third embodiment, the driving power supplied to the heater 11 is changed. For this reason, the temperature of the heater 11 is not stable immediately after the change. However, the time required for this stabilization becomes shorter as the flow velocity becomes higher, and it is very short, about 10 msec. Therefore, the time until stabilization is almost no problem in measurement. Further, as in Patent Document 2 and Patent Document 5, it is possible to take a countermeasure such as performing a correction calculation by some method until the temperature of the heater 11 is stabilized.

  Next, a fourth embodiment of the present invention will be described. The fluid detection device according to the fourth embodiment is the same as that of the first embodiment, but is partially different in configuration and operation. Hereinafter, differences from the first embodiment will be described.

  FIG. 9 is a configuration diagram showing a fluid detection device 4 according to the fourth embodiment. As shown in FIG. 9, the fluid detection device 4 includes a first changeover switch 51 and a second changeover switch 52 in place of the changeover switch 50 of the first embodiment. The first changeover switch 51 has a configuration in which the upper limit value of the reference voltage is set as the first upper limit value during the first setting, and the upper limit value of the reference voltage is set as the second upper limit value different from the first upper limit value during the second setting. ing. The second changeover switch 52 has a configuration in which the lower limit value of the reference voltage is set to the first lower limit value at the time of the first setting, and the lower limit value of the reference voltage is set to a second lower limit value different from the first lower limit value at the time of the second setting. ing. The first lower limit value is smaller than the first upper limit value, and the second lower limit value is smaller than the second upper limit value. The voltage difference between the first upper limit value and the first lower limit value is different from the voltage difference between the second upper limit value and the second lower limit value. Specifically, the first upper limit value is 2V, and the first lower limit value is 0V. The second upper limit value is 5V, and the second lower limit value is 1V.

  The amplifier 30 according to the fourth embodiment can output an analog signal Sc of 4.9 V at the maximum, and the comparator 40 has a lower threshold value of 1.3 V and an upper threshold value of 1.7 V. . The comparator 40 outputs the first signal when the analog signal Sc up to 1.7V is output. Then, when the analog signal Sc rises to 1.7V, the comparator 40 switches to output the second signal. As a result, the first and second changeover switches 51 and 52 are set to the second setting. At this time, the comparator 40 continues to output the second signal from the state in which the second signal is output until the voltage reaches 1.3 V even if the analog signal Sc decreases. Next, when the analog signal Sc decreases to 1.3V, the comparator 40 outputs the first signal.

  In the circuit configuration shown in FIG. 9, the reference voltage Vref is 1.5V, the voltage Vmax is 3V, the resistor R1 is 8 kΩ, and the resistor R2 is 52 kΩ. Other configurations are the same as those of the first embodiment.

  In addition, the AD converter 60 has an overlapping area as in the first embodiment. The overlapping area is the same as in the first embodiment. In the first setting, since the upper limit value of the reference voltage is 2V and the lower limit value is 0V, if the AD converter 60 is 11 bits, the resolution is about 0.977 mV to secure 3% RD. Further, an analog signal Sc of 48.828 mV or higher, that is, a digital signal Sd of “50” or higher is set as a measurement target. In the second setting, since the upper limit value of the reference voltage is 5 V and the lower limit value is 1 V, if the AD converter 60 is 11 bits, the resolution is about 1.95 mV, and 3% RD is secured. Therefore, an analog signal Sc of 97.66 mV or higher, that is, a digital signal Sd of “50” or higher is set as a measurement target. In the second setting, since the lower limit threshold is 1.3 V, 3% RD is necessarily secured.

  Furthermore, the fluid detection device 4 according to the fourth embodiment has a measurement range of 48.828 mV: 4900 mV≈1: 100. In the fourth embodiment, when there is no overlapping area, the AD converter needs a capacity of about 12 bits or more, and the fluid detection device 4 according to the fourth embodiment uses the 11-bit AD converter 60, and the number of bits Have reduced.

  In this way, according to the fluid detection device 4 according to the fourth embodiment, as in the first embodiment, it is possible to reduce costs while suppressing the lengthening of measurement time and the decrease in responsiveness. Further, the occurrence of bugs can be suppressed, and the number of terminals of the microcomputer 70 can be reduced.

