JP4551416B2 - Flow measuring device - Google Patents

Description

  The present invention relates to the measurement of fluid flow rates.

  There are two main types of methods for measuring the flow rate of fluid. That is, a heating current detection method and a temperature difference detection method.

  In the heating current detection method, the flow rate of the fluid is measured by detecting the heating current required to keep the heater provided in the fluid higher by a certain temperature than the fluid temperature. One temperature difference detection method maintains the temperature of the heating resistor constant, and detects the temperature difference between the upstream temperature detection resistor formed upstream and the downstream temperature detection resistor formed downstream. Detect and measure fluid flow. For example, Japanese Patent Publication No. 5-7659 discloses a fluid flow rate measuring apparatus that employs a temperature difference detection method.

  The two conventional methods described above have the following drawbacks.

  Specifically, a fluid flow rate measuring apparatus that employs a heating current detection method is not suitable for downsizing and it is difficult to measure a flow rate in a small flow rate range.

  The fluid flow rate measurement device that uses the temperature difference detection method can be downsized and measure the flow rate in a small flow rate range. However, as the fluid flow rate increases, the temperature of the upstream temperature detection resistor does not drop any further. In addition, the temperature of the downstream temperature detection resistor starts to decrease. Therefore, the sensitivity decreases at a large flow rate range, and the dynamic range cannot be increased. Moreover, since the temperature of the temperature detection resistor changes due to the flow rate change, the responsiveness is poor.

  An object of the present invention is to provide a fluid flow rate measurement method that can be miniaturized, has high sensitivity and responsiveness, and has a wide dynamic range.

The flow rate measuring device according to the present invention is arranged in a fluid, and is a flow rate measuring device that measures the flow rate of a fluid from the difference between the heat release amount upstream and the heat release amount downstream of a heating element that generates heat. 1st, 2nd, 3rd, 4th, 5th, 6th temperature sensitive resistor which is arrange | positioned from the side to the downstream, and each has the function of the heat generating body which emits heat, and the temperature detection body which detects temperature And a control circuit for controlling supply of electric power for generating heat from the temperature sensitive resistor. The first, second, fifth, and sixth temperature sensitive resistors are connected to a constant current source or a constant voltage source, and the second, third, fourth, and fifth temperature sensitive resistors are Connected to the power supply,
The control circuit includes a first comparison circuit that compares the temperatures of the first and sixth temperature sensitive resistors, a second comparison circuit that compares the temperatures of the second and fifth temperature sensitive resistors, A plurality of switches arranged between a power source and the second, third, fourth, and fifth temperature sensitive resistors, the temperature comparison result by the first comparison circuit and the temperature comparison by the second comparison circuit Based on the result, an opening / closing operation is performed to supply power from the power source to one of the first, second, third, and fourth temperature sensitive resistors, and the first And the switch for making the temperatures of the second and fifth temperature sensitive resistors equal , and further making the temperatures of the first and sixth temperature sensitive resistors equal. Based on the difference between the power supplied to the temperature sensitive resistor and the difference between the power supplied to the second and fifth temperature sensitive resistors. The flow rate is measured. This achieves the above object.

  Preferably, a heating resistor is further provided between the third and fourth temperature sensitive resistors, and the circuit is configured so that an average temperature of the first temperature sensitive resistor and the sixth temperature sensitive resistor is preset. The electric power supplied to the heating resistor may be controlled so that the temperature is set.

  The circuit may change the preset temperature based on the temperature of the fluid.

  Among the six temperature sensitive resistors provided from the upstream side to the downstream side of the fluid, the difference in power supplied to the second and fifth temperature sensitive resistors changes greatly when the fluid flow rate is small, and the third, The difference in power supplied to the temperature sensitive resistor 4 increases greatly when the fluid flow rate is large. Therefore, it is possible to measure the flow rate with high sensitivity over a wide flow range. In addition, since the temperatures of the upstream and downstream temperature sensitive resistors are feedback-controlled, the responsiveness is improved.

  Even if the flow rate is increased, the temperature of the first to sixth temperature sensitive resistors can be kept high, which is particularly effective for increasing sensitivity and increasing the dynamic range at a large flow rate. In addition, since the temperatures of the upstream and downstream temperature detectors are kept constant, the responsiveness is improved.

  Even if the temperature of the fluid changes, the temperature difference between the fluid and the apparatus is kept constant, so that the flow rate can be measured even when the temperature of the fluid changes.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. In the drawings, the same reference numerals are assigned to components having the same function.

(Embodiment 1)
Figure 1 shows the structure of the measurement portion of the fluid flow measuring apparatus of the first embodiment. The fluid flow measuring device includes a thin-walled portion 3 formed on a silicon substrate 1 and an upstream temperature detection resistor 5 as a temperature sensor from the upstream side, and a first heating resistor formed of a temperature sensitive material such as platinum. 68, a second heating resistor 69, a third heating resistor 70 and a fourth heating resistor 71, and a downstream temperature detection resistor 6 as a temperature sensor . In addition, although distinguished from "temperature detection resistor" and "heat generating resistor", these can be considered as the same element called "temperature sensitive resistor". That is, the temperature sensitive resistor has two functions: a function of detecting temperature and a function of generating heat. A wiring portion 9 is connected to each of the resistors 5, 68, 69, 70, 71 and 6, and a pad portion 10 is connected to one end of the wiring portion 9. The pad portion 10 is used for wire bonding or the like for connection with an external circuit. The thin portion 3 is formed of insulating layers 7 and 8 and resistors 5 and 6 formed therebetween. Silicon on the back surface side of the thin portion 3 is removed by etching to form a cavity.

FIG. 2 is a circuit diagram of a fluid flow rate measuring device including six resistors according to the first embodiment. A constant current source 13 is connected to the upstream temperature detection resistor 5 (Rsu) and the downstream temperature detection resistor 6 (Rsd), and a constant current Is is supplied. The both-ends voltage (Vsu) of the upstream temperature detection resistor 5 and the both-ends voltage (Vsd) of the downstream temperature detection resistor 6 are input to the −input terminal and the + input terminal of the comparator 72, respectively. The output of the comparator 72 is high when the temperature of the upstream temperature detection resistor 5 is lower than the temperature of the downstream temperature detection resistor 6 (ie, Vsu <Vsd), and vice versa (ie, Vsu> Vsd). In the case of). The output of the comparator 72 is connected to the switches 74 and 75.

  A constant current source 80 for supplying a constant current Is is connected to the first heating resistor 68 and the fourth heating resistor 71. The both-end voltage 82 (Vh1) of the first heating resistor 68 and the both-end voltage 85 (Vh4) of the fourth heating resistor 71 are input to the −input terminal and the + input terminal of the comparator 73, respectively. The output of the comparator 73 is high when the temperature of the first heating resistor 68 is lower than the temperature of the fourth heating resistor 71 (ie, Vh1 <Vh4), and vice versa (ie, Vh1> Vh4). ) Is low. The output of the comparator 73 is connected to switches 76, 77, 78, 79. One end of the switch 74 is connected to the power supply 11, and the other end is connected to one end of the switch 78 and one end of the switch 79. The other end of the switch 78 is connected to the second heating resistor 69, and the other end of the switch 79 is connected to the first heating resistor 68. One end of the switch 75 is connected to the power supply 11, and the other end is connected to one end of the switch 76 and one end of the switch 77. The other end of the switch 76 is connected to the fourth heating resistor 71, and the other end of the switch 77 is connected to the third heating resistor 70. The voltage at the output terminal 16 of the comparator 72 and the output terminal 81 of the comparator 73 is the output voltage.

Next, the operation of the circuit of FIG. 2 will be described. When fluid flows from the upstream side, the temperature of the upstream temperature detection resistor 5 is lower than the temperature of the downstream temperature detection resistor 6, and the relationship between the voltages at both ends is Vsu <Vsd. At this time, since the output of the comparator 72 is at a high level, the switch 74 is turned on and the switch 75 is turned off. At this time, the temperature of the first heating resistor 68 is lower than the temperature of the fourth heating resistor 71, and the relationship between the voltages at both ends is Vh1 <Vh4. Therefore, the output of the comparator 73 becomes high level, the switches 76 and 78 are turned on, and the switches 77 and 79 are turned off. Then, the second heating resistor 69 is connected to the power supply 11.

  When a current flows through the second heating resistor 69, heat is generated by Joule heat, and the temperature of the first heating resistor 68 in the vicinity is raised. When the temperature of the first heating resistor 68 rises and becomes higher than the temperature of the fourth heating resistor 71, the relationship between the voltages at both ends becomes Vh1> Vh4. At this time, the output of the comparator 73 is at a low level, the switches 76 and 78 are turned off, the switches 77 and 79 are turned on, and the first heating resistor 68 and the power source 11 are connected.

  When a current flows through the first heating resistor 68, heat is generated by Joule heat, and the temperature of the upstream temperature detection resistor 5 in the vicinity is raised. When the temperature of the upstream temperature detection resistor 5 rises and becomes higher than the temperature of the downstream temperature detection resistor 6, the relationship between the voltages at both ends becomes Vsu> Vsd. As a result, the output of the comparator 72 becomes low level, the switch 74 is turned off, and the switch 75 is turned on. Then, the third heating resistor 70 and the power source 11 are connected, and a current flows through the third heating resistor 70.

  The third heating resistor 70 generates heat due to Joule heat and raises the temperature of the fourth heating resistor 71 in the vicinity. When the temperature of the fourth heating resistor 71 rises and becomes higher than the temperature of the first heating resistor 68, the relationship between the voltages at both ends becomes Vh1 <Vh4. At this time, the output of the comparator 73 becomes high level, the switches 77 and 79 are turned off, and the switches 76 and 78 are turned on. Then, the fourth heating resistor 71 and the power source 11 are connected, and a current flows through the fourth heating resistor 71.

  The fourth heating resistor 71 generates heat due to Joule heat and raises the temperature of the downstream temperature detection resistor 6 in the vicinity. When the temperature of the downstream temperature detection resistor 6 rises and becomes higher than the temperature of the upstream temperature detection resistor 5, the relationship between the voltages at both ends becomes Vsu <Vsd. At this time, the output of the comparator 72 is at a high level, the switch 75 is turned off, the switch 74 is turned on, and the initial state is restored.

  Thus, the operation of switching the power supply 11 to the first, second, third, and fourth heating resistors in order by the switches 74, 75, 76, 77, 78, and 79 is repeated, and the upstream temperature detection resistor The temperature of the body 5 and the temperature of the downstream temperature detection resistor 6, and the temperature of the first heating resistor 68 and the temperature of the fourth heating resistor 71 are controlled to be equal.

FIG. 3 shows the relationship between the terminal voltages of the resistors 68 to 71 (FIG. 2 ) and the voltages of the output terminals 16 and 81 (FIG. 2 ). In the figure, the pulse 86 represents the first output voltage 16 (Vout1) in FIG. The pulse 87 indicates the second output voltage 81 (Vout2). The pulse 88 indicates the voltage across the second heating resistor 69 (Vh2), the pulse 89 indicates the voltage across the first heating resistor 68 (Vh1), and the pulse 90 indicates the third heating resistor 70. , And a pulse 91 indicates a voltage across the fourth heating resistor 71 (Vh4). As apparent from the timing shown in FIG. 3 , when both the pulse 86 (Vout1) and the pulse 87 (Vout2) are at a high level, the pulse 88 (Vh2) is at a high level. After that, the high level state moves in the order of Vh1, Vh3, Vh4, and returns to Vh2.

FIG. 4 shows the relationship between Vout1, Vout2 and Vh1 to Vh4. When the fluid is flowing from the upstream side, the time during which the temperature of the upstream temperature detection resistor 5 is lower than the temperature of the downstream temperature detection resistor 6 is longer, so the time during which the output of the comparator 72 is at the high level (t1 ) Is longer than the time (t2) at the low level. Further, since the time when the temperature of the first heating resistor 68 is lower than the temperature of the fourth heating resistor 71 is longer, the time (t3) when the output of the comparator 73 is at the high level is the time when it is at the low level. It becomes longer than (t4). Each difference (or ratio) increases as the fluid flow rate increases. In the case of backflow, the magnitude relationship is reversed.

As shown in FIG. 5 , the analog output voltages 94 and 95 are obtained by passing the output voltages 86 (Vout1) and 87 (Vout2) through the low-pass filters 92 and 93, respectively. The analog output voltages 94 and 95 take values corresponding to the duty ratios [t1 / (t1 + t2 )] and [t3 / (t3 + t4)] of the output voltages 86 and 87. The final output voltage 97 is obtained by adding the analog output voltages 94 and 95 by the adder circuit 96. Therefore, by measuring the voltage 97, the fluid flow rate can be known.

FIG. 6 shows a graph of the final output voltage 97 obtained from the two output voltages 94, 95. The output voltage 94 (Vout1) obtained based on the temperature magnitude relationship between the upstream temperature detection resistor 5 and the downstream temperature detection resistor 6 is obtained from the first heating resistor 68 and the fourth heating resistor 71. The change is larger in a smaller flow rate region than the output voltage 95 (Vout2) obtained based on the temperature magnitude relationship. Conversely, in the large flow rate region, the output voltage 94 (Vout1) is saturated, whereas the output voltage 95 (Vout2) varies greatly. This is because the upstream temperature detection resistor 5 and the downstream temperature detection resistor 6 are located away from the high temperature portion (center portion) on the thin portion 3, and the temperature change is likely to occur at a small flow rate. This is because the first and fourth heat generating resistors 68 and 71 are closer to the high temperature portion and the temperature change is likely to occur at a large flow rate. By adding the two output voltages, a high-sensitivity output voltage 97 can be obtained regardless of whether the flow rate is small or large. For comparison, the conventional output voltage 98 is indicated by a dotted line.

  As described above, according to the present embodiment, a high-sensitivity output in a small flow region and a high-sensitivity output in a large flow region are added to obtain an output, so that a high-sensitivity output can be obtained over a wide range and the dynamic range is expanded. To do. Further, since the temperatures of the upstream temperature detection resistor 5, the downstream temperature detection resistor 6, the first heating resistor 68, and the fourth heating resistor 71 are feedback-controlled, the conventional open loop method is used. Responsiveness is improved.

(Embodiment 2 )
Figure 7 shows a process for digitally outputting the output voltage 86 described in FIG. 5 (Vout1) and 87 (Vout2). When the output voltages 86 and 87 and the high-frequency pulse signal 99 are multiplied by the multipliers 100 and 101, the high-frequency pulses 102 and 103 remain only when the output voltages 86 and 87 are at the high level (between t1 and t3 in FIG. 3 ). . The number of pulses of the high-frequency pulses 102 and 103 is counted by the pulse counters 104 and 105 for a fixed time, and the result is added by the adder circuit 106, whereby a digital output 107 is obtained.

By adopting such a configuration, the same effects as those of the first embodiment can be obtained, and the connectivity with the CPU can be improved.

(Embodiment 3 )
In the first embodiment, the duty ratios [t1 / (t1 + t2)] and [t3 / (t3 + t4)] are adopted as outputs, but the duty ratio difference [(t1-t2) / (t1 + t2)] , [(T3-t4) / (t3 + t4)] can be output.

FIG. 8 shows a process for outputting the duty ratio difference. First, the output voltage 86 (Vout1) is passed through the low-pass filter 92, and an analog voltage 94 is obtained. Further, the output voltage 86 (Vout1) is inverted by the inverting circuit 108 and further passed through the low-pass filter 110 to obtain the analog voltage 112. By subtracting these analog voltages 94 and 112 by the subtraction circuit 114, an analog voltage 116 corresponding to the duty ratio difference [(t1-t2) / (t1 + t2)] is obtained.

  On the other hand, the output voltage 87 (Vout2) is passed through the low-pass filter 93, and an analog voltage 95 is obtained. Further, the output voltage 87 (Vout2) is inverted by the inverting circuit 109 and further passed through the low-pass filter 111 to obtain the analog voltage 113. By subtracting these analog voltages 95 and 113 by the subtraction circuit 115, an analog voltage 117 corresponding to the duty ratio difference [(t3-t4) / (t3 + t4)] is obtained.

  The final output voltage 97 is obtained by adding the analog voltages 116 and 117 obtained as described above by the adding circuit 96.

Even with such a configuration, the same effect as in the first embodiment can be obtained, and the offset output (output at a flow rate of 0) can be reduced to 0, so that the sensitivity is further improved.

(Embodiment 4 )
Figure 9 shows another process for the output voltage 86 (Vout1) and 87 described in FIG. 5 (Vout2) to a digital output.

  First, when the multiplier 100 multiplies the output voltage 86 (Vout1) by the high frequency pulse signal 99, the high frequency pulse 102 remains only when the output voltage 86 is at a high level. The number of pulses 102 is counted by the pulse counter 104 for a certain time. Further, when the output voltage 86 (Vout1) is inverted by the inverting circuit 118 and multiplied by the high frequency pulse signal 99 in the multiplier 120, the high frequency pulse 122 remains only when the inverted voltage is at a high level. The pulse counter 124 counts the number of pulses 122 for a certain time. The subtraction circuit 126 performs a subtraction process on the pulse counting result obtained as described above.

  On the other hand, when the multiplier 101 multiplies the output voltage 87 (Vout2) by the high frequency pulse signal 99, the high frequency pulse 103 remains only when the output voltage 87 is at a high level. The number of pulses 103 is counted by a pulse counter 105 for a certain time. Further, when the output voltage 87 (Vout2) is inverted by the inverting circuit 119 and multiplied by the high frequency pulse signal 99 in the multiplier 121, the high frequency pulse 123 remains only when the inverted voltage is at a high level. The number of pulses 123 is counted by the pulse counter 125 for a certain time. The count result of the pulses obtained as described above is subtracted by the subtraction circuit 127.

  Each subtraction result obtained as described above is added by the adder circuit 106, whereby a final digital output 107 is obtained.

Even with this configuration, the same effects as those of the third embodiment can be obtained, and the connectivity with the CPU can be improved.

In the circuit configuration of Embodiment 1, 2, 3, 4 of the embodiment, the upstream temperature sensing resistor 5 and the downstream temperature sensing resistor 6, the first heating resistor 68 and the fourth heating resistor 71, a constant current The supplied constant current sources 13 and 80 were used. However, similar results can be obtained using a constant voltage source that applies a constant voltage.

(Embodiment 5 )
FIG. 10 shows the configuration of the measurement unit of the fluid flow measurement device according to the fifth embodiment. In the fluid flow measuring device of the fifth embodiment, the central heating resistor 4 is formed between the second heating resistor 69 and the third heating resistor 70. In the figure, since the wiring part 9 and the pad part 10 are the same as those in FIG. 1 , their description is omitted. The central heating resistor 4 (Rh), upstream temperature detection resistor 5 (Rsu), and downstream temperature detection resistor 6 (Rsd) constitute a constant temperature circuit, and the upstream temperature detection resistor 5 and downstream temperature detection. The power supplied to the central heating resistor 4 is controlled so that the average temperature of the resistor 6 is constant. A constant temperature circuit diagram is shown in FIG .

FIG. 11 is a circuit diagram of the fluid flow rate measuring device including the resistors 4, 5 and 6. A constant current source 13 is connected to the upstream temperature detection resistor 5 (Rsu) and the downstream temperature detection resistor 6 (Rsd), and a constant current Is is supplied. The voltage across the resistors Rsu5 and Rsd6 (Vsu, Vsd) is input to the adder circuit 15. When the gain of the adder circuit 15 is G, the output voltage Vadd of the adder circuit is expressed by the following formula 1.

The voltage 19 (Vt) obtained by dividing the constant voltage 12 (Vc) by the fixed resistors R1 and R2 is compared with the output voltage Vadd of the adder circuit 15, and the power transistor 20 causes the heating resistor 4 to equalize both. Is supplied with power. Here, a voltage Vt obtained by dividing the constant voltage Vc is expressed by the following formula 2.

Therefore, when Vt = Vadd, the following equation 3 is obtained from the equations 1 and 2.

If the upstream temperature detection resistor 5 and the downstream temperature detection resistor 6 have a resistance value at 0 ° C. of Rs0, the resistance temperature coefficient is αs, and the temperatures are Tsu and Tsd, respectively, the upstream temperature detection resistor 5 and the downstream temperature detection resistor The both-end voltages Vsu and Vsd of the body 6 are obtained as shown in the following equations 4 and 5, respectively. As a result, the following equation 6 is obtained.

From the above formulas 3 and 6, the following formula 7 is obtained.

Since all the terms on the right side of Equation 7 are constants, the right side is a constant. Therefore, by configuring the circuit shown in FIG. 11 , the average value of the temperature (Tsu) of the upstream temperature detection resistor 5 and the temperature (Tsd) of the downstream temperature detection resistor 5 can be kept constant.

となる。数８から明らかなように、出力電圧Ｖoutは、上流温度検出抵抗体５の温度(Ｔsu)と下流温度検出抵抗体６の温度(Ｔsd)の差に比例することが理解される。 Further, referring to FIG. 11 , a differential amplifier 17 is connected to the upstream temperature detection resistor 5 and the downstream temperature detection resistor 6. The differential amplifier 17 outputs the potential difference between the both-end voltages Vsu and Vsd of the upstream temperature detection resistor 5 and the downstream temperature detection resistor 6 from the terminal 16 as the output voltage Vout. Specifically, the output voltage Vout is as shown in the following equation (8).

It becomes. As is apparent from Equation 8, it is understood that the output voltage Vout is proportional to the difference between the temperature (Tsu) of the upstream temperature detection resistor 5 and the temperature (Tsd) of the downstream temperature detection resistor 6.

  In order to obtain a flow rate from the output voltage Vout, a flow rate-output voltage table is generally prepared in advance and this table may be referred to. The table is stored in a memory (not shown) included in the fluid flow measuring device. The operation referring to the table is performed by a central processing unit (not shown) of the fluid flow rate measuring device. Instead of using a table, a conversion formula in which the flow rate is given as an output value using the output voltage Vout as a variable may be used.

FIG. 12 is a graph of temperature changes of the upstream temperature detection resistor 5 and the downstream temperature detection resistor 6 according to the fluid flow rate. This figure is created based on the result of simulation by the thermal network method. A curve 21 and a curve 22 indicate the temperature of the upstream temperature detection resistor 5 and the temperature of the downstream temperature detection resistor 6 according to the present embodiment, respectively. On the other hand, curves 23 and 24 indicate the temperature of the upstream temperature detection resistor 5 and the temperature of the downstream temperature detection resistor 6 in the conventional example, respectively. In the conventional example, the temperature of the upstream temperature detection resistor 5 and the temperature of the downstream temperature detection resistor 6 decrease as the flow rate increases, and the average temperature also decreases with the flow rate. As described in relation to Equation 7, in this embodiment, the temperature of the upstream temperature detection resistor 5 and the average temperature of the downstream temperature detection resistor 6 are controlled to be constant. Accordingly, when the temperature of the upstream temperature detection resistor 5 (curve 21) decreases with the flow rate, the temperature of the downstream temperature detection resistor 6 (curve 22) increases with the flow rate.

  In the present embodiment, the temperature drop due to the flow rate of the upstream temperature detection resistor 5 (curve 21) is smaller than the temperature drop due to the flow rate of the upstream temperature detection resistor 5 in the conventional example (curve 23). Therefore, when the flow rate is increased to some extent, the temperature of the upstream temperature detection resistor 5 in the present invention is higher than the temperature of the upstream temperature detection resistor 5 in the conventional example. From the viewpoint of the measurable temperature, for example, when the lower limit of the measurable temperature is assumed to be 65 ° C., conventionally, only a flow rate of about 60 g / s can be measured as shown by the curve 23. However, according to Embodiment 1, it is possible to measure up to about 200 g / s. Therefore, the temperature of the upstream temperature detection resistor 5 in the first embodiment is allowed to change to a larger flow rate than in the conventional example.

FIG. 13 is a graph showing the flow rate dependency of the difference between the temperature of the upstream temperature detection resistor 5 and the temperature of the downstream temperature detection resistor 6. In the figure, a curve 25 indicates a temperature difference between the upstream temperature detection resistor 5 and the downstream temperature detection resistor 6 in the first embodiment. On the other hand, a curve 26 shows a temperature difference between the upstream temperature detection resistor 5 and the downstream temperature detection resistor 6 in the conventional example. As described above, the temperature of the upstream temperature detection resistor 5 in the first embodiment can be changed to a larger flow rate, and the temperature of the downstream temperature detection resistor 6 of the present invention increases with the flow rate. . Therefore, the temperature difference becomes larger than the conventional one, and shows a large flow rate dependency up to a larger flow rate.

According to the circuit of FIG. 11 , the average temperature of the upstream temperature detection resistor 5 and the downstream temperature detection resistor 6 can be kept constant. Further, by controlling the temperature of the upstream temperature detection resistor 5 and the downstream temperature detection resistor 6 equally by the circuit of FIG. 2, the temperature of the resistors 5 and 6 is kept constant in the entire flow rate range. Become.

  As described above, according to the configuration of the present embodiment, the temperature of the upstream temperature detection resistor 5 and the downstream temperature detection resistor 6 is kept constant regardless of the flow rate, so that the dynamic range can be expanded. . Further, since the temperature change due to the flow rate change does not occur, the responsiveness is improved. Furthermore, since the temperature of the resistor can be maintained at 100 ° C. or higher, when a water droplet or the like adheres, it can be immediately evaporated, and the drift of characteristics due to moisture adhesion can be reduced.

(Embodiment 6 )
FIG. 14 shows the configuration of the measurement unit of the fluid flow measurement device according to the sixth embodiment. In the figure, since the wiring part 9 and the pad part 10 are the same as those in FIG. 1 , their description is omitted.

In the sixth embodiment, a fluid temperature detection resistor 55 (Ra) for detecting the temperature of the fluid is formed on the silicon chip 1. The fluid temperature detection resistor 55 is formed at a position away from the thin portion 3 so as not to be thermally affected by the heating resistors 4, 68, 69, 70 and 71. Silicon on the back surface of the fluid temperature detection resistor 55 may be removed by etching, and the fluid temperature detection resistor 55 may be formed on the second thin portion.

The circuit shown in FIG. 16 in the seventh embodiment is configured using the fluid temperature detection resistor 55. Thereby, the temperature of the upper stream side temperature sensing resistor 5 and (Tsu) value the average value is dependent on the fluid temperature Ta between the temperature of the downstream temperature sensing resistor 6 (Tsd), when the high fluid temperature Ta is The average temperature of the upstream temperature detection resistor 5 and the downstream temperature detection resistor 6 is also high. On the other hand, when the fluid temperature Ta is low, the average temperature of the upstream temperature detection resistor 5 and the downstream temperature detection resistor 6 is also controlled to be low. Fluid temperature Ta and the upstream side temperature sensing resistor 5, the relationship between the average temperature of the downstream temperature sensing resistor 6 can be adjusted by the circuit constants R1 and R2 having in 12 below.

  By adopting such a configuration and control, it is possible to compensate for the change in characteristics when the temperature of the fluid changes, and the temperature characteristics are improved.

(Embodiment 7)
FIG. 15 shows a configuration of a measurement unit of the fluid flow measurement device according to the seventh embodiment. In the fluid flow rate measurement device according to the seventh embodiment, a fluid temperature detection resistor 55 that detects the temperature of the fluid is formed on the silicon chip 1. The fluid temperature detection resistor 55 is formed at a position away from the thin portion 3 so as not to be thermally affected by the heating resistor 4. Silicon on the back surface of the fluid temperature detection resistor 55 may be removed by etching, and the fluid temperature detection resistor 55 may be formed on the second thin portion.

FIG. 16 is a circuit diagram of a fluid flow rate measuring device including the fluid temperature detection resistor 55 according to the seventh embodiment. In this circuit, the voltage 19 (Vt) is expressed by Equation 9 .

When control is performed so that Vadd in Expression 1 is equal to Vt in Expression 9 , the following Expression 10 is established.

数１０および数６から、下記数１２が成り立つ。

数１２の右辺に流体温度検出抵抗体５５の温度Ｔaが含まれているため、右辺全体はＴaに依存した値となる。よって、上流側温度検出抵抗体５の温度（Ｔsu）と下流側温度検出抵抗体６の温度（Ｔsd）との平均値も流体温度Ｔaに依存した値となり、流体温度Ｔaが高いときは上流側温度検出抵抗体５と下流側温度検出抵抗体６の平均温度も高く、流体温度Ｔaが低いときは上流側温度検出抵抗体５と下流側温度検出抵抗体６の平均温度も低くなる。流体温度Ｔaと、上流側温度検出抵抗体５および下流側温度検出抵抗体６の平均温度との関係は、数１２中の回路定数Ｒ１やＲ２により調整できる。 When the resistance value of the fluid temperature detection resistor 55 at 0 ° C. is Ra0 and the resistance temperature coefficient is αa, when the temperature of the fluid (and the resistor 55) is Ta,

From Equation 10 and Equation 6 , the following Equation 12 holds.

Since the temperature Ta of the fluid temperature detection resistor 55 is included in the right side of Equation 12, the entire right side is a value dependent on Ta. Therefore, the average value of the temperature (Tsu) of the upstream temperature detection resistor 5 and the temperature (Tsd) of the downstream temperature detection resistor 6 also depends on the fluid temperature Ta, and when the fluid temperature Ta is high, the upstream side The average temperature of the temperature detection resