JP5062720B2 - Flow detection device - Google Patents

Description

  The present invention relates to a flow detection device suitable for detecting a fluid flow.

  Before describing the background art, first, a description method of this specification will be described. Here, the flow rate and the flow velocity of the fluid are collectively referred to as a flow. In general, the flow rate is expressed as the product of the channel cross-sectional area (constant) and the flow velocity, so that the flow rate and the flow velocity can be converted to each other. Further, the name of the resistance element and its resistance value are denoted by the same symbol (for example, the resistance value of the resistance element Ru is denoted as Ru). In addition, the potential and the voltage are not distinguished, and are all described as voltage. Moreover, in any figure, the same code | symbol is attached | subjected to the component which has the same function.

  As shown in FIG. 7, the flow sensor chip 1 used in the flow detection device includes a heating resistor element RH and a pair of temperature sensitive resistance elements Ru and Rd on a silicon base surface using a semiconductor process technology. (Hereinafter, simply referred to as a fluid) in the flow direction F. That is, the temperature sensitive resistance element Ru is arranged on the upstream side with the heating resistance element RH interposed therebetween, and the temperature sensitive resistance element Rd is arranged on the downstream side. Then, utilizing the fact that the thermal coupling state (temperature distribution in the vicinity of the temperature sensitive resistance elements Ru, Rd) between the heat generating resistance element RH and the temperature sensitive resistance elements Ru, Rd changes depending on the flow of the fluid, The flow of the fluid is detected from changes in the resistance values of the temperature resistance elements Ru and Rd. There is also a flow sensor chip (not shown) that does not have the heating resistance element RH and that causes the temperature-sensitive resistance elements Ru and Rd to self-heat.

  In any case, the faster the fluid flow, the more the temperature-sensitive resistance element Ru on the upstream side is cooled and the temperature-sensitive resistance element Rd on the downstream side is heated, and the pair of temperature-sensitive resistance elements Rd and Ru depends on the flow of the fluid. As a result, the electrical resistance changes so as to exhibit an inverse correlation with each other. For example, in the case of a temperature-sensitive resistance element formed of a material such as a metal whose electrical resistance increases as the temperature increases, the resistance value of the temperature-sensitive resistance element Ru decreases and the resistance value of the temperature-sensitive resistance element Rd increases. In order to obtain such characteristics, the temperature sensitive resistance elements Ru and Rd are made of a material such as platinum, nichrome, permalloy, etc. having a particularly significant size and a stable resistance temperature coefficient (hereinafter referred to as TCR). For example, in platinum, TCR is set to about 3000 [ppm / deg].

  For example, as shown in FIG. 8, the flow detection device using such a flow sensor chip has a temperature sensing unit 2 in which two temperature sensing resistance elements Ru and Rd are connected in series and two reference resistance elements R1 and R2 in series. It has a bridge circuit in which the connected reference voltage unit 3 is connected in parallel. The surface of the silicon base is exposed in the flow path so that the temperature sensitive resistance elements Ru and Rd are in contact with the fluid. The reference resistance elements R1 and R2 are mounted on a circuit board 8 to be described later together with other circuit components. The reference resistance elements R1 and R2 are resistors used as, for example, ordinary electric circuit elements, and their TCR is about 100 [ppm / deg] or less. Can be ignored. The constant voltage supply means 4 (power supply unit) applies a constant voltage Vb to the power supply end of the bridge circuit.

  At this time, if the resistance values of the reference resistance elements R1 and R2 are regarded as substantially constant, the voltage at the midpoint of the reference resistance elements R1 and R2 always shows a constant value Vb · R2 / (R1 + R2). Used as a reference voltage. On the other hand, the voltage Vc = Vb · Rd / (Ru + Rd) at the midpoint of the temperature sensitive resistance elements Ru, Rd reflects the change of the temperature sensitive resistance elements Ru, Rd according to the flow of the fluid. The differential amplifier 5 (flow detection unit) to which the voltage Vc and the reference voltage are input outputs a voltage signal (flow signal) corresponding to the difference between them.

  By the way, the temperature-sensitive resistance elements Ru and Rd forming the temperature-sensitive part 2 exhibit a resistance value change according to the flow of the fluid, and also show a resistance value change due to the influence of the temperature of the environment in which they are placed. Since the temperature-sensitive resistance elements Ru and Rd are arranged close to each other, assuming that the entire temperature-sensitive part 2 is placed in the same environment, the temperature of the environment where the temperature-sensitive part 2 is placed (hereinafter referred to as ambient temperature). ) Affects flow detection. In the above example, due to the influence of TCR, for example, as shown by a solid line in FIG. 9, the sensitivity slightly decreases as the ambient temperature increases. This phenomenon becomes an error factor when performing highly accurate measurement.

On the other hand, a heating resistor element RH and a reference resistor element RR are provided on the flow sensor chip, and a bridge circuit is configured by using a fixed resistor connected in series to each of these elements RH and RR. It is proposed to control the heat generation amount of the heating resistor element RH by controlling the drive voltage so as to be balanced, and to calculate the ambient temperature applied to the reference resistor element RR from the drive voltage and the bridge output voltage. (See, for example, Patent Document 1).
JP 2003-106887 A

  Conventionally, in order to solve the problem that the temperature of the environment where the temperature sensing unit 2 is placed affects the detection of the flow, the reference resistance element RR provided on the flow sensor chip for detecting the ambient temperature and the measurement thereof. Means. On the other hand, the inventors focused on the fact that the resistance values of the temperature-sensitive resistance elements Ru and Rd of the temperature-sensing unit 2 change depending on the ambient temperature, and have come to think of obtaining information on the ambient temperature from this resistance value. That is, since the current supplied from the voltage holding unit 13 to the temperature sensing unit 2 has an inverse correlation with the ambient temperature, a resistor is inserted in series between the voltage holding unit 13 and the temperature sensing unit 2. An attempt was made to detect the current flowing from the voltage across the resistor. However, since a means for measuring the voltage across the resistor is newly required, it cannot be said that a particular advantage can be claimed over the conventional configuration described above.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a flow detection device capable of obtaining information on the ambient temperature of the temperature sensing unit with a simple configuration.

  In order to achieve the above-described object, a flow detection device according to the present invention includes a temperature sensing unit that generates a change in electrical resistance in response to a change in temperature distribution caused by a fluid flow, and a power supply unit that supplies power to the temperature sensing unit. A flow detection unit that outputs a flow signal corresponding to the flow, and the temperature sensing unit forms a pair whose electrical resistance changes so as to produce a significant correlation coefficient difference depending on the flow The flow detection unit detects the flow from the state of the electrical resistance of the pair, and particularly according to the temperature of the temperature sensing unit based on the state of power supply to the temperature sensing unit. And a temperature detection unit that outputs a temperature signal.

  Preferably, the temperature detection unit is configured to maintain a power supply state to the temperature sensing unit at a constant voltage. Alternatively, the temperature detection unit includes (a) a power supply terminal, an inverting input terminal, a non-inverting input terminal, and an output terminal. The temperature detection unit outputs the temperature signal from the output terminal and supplies power to the power supply end of the temperature sensing unit. A differential amplifier; (b) a reference voltage supply unit for supplying a reference voltage to a non-inverting input terminal of the differential amplifier; and (c) one end of which is connected to the output terminal of the differential amplifier and the other end of the differential amplifier. A feedback resistor connected to an inverting input terminal of the differential amplifier and a power supply end of the temperature sensing unit is provided.

  Moreover, it is preferable that the temperature sensing unit is provided in the vicinity of the inner wall of the flow path through which the fluid flows so as to contact the fluid. Furthermore, it is preferable to provide a correction unit that corrects the flow signal using the temperature signal in addition to the above-described configuration.

  According to the above configuration, information relating to the ambient temperature of the temperature sensing part can be obtained without providing a dedicated temperature sensing resistor element, and a flow detection error caused by the temperature of the temperature sensing part can be corrected. A flow detection device having a simple configuration can be realized. Further, since the temperature detection unit has both the temperature detection function and the voltage holding function, the configuration of the apparatus can be simplified. Furthermore, since the temperature detector performs temperature detection and voltage holding with a simple configuration, the configuration of the apparatus can be greatly simplified. In addition, since the temperature sensing part is arranged in the vicinity of the inner wall of the flow path, it is possible to adopt a simple shaped flow path, and the structure of the temperature detection part is also extremely simple, thus simplifying the structure of the entire flow detection device. be able to. As a result, the flow detection device can be reduced in size and cost. Further, a flow signal in which a flow detection error due to the temperature of the temperature sensing unit is corrected can be easily obtained.

  In short, according to the present invention, it is possible to provide a flow detection device capable of obtaining information related to the ambient temperature of the temperature sensing unit with a simple configuration, and further to correct a flow detection error caused by the temperature of the temperature sensing unit. It is possible to provide a flow detection device capable of performing the above.

Hereinafter, a flow detection device according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows the overall configuration of a thermal gas flow meter to which the flow detection device of the present invention is applied. The metal main body 6 has a flow path 7 penetrating through the center thereof, and external pipes are connected to the upstream side and the downstream side of the flow path 7, respectively, and fluid flowing through the pipe passes through the flow path 7. To do. A flow sensor chip 1 as shown in FIG. 7 is fixed to the inner wall surface of the flow path 7. An electric circuit is formed on the circuit board 8 fixed to the main body 6 and constitutes the next functional block.

  That is, the power supply unit 4 includes a power supply terminal 9, an AC / DC conversion unit 10, a heater driving unit 11, and a sensor driving unit 12. The power supply terminal 9 connects a power supply line from an external power supply. The AC / DC converter 10 is required when the external power supply is an AC power supply, and converts AC power into DC power using a voltage adjusting transformer, a rectifier, a smoothing capacitor, and the like, and supplies the electric circuit as a whole. A constant voltage circuit for keeping the DC power voltage constant may be incorporated in the power supply unit 4.

  The heater drive unit 11 controls the heat generation of the heating resistor element RH by adjusting the power supplied to the heating resistor element RH. The sensor driving unit 12 has a voltage holding unit 13 and supplies a predetermined constant voltage to the temperature sensing unit 2 and the reference voltage unit 3. The reference voltage unit 3 has the reference resistors R1 and R2 described above. The processing unit 14 includes a flow detection unit 5, a temperature detection unit 15, and a correction unit 16. The correction unit 16 corrects the flow signal from the flow detection unit 5 using the temperature signal from the temperature detection unit 15. The interface unit 17 mediates information between the outside and the processing unit. For example, the interface unit 17 controls external input such as a synchronization signal and calculation parameter setting signal to the processing unit 14 and external output such as a flow rate signal and a flow rate display.

  A first embodiment of the flow detection device of the present invention will be described with reference to FIG. FIG. 2 is an electric circuit diagram of the components relating to the flow detection device of the present invention extracted from FIG. 1 showing the overall configuration of the flowmeter. The series connection of the temperature-sensitive resistance elements Ru and Rd in the temperature-sensitive section 2 and the series connection of the reference resistance elements R1 and R2 in the reference voltage section 3 are connected in parallel to form a bridge. In this bridge, a connection point between the temperature-sensitive resistance element Ru and the reference resistance element R1 is a feeding end, and a connection point between the temperature-sensitive resistance element Rd and the reference resistance element R2 is a grounding end. The temperature-sensitive resistance elements Ru and Rd have the same material, shape, and electrical characteristics (resistance values), and their TCR is about 3000 [ppm / deg].

  The temperature of the upstream temperature sensitive resistance element Ru decreases by ΔT and the temperature of the downstream temperature sensitive resistance element Rd increases by ΔT according to the flow of the fluid to be measured. Along with this, the former resistance value decreases by 3000 ΔT [ppm], and the latter resistance value increases by 3000 · ΔT [ppm]. That is, the temperature-sensitive resistance elements Ru and Rd form a pair in which the electrical resistance changes so as to exhibit an inverse correlation with each other according to the flow of the fluid. The reference resistance elements R1 and R2 have the same material, shape, and electrical characteristics (resistance values), and their TCR is about 100 [ppm / deg] at most. Each resistance value is not affected by temperature and can be regarded as substantially constant.

  The voltage holding unit 13 that always keeps the power supply voltage Vb from the AC / DC conversion unit 10 to the power supply end of the bridge constant, and the temperature detection unit 15 that detects a temperature signal according to the ambient temperature of the temperature sensing unit 2 are: This is realized by two differential amplifier circuits (that is, a differential amplifier 201, a feedback resistance element R3, and a reference voltage supply means 202). The differential amplifier 201 is a general operational amplifier, has a large gain, has a large input impedance, and a small output impedance. DC power is supplied from the AC / DC converter 10 to the power input terminal of the differential amplifier 201. The output terminal of the differential amplifier 201 is connected to the inverting input terminal of the differential amplifier 201 and the power feeding end of the bridge via a feedback resistor element R3. The constant voltage Vr from the reference voltage supply unit 202 is input to the non-inverting input terminal of the differential amplifier 201. The reference voltage supply means 202 is a general constant voltage circuit, and is realized by using, for example, a circuit using a breakdown voltage of a Zener diode, a commercially available IC called a three-terminal regulator, or the like. If the supply voltage of the DC / AC converter 10 is a sufficiently stable constant voltage, the voltage may be appropriately resistance-divided and used as the reference voltage supply means 202.

  Such a differential amplifier circuit has a feedback action of automatically adjusting the output terminal voltage Vt so that the inverting input terminal voltage Vb and the non-inverting input terminal voltage Vr of the operational amplifier 201 become equal, and the power supply voltage Vb to the bridge is provided. Is kept equal to the constant voltage Vr of the reference voltage supply means, and functions as the voltage holding unit 13. In addition, since both the inverting input terminal of the differential amplifier 201 and the correction unit 16 described later have an extremely high input impedance, substantially all of the output current I of the differential amplifier 201 flows to the bridge via the feedback resistance element R3.

The output terminal voltage Vt of the differential amplifier 201 is Vt = Vr + I · R3
= Vr + [Vr / (Ru + Rd) + Vr / (R1 + R2)]. R3
It is expressed. Here, Vr, R1, R2, and R3 are constant, and the resistance values of the temperature-sensitive resistance elements Ru and Rd change according to the flow of the fluid and the ambient temperature of the temperature-sensitive part 2, so that the output terminal voltage Vt is It can be expressed as a function of flow and ambient temperature. Therefore, if the influence of the flow is removed from the output terminal voltage Vt, the output terminal voltage Vt can be used as a temperature signal representing only the ambient temperature.

The simplest method for removing the influence of the flow is to set the respective resistance value changes with respect to the flow of the temperature-sensitive resistance elements Ru and Rd to the same magnitude in the reverse direction. That is, when a flow occurs, if the resistance value of the temperature-sensitive resistance element Ru decreases by ΔRf and the resistance value of the temperature-sensitive resistance element Rd increases by ΔRf, the series connection of the temperature-sensitive resistance elements Ru and Rd is combined. The resistance value is Ru−ΔRf + Rd + ΔRf = Ru + Rd
Since the resistance value changes due to the flow are canceled out, the output terminal voltage Vt is not affected by the flow.

  When the resistance value changes due to the flow of the temperature sensitive resistance elements Ru and Rd do not completely cancel each other, the resistance values of the temperature sensitive resistance elements Ru and Rd are determined by the influence of the fluid flow and the ambient temperature of the temperature sensitive portion 2. Both are affected. However, if the output terminal voltage Vt is measured in advance while changing the flow and the ambient temperature in various ways and correction data as shown in FIG. It is possible to remove the influence of the flow from the output terminal voltage Vt during actual measurement. In this way, the differential amplifier circuit functions as the temperature detecting unit 15 as well as the function of the voltage holding unit 13 described above. In other words, the temperature detection unit 15 has a voltage holding function as well as a temperature detection function.

  The flow detection unit 5 is a differential amplifier composed of an instrumentation amplifier. The midpoint voltage of the reference resistance elements R1 and R2 of the bridge and the midpoint voltage of the temperature sensitive resistance elements Ru and Rd are inputted, and the difference between the two is calculated. Output as a flow signal Vs. That is, the midpoint voltage of the reference resistance elements R1 and R2 is a voltage obtained by resistively dividing the constant voltage Vb into [R1: R2], and is generally Vb / 2 (when R1 = R2). The midpoint voltage of the temperature sensitive resistance elements Ru, Rd is a voltage obtained by resistance-dividing the constant voltage Vb into [Ru: Rd], and is generally Vb / 2 when there is no fluid flow (Ru = Rd). If).

  When resistance value changes −ΔR and ΔR are generated in the temperature-sensitive resistance elements Ru and Rd by the flow, the midpoint voltage of these changes to a voltage obtained by dividing the constant voltage Vb into [Ru−ΔR: Rd + ΔR]. Here, when resistance value changes ΔRT and ΔRT are generated in the temperature-sensitive resistance elements Ru and Rd due to the ambient temperature change of the temperature-sensing unit 2, the midpoint voltage of these is obtained by dividing the constant voltage Vb into [Ru−ΔR + ΔRT: Rd + ΔR + ΔRT]. It changes to voltage and includes errors due to changes in ambient temperature. As described above, the resistance values of the reference resistance elements R1 and R2 are not affected by temperature, and the midpoint voltage does not change.

  The correction unit 16 is realized by a computer program. That is, the flow signal Vs from the flow detection unit 5 is corrected using the temperature signal Vt from the temperature detection unit 15 to remove the influence of the ambient temperature. The correction data is created from the temperature signal Vt and the flow signal Vs measured by variously changing the ambient temperature of the temperature sensing unit 2 and the fluid flow, and is stored in the memory. Similarly, it is desirable to store the data (FIG. 10) for correcting the temperature signal Vt described above in the memory as well.

  As described above, according to the first embodiment of the present invention, information related to the ambient temperature of the temperature sensing unit can be obtained from the state of power feeding to the temperature sensing unit. In addition, since the temperature detection function and the voltage holding function are employed, the configuration of the apparatus can be simplified. Furthermore, if the flow detection device of the present invention is applied to a flow channel with a simple shape in which the temperature sensing unit is arranged near the inner wall of the flow channel, the configuration of the temperature detection unit is very simple, so the configuration of the entire flow detection device is simplified. Can be As a result, the flow detection device can be reduced in size and cost.

  Next, a second embodiment of the present invention will be described with reference to FIG. This embodiment differs from the first embodiment described above only in the configuration of the bridge, and the rest adopts the same configuration. That is, the reference resistance element R1 and the temperature-sensitive resistance element Ru form one series connection, the reference resistance element R2 and the temperature-sensitive resistance element Rd form the other series connection, and these are connected in parallel to form a bridge. The reference resistance elements R1 and R2 arranged on the power supply side constitute the reference voltage unit 303, and the temperature sensitive resistance elements Ru and Rd arranged on the ground side constitute the temperature sensing unit 302. It is desirable that the reference resistance elements R1 and R2 have the same material, shape, and electrical characteristics (resistance value), and the temperature-sensitive resistance elements Ru, Rd have the same material, shape, and electrical characteristics (resistance value).

In this case, the output terminal voltage Vt of the differential amplifier 201 is Vt = Vr + I · R3
= Vr + [Vr / (R1 + Ru) + Vr / (R2 + Rd)]. R3
It is expressed. The resistance values of the temperature sensitive resistance elements Ru and Rd are both affected by the flow of the fluid and the ambient temperature of the temperature sensitive part 2. However, if the output terminal voltage Vt is measured in advance while varying the flow and the ambient temperature in advance and the correction data as shown in FIG. 10 is created, the correction unit 16 described above outputs the actual measurement. It is possible to remove the influence of the flow from the terminal voltage Vt.

  Next, a third embodiment of the present invention will be described with reference to FIG. This embodiment is different from the first embodiment described above only in the specific configuration of the flow detection unit 405 and the method of supplying power to the reference voltage unit 3, and the rest adopts the same configuration. That is, an inexpensive operational amplifier is used for the flow detection unit 405, and power is supplied to the reference voltage unit 3 from the reference voltage supply unit 202. The power supply to the reference voltage unit 3 is performed from the reference voltage supply unit 202 because the resistance values of the reference resistance elements R1 and R2 of the reference voltage unit 3 are relatively limited due to the restriction of the feedback resistance element Rf for the stable operation of the operational amplifier. This is because it is necessary to set a smaller value. At this time, when a current is supplied to the reference voltage unit 3 from the output terminal of the differential amplifier 201 via the feedback resistor element R3 as shown in FIG. 2, the current flowing to the reference voltage unit 3 among the currents flowing through the feedback resistor R3 increases. However, the ratio of the current flowing through the temperature sensing unit 2 becomes relatively small, and the SN ratio of the flow detection is deteriorated.

In order to prevent this, current is supplied only from the output terminal of the differential amplifier 201 to the temperature sensing unit 3 via the feedback resistor R3 as shown in FIG. In this case, the output voltage Vt of the differential amplifier 201 is Vt = Vr + I · R3
= Vr + Vr / (Ru + Rd) · R3
It is expressed.

The simplest method for removing the influence of the flow is to set the change in resistance value with respect to the flow of the temperature-sensitive resistance elements Ru and Rd to the same magnitude in the reverse direction. That is, if the resistance value of the temperature sensitive resistance element Ru decreases by ΔRf and the resistance value of the temperature sensitive resistance element Rd increases by ΔRf when a flow occurs, the combined resistance value of the series connection of the temperature sensitive resistance elements Ru and Rd. Is Ru−ΔRf + Rd + ΔRf = Ru + Rd
Since the resistance value changes cancel each other, the output terminal voltage Vt is not affected by the flow.

  When the resistance value change with respect to the flow of the temperature sensitive resistance elements Ru and Rd does not cancel out, the resistance value of the temperature sensitive resistance elements Ru and Rd has both the influence of the fluid flow and the influence of the ambient temperature of the temperature sensitive portion 2. Also receive. However, if the output terminal voltage Vt is measured in advance while varying the flow and the ambient temperature and the correction data as shown in FIG. 10 is created, the correction unit 16 described above outputs the actual measurement. It is possible to remove the influence of the flow from the terminal voltage Vt.

  Next, a fourth embodiment of the present invention will be described with reference to FIG. This embodiment differs from the above-described third embodiment only in the configuration of the bridge, and the rest adopts the same configuration. That is, the reference resistance element R1 and the temperature-sensitive resistance element Ru form one series connection, the reference resistance element R2 and the temperature-sensitive resistance element Rd form the other series connection, and these are connected in parallel to form a bridge. . The reference resistance elements R1 and R2 arranged on the power supply side constitute the reference voltage unit 503, and the temperature sensitive resistance elements Ru and Rd arranged on the ground side constitute the temperature sensing unit 502. It is desirable that the reference resistance elements R1 and R2 have the same material, shape, and electrical characteristics (resistance value), and the temperature-sensitive resistance elements Ru, Rd have the same material, shape, and electrical characteristics (resistance value).

Here, the output terminal voltage Vt of the differential amplifier 201 is Vt = Vr + I · R3
= Vr + Vr / (R1 + Ru) .R3
It is expressed. The resistance value of the temperature sensitive resistance element Ru is affected both by the influence of the flow of the fluid and the influence of the ambient temperature of the temperature sensing portion 2, but as described above, the output terminal voltage Vt is varied while changing the flow and the ambient temperature in advance. If the correction data as shown in FIG. 10 is created by measuring the above, it is possible to remove the influence of the flow from the output terminal voltage Vt at the time of actual measurement in the correction unit 16 previously prepared. It is.

  Next, a fifth embodiment of the present invention will be described with reference to FIG. In this embodiment, a power supply unit 601 is added in addition to the voltage supply unit 202 in the first embodiment, and the rest of the configuration is the same. That is, when the current to be supplied from the power supply unit 10 to the bridge via the differential amplifier 201 is insufficient (for example, the flow sensor chip does not have the heating resistor element RH and the self-heating of the temperature-sensitive resistor elements Ru and Rd). In this case, a current is supplied from another power supply means 601 to the power supply end of the bridge via the current limiting resistance element. Since the flow detection function and the temperature detection function are substantially the same as those in the first embodiment, detailed description thereof is omitted.

  In the above description, the resistance values of the temperature-sensitive resistance elements Ru and Rd change in reverse with respect to the flow (Ru decreases and Rd increases), but the present invention is not limited to this. For example, the resistance values Ru and Rd both increase according to the flow, but the change in Ru may be small and the change in Rd may be large. In short, the resistance values Ru and Rd do not change in the same way with respect to the flow, and a significant difference that can be detected by comparing the two is produced (that is, a significant correlation coefficient difference is generated). If so, it belongs to the technical scope of the present invention.

  In the above description, for the sake of simplicity, it is assumed that the temperature sensing part is composed of two temperature sensing resistance elements Ru and Rd, but the present invention is not limited to this. For example, a plurality of elements are connected in series or in parallel to form a structure equivalent to the temperature-sensitive resistance element Ru, and a plurality of elements are connected in series or in parallel to form a structure equivalent to the temperature-sensitive resistance element Rd. Even if they exist, they function as a pair exhibiting a change in electrical resistance, and belong to the technical scope of the present invention.

  Further, the present invention is intended to simplify the apparatus, but a temperature-sensitive resistance element for detecting ambient temperature (corresponding to the reference resistance RR of Patent Document 1) provided on the flow sensor chip according to the present invention is provided. It is not a denial to use together. That is, if the present invention is applied to the flow sensor chip shown in FIG. 7 and a temperature-sensitive resistance element for detecting ambient temperature is used, information on the ambient temperature of the temperature-sensing part is obtained from the temperature-sensitive resistance elements Ru and Rd. Information on the ambient temperature at a position away from the temperature sensing unit can be obtained from the temperature sensing resistor element for ambient temperature detection. This makes it possible to find the installation position of the flow sensor chip so that the difference between the two ambient temperatures is the smallest in order to perform more stable measurement, or to measure using the two ambient temperature information for more accurate measurement. It is possible to correct the value. Such an embodiment also belongs to the technical scope of the present invention.

  Furthermore, in the above-described embodiment, the flow sensor chip as illustrated in FIG. 7 has been described as an example. However, the present invention is not limited to this as long as it includes a pair whose electric resistance changes according to the flow of fluid. For example, even a configuration (so-called capillary tube type) in which a temperature sensitive resistance element is formed by winding a metal wire having a large TCR around a small bypass channel provided by branching from a channel is used. Belongs to the technical scope.

  In short, various modifications made without impairing the gist of the present invention still belong to the technical scope of the present invention.

1 is an overall configuration diagram of a thermal flow meter to which a flow detection device according to the present invention is applied. The block diagram of the flow detection apparatus which concerns on 1st embodiment of this invention. The block diagram of the flow detection apparatus which concerns on 2nd embodiment of this invention. The block diagram of the flow detection apparatus which concerns on 3rd embodiment of this invention. The block diagram of the flow detection apparatus which concerns on 4th embodiment of this invention. The block diagram of the flow detection apparatus which concerns on 5th embodiment of this invention. The perspective view which shows typically schematic structure of a flow sensor chip. The block diagram of the conventional flow detection apparatus. The figure which shows the relationship between temperature and a sensitivity. The figure which shows the relationship between temperature and a temperature signal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Flow sensor chip 2 Temperature sensing part 3 Reference voltage part 4 Power supply part 5 Flow detection part 6 Main body 7 Flow path 8 Circuit board 9 Power supply terminal 10 AC / DC conversion part 11 Heater drive part 12 Sensor drive part 13 Voltage holding part 14 Processing part DESCRIPTION OF SYMBOLS 15 Temperature detection part 16 Correction | amendment part 17 Interface part 201 Differential amplifier 202 Reference voltage supply means 302 Temperature sensing part 303 Reference voltage part 405 Flow detection part 502 Temperature sensing part 503 Reference voltage part 601 Power supply means

Claims (3)

A temperature sensing unit that causes a change in electrical resistance in response to a change in temperature distribution caused by a fluid flow, a power supply unit that supplies power to the temperature sensing unit, and a flow detection unit that outputs a flow signal corresponding to the flow The temperature sensing part includes a pair of parts whose electrical resistances change so as to produce a significant correlation coefficient difference according to the flow, and the flow detection part comprises the electrical resistance of the pair In the flow detection device that detects the flow from the state of
Have a temperature detecting section for outputting a temperature signal corresponding to the temperature of the temperature sensing unit based on the state of the power supply to the temperature sensing portion,
The temperature detector is
A differential amplifier that has a power supply terminal, an inverting input terminal, a non-inverting input terminal, and an output terminal, and outputs the temperature signal from the output terminal and feeds power to the feeding end of the temperature sensing unit;
A reference voltage supply unit for supplying a reference voltage to a non-inverting input terminal of the differential amplifier;
A flow detection device comprising: a feedback resistor having one end connected to the output terminal of the differential amplifier and the other end connected to an inverting input terminal of the differential amplifier and a power supply end of the temperature sensing unit. apparatus. The flow detection device according to claim 1 , wherein the temperature sensing unit is disposed in the vicinity of an inner wall of a flow path through which the fluid flows and contacts the fluid. The flow detection device according to claim 1 or 2 ,
The flow detection apparatus further includes a correction unit that corrects the flow signal using the temperature signal.