  In the first setting, the upper limit value of the reference voltage is the first upper limit voltage, the lower limit value of the reference voltage is the first lower limit voltage, and in the second setting, the upper limit value of the reference voltage is the second upper limit voltage. In addition, the lower limit value of the reference voltage is set as the second lower limit voltage. For this reason, even in the AD converter 60 in which the upper limit value and the lower limit value of the reference voltage can be set, cost reduction can be achieved while suppressing a decrease in responsiveness.

  Next, a fifth embodiment of the present invention will be described. The fluid detection device according to the fifth embodiment is the same as that of the first embodiment, but is partially different in configuration and operation. Hereinafter, differences from the first embodiment will be described.

  FIG. 10 is a configuration diagram illustrating a fluid detection device 5 according to the fifth embodiment. As shown in FIG. 10, the fluid detection device 5 includes an amplifier 33 capable of adjusting an amplification factor for amplifying the analog signal Sb, instead of the amplifier 30 of the first embodiment. The changeover switch 50 has a configuration in which the amplification factor of the amplifier 33 is set to the first amplification factor at the first setting, and the amplification factor is set to the second amplification factor different from the first amplification factor at the second setting. Here, the ratio between the first amplification factor and the second amplification factor is 10: 1.

  FIG. 11 is a configuration diagram illustrating an example of a detailed configuration of the amplifier 33 illustrated in FIG. 10. As shown in FIG. 11, the amplifier 33 inputs the analog signal Sb to the inverting input terminal via the resistor R6. The analog signal Sc output from the amplifier 33 is input to the non-inverting input terminal of the amplifier 33 via the resistor Rc or the resistor Rd. The non-inverting input terminal is grounded via a resistor R7. The changeover switch 50 is configured to select either the resistor Rc or Rd and feed back the analog signal Sc output from the amplifier 33 to the non-inverting input terminal of the amplifier 33. With this configuration, the amplifier 33 has a 10: 1 ratio between the gain at the first setting and the gain at the second setting. The amplifier 33 is not limited to this configuration, and may be the same configuration as an instrumentation amplifier.

  The amplifier 30 according to the fifth embodiment can output an analog signal Sc of 2.9 V at the maximum, and the comparator 40 has a lower limit threshold value of 0.25 V and an upper limit threshold value of 2.75 V. . The comparator 40 outputs a first signal when the analog signal Sc up to 2.75V is output. Then, when the analog signal Sc rises to 2.75V, the comparator 40 switches to output the second signal. At this time, since the gain is 1/10 in the second setting, the analog signal Sc output from the amplifier 33 is about 0.275V. The comparator 40 continues to output the second signal from the state in which the second signal is output until the voltage reaches 0.25 V even if the analog signal Sc decreases. Next, when the analog signal Sc decreases to 0.25 V, the comparator 40 outputs the first signal.

  In the circuit configuration shown in FIG. 10, the reference voltage Vref is 1.5V, the voltage Vmax is 3V, the resistor R1 is 50 kΩ, and the resistor R2 is 10 kΩ. Other configurations are the same as those of the first embodiment.

  In addition, the AD converter 60 has an overlapping area as in the first embodiment. The overlapping area is the same as in the third embodiment. If the reference voltage is 3V and the AD converter 60 is 11 bits, the resolution is about 1.46 mV, and an analog signal Sc of 73.24 mV or higher, that is, “50”, in order to secure 3% RD. The above digital signal Sd is a measurement target. In the second setting, since the lower limit threshold is 0.25 V, 3% RD is necessarily secured.

  Furthermore, the fluid detection device 5 according to the fifth embodiment has a measurement range of 73.24 mV: 2900 mV × 10≈1: 396. When there is no overlapping area in the fifth embodiment, the AD converter needs to have a capacity of about 15 bits or more, and the fluid detection device 5 according to the fifth embodiment uses the 11-bit AD converter 60 and sets the number of bits. Reduced.

  As described above, according to the fluid detection device 5 according to the fifth embodiment, as in the first embodiment, it is possible to reduce costs while suppressing an increase in measurement time and a decrease in responsiveness. Further, the occurrence of bugs can be suppressed, and the number of terminals of the microcomputer 70 can be reduced.

  In addition, the amplification factor of the amplifier 33 is the first amplification factor at the first setting, and the amplification factor of the amplifier 33 is the second amplification factor at the second setting. Thereby, for example, at the time of the first setting, the flow sensor 10 outputs an analog signal Sb having a value b1 with respect to the flow velocity a1. The amplifier 33 amplifies the analog signal Sb having the value b1 and outputs the analog signal Sc having the value c. The AD converter 60 receives an analog signal Sc having a value c and outputs a digital signal Sd. On the other hand, at the time of the second setting, the flow sensor 10 outputs an analog signal Sb having a value b2 with respect to the flow velocity a2. The amplifier 33 amplifies the analog signal Sb having the value b2. At this time, the value of the analog signal Sc to be output can be made the same as the analog signal Sc having the value c depending on the value of the amplification factor. Therefore, the AD converter 60 receives the analog signal Sc having the value c and outputs a digital signal Sd. Thus, the same digital signal Sd is output for different flow rates a1 and a2. For this reason, the digital signal Sd corresponds to the flow velocities a1 and a2. Thus, when the fluid information calculated by the microcomputer 70 is different, it is possible to create an overlapping region where the values of the output digital signals are the same. Therefore, it is possible to reduce the cost while suppressing a decrease in responsiveness.

  Next, a sixth embodiment of the present invention will be described. The fluid detection device according to the sixth embodiment is the same as that of the first embodiment, but is partially different in configuration and operation. Hereinafter, differences from the first embodiment will be described.

  FIG. 12 is a configuration diagram illustrating a fluid detection device 6 according to the sixth embodiment. As illustrated in FIG. 12, the fluid detection device 6 includes a second temperature sensor 13 in addition to the temperature sensor (first temperature sensor) 12 of the first embodiment. The fluid detection device 6 includes two changeover switches 53 and 54, two amplifiers 33 and 34, and two AD converters 63 and 64. Similarly to the first embodiment, the temperature sensor 12 outputs an analog signal Sb corresponding to the fluid flow velocity. The second temperature sensor 13 outputs an analog signal Sb ′ for correcting fluid information calculated based on the analog signal Sb from the temperature sensor 12. For the second temperature sensor 13, for example, the right and left thermopiles described in Patent Document 2 are applicable.

  The two changeover switches 50 change the amplification factors of the amplifiers 33 and 34 as in the fifth embodiment. Among these, the first changeover switch 53 is set to the first setting when the first signal is output from the comparator 40 (that is, in the low flow rate range), and is set when the second signal is output from the comparator 40 (that is, the high flow rate range). In the second setting). The second changeover switch 54 is set to the third setting when the first signal is output from the comparator 40 (that is, in the low flow rate range), and when the second signal is output from the comparator 40 (that is, in the high flow rate range). ), The fourth setting.

  As in the fifth embodiment, the amplification factors of the two amplifiers 33 and 34 are changed by the changeover switches 53 and 54. Among these, the first amplifier 33 is, for example, a ratio between an amplification factor when the first changeover switch 53 is set to the first setting and an amplification factor when the first changeover switch 53 is set to the second setting. Is 3.2: 1. In addition, for the second amplifier 33, the ratio between the amplification factor when the second changeover switch 54 is in the third setting and the amplification factor when the second changeover switch 54 is in the fourth setting is 1: 3.2. That is, in the low flow rate region, the first amplifier 33 is switched so that the gain is increased, and the second amplifier 34 is switched so that the gain is decreased. The reverse is true at high flow rates. Note that the ratio of amplification factors may be 2: 1 on one side and 1: 5 on the other side. Here, the reason why the amplification factor is set as described above is as follows. That is, the analog signal Sb output to the temperature sensor 12 increases monotonously with an increase in flow velocity, and the analog signal Sb output to the second temperature sensor 13 increases monotonously with an increase in flow velocity. It is.

  The first AD converter (first analog / digital converter) 63 inputs the analog signal Sc output from the temperature sensor 12 and converts it into a digital signal Sd and outputs it. The second AD converter (second analog / digital converter) 64 receives the amplified analog signal Sc ′ output from the second temperature sensor 13, converts it into a digital signal Sd ′, and outputs it.

  The microcomputer 70 is configured to calculate fluid information based on the first signal or the second signal output from the comparator 40 and the digital signal output from the first AD converter 63. Further, the microcomputer 70 is configured to correct the calculated fluid information based on the first signal or the second signal output from the comparator 40 and the digital signal output by the second AD converter 64.

  Further, the first AD converter 63 calculates the values of the digital signal Sd output at the first setting and the digital signal Sd output at the second setting, although the fluid information calculated by the microcomputer 70 is different. It has overlapping areas that are the same. Similarly, although the fluid information calculated by the microcomputer 70 is different, the second AD converter 64 outputs a digital signal Sd ′ output at the third setting time and a digital signal Sd output at the fourth setting time. It has overlapping areas with the same value as'. The overlapping area is the same as that in each embodiment described above.

  In such a fluid detection device 6, the change in the amplification factor can be reduced. That is, in the fifth embodiment, the amplification factor of one amplifier 33 is changed by 10: 1. In this case, there is a possibility that the measurement accuracy is lowered by a change of the amplification factor of 10 times. However, as in the sixth embodiment, the change of 10 times is increased by 3.2 times, 2 times and 5 times. In other words, the change in the amplification factor of each of the amplifiers 33 and 34 is reduced, and a decrease in measurement accuracy can be suppressed. In the sixth embodiment, the amplification factor has been described. However, the present invention is not limited to this, and the present invention can also be applied to the reference voltage, the addition voltage, and the heater temperature as in other embodiments. Furthermore, in the sixth embodiment, the analog signal Sc is input to the comparator 40, but the present invention is not limited to this, and the analog signal Sc ′ may be used.

  As described above, according to the fluid detection device 6 according to the sixth embodiment, as in the first embodiment, it is possible to reduce costs while suppressing an increase in measurement time and a decrease in responsiveness. Further, the occurrence of bugs can be suppressed, and the number of terminals of the microcomputer 70 can be reduced.

  Moreover, it has the 1st changeover switch 53 and the 2nd changeover switch 54, and the 1st AD converter 63 and the 2nd AD converter 64 each have an overlap area | region. For this reason, it is not necessary to switch the amplification factor, the heater temperature, or the like by a single changeover switch as compared with the case where the amplification factor, the heater temperature, or the like is switched. Therefore, it is possible to suppress a decrease in measurement accuracy due to a large switching by one switching switch.

  As mentioned above, although this invention was demonstrated based on embodiment, this invention is not limited to the said embodiment, You may add a change in the range which does not deviate from the meaning of this invention, and combines each embodiment. Also good. Here, when the embodiments are combined, two comparators 40 and two changeover switches 50 may be provided, and each changeover switch 50 may be changed by each comparator 40, or two changeover switches 50 may be changed by one comparator 40. May be switched. This is because the measurement accuracy can be further increased and the measurement range can be expanded. In addition, when each embodiment is combined, there are a plurality of objects to be changed. Therefore, as described in the fifth embodiment, the change is dispersed to prevent a sudden change, and a decrease in measurement accuracy due to a large switching is suppressed. can do. Further, not only the embodiments may be combined, but the same embodiments may be combined to prevent a large change.

  In the first, third, and fourth embodiments, the amplifier 30 is provided. However, the present invention is not limited to this, and the circuit may be configured by omitting the amplifier 30. Furthermore, the hysteresis range, voltage value, resistance value, and the like described in the above embodiment are not limited to the above, and various changes can be made.

It is a block diagram which shows the fluid detection apparatus which concerns on 1st Embodiment of this invention. It is a figure which shows operation | movement of the comparator shown in FIG. It is a figure explaining an overlap area, (a) has shown the relationship between the analog signal Sc and the digital signal Sd in the case of the reference voltage 0.5V, (b) is the analog signal Sc in the case of the reference voltage 4V, The relationship with the digital signal Sd is shown. It is a block diagram which shows the fluid detection apparatus which concerns on 2nd Embodiment. It is a figure which shows the duplication area | region which concerns on 2nd Embodiment, (a) has shown the relationship between the analog signal Sc and the digital signal Sd in the case of the addition voltage 2.5V, (b) has added voltage 0.5V. The relationship between the analog signal Sc and the digital signal Sd in the case of FIG. It is a block diagram which shows the fluid detection apparatus which concerns on 3rd Embodiment. It is a block diagram which shows an example of a structure of the heater drive circuit shown in FIG. It is a figure which shows the duplication area | region which concerns on 3rd Embodiment, (a) has shown the relationship between the analog signal Sc and the digital signal Sd in the case of drive power ratio "10", (b) is drive power ratio " The relationship between the analog signal Sc and the digital signal Sd in the case of “1” is shown. It is a block diagram which shows the fluid detection apparatus which concerns on 4th Embodiment. It is a block diagram which shows the fluid detection apparatus which concerns on 5th Embodiment. It is a block diagram which shows an example of a detailed structure of the amplifier shown in FIG. It is a block diagram which shows the fluid detection apparatus which concerns on 6th Embodiment.

Explanation of symbols

1 to 6 Fluid detection device 10 Flow sensor 11 Heater 12 Temperature sensor (first temperature sensor)
13 ... 2nd temperature sensor 20, 21 ... heater drive circuit 30, 31, 33, 34 ... amplifier 40 ... comparator 50-54 ... changeover switch (1st changeover switch, 2nd changeover switch)
60, 63, 64 ... AD converter (analog / digital converter, first analog / digital converter, second analog / digital converter)
70: Microcomputer

Claims (7)

A flow sensor that outputs an analog signal according to the flow velocity of the fluid;
An analog-to-digital converter that inputs an analog signal from the flow sensor, converts it to a digital signal, and outputs it,
A comparator that inputs an analog signal and a predetermined voltage from the flow sensor and outputs a first signal or a second signal according to the comparison result;
A changeover switch that has a first setting when the first signal from the comparator is output, and that has a second setting when the second signal from the comparator is output;
A microcomputer that calculates fluid information including at least one of a fluid flow velocity and a flow rate based on the first signal or the second signal output from the comparator and the digital signal output from the analog-digital converter. And comprising
In the analog-digital converter, when the fluid information calculated by the microcomputer is different, the digital signal output at the first setting and the digital signal output at the second setting have the same value. A fluid detection device having an overlapping region. The changeover switch sets a reference voltage, which is a reference when the analog-to-digital converter converts the analog signal to the digital signal, as a first reference voltage at the time of the first setting, and at the time of the second setting. The fluid detection device according to claim 1, wherein the second reference voltage is different from the one reference voltage. In the first setting, the changeover switch sets the upper limit value of the reference voltage to a first upper limit voltage, sets the lower limit value of the reference voltage to a first lower limit voltage smaller than the first upper limit voltage, and The upper limit value of the reference voltage is set as a second upper limit voltage and the lower limit value of the reference voltage is set as a second lower limit voltage smaller than the second upper limit value at the time of setting. Fluid detection device. An amplifier that amplifies the analog signal from the flow sensor and adds a predetermined voltage to supply the analog signal to the analog-digital converter;
The changeover switch is configured such that an addition voltage added by the amplifier is a first addition voltage at the time of the first setting and a second addition voltage different from the first addition voltage at the time of the second setting. The fluid detection device according to any one of claims 1 to 3. An amplifier for amplifying an analog signal from the flow sensor and supplying the analog signal to the analog-digital converter;
The changeover switch sets the amplification factor of the amplifier at the first setting to a first amplification factor, and sets the amplification factor of the amplifier to a second amplification factor different from the first amplification factor at the second setting. The fluid detection device according to any one of claims 1 to 3, wherein the fluid detection device is characterized. The changeover switch sets the drive power supplied to the heater of the flow sensor to a first power value at the time of the first setting and to a second power value different from the first power value at the time of the second setting. The fluid detection device according to claim 1, wherein: The flow sensor outputs a first sensor that outputs an analog signal corresponding to the fluid flow velocity and a correction analog signal that corrects the fluid flow velocity or flow rate calculated based on the analog signal from the first sensor. A second sensor that
The analog-to-digital converter receives the analog signal from the first sensor in the flow sensor, converts the analog signal into a digital signal, and outputs the analog signal. The correction analog signal from the second sensor A second analog-to-digital converter that inputs and converts to a correction digital signal and outputs,
The comparator outputs a first signal or a second signal according to a comparison result between the signal from the first sensor or the second sensor and a predetermined voltage,
The changeover switch has a first setting when the first signal is output from the comparator and a second setting when the second signal from the comparator is output; and A second changeover switch having a third setting when the first signal from the comparator is output and a fourth setting when the second signal from the comparator is output;
When the fluid information calculated by the microcomputer is different, the first analog-digital converter has the same value as the digital signal output at the first setting and the digital signal output at the second setting. And has an overlapping area
When the correction information calculated by the microcomputer is different, the second analog-digital converter has a correction digital signal output at the time of the third setting and a correction digital signal output at the time of the fourth setting. Have overlapping areas with the same value as the signal,
The microcomputer calculates fluid information based on the first signal or the second signal output from the comparator and the digital signal output from the first analog-digital converter, and from the comparator The calculated fluid information is corrected based on the output first signal or the second signal and the correction digital signal output by the second analog-digital converter. The fluid detection device according to claim 6.

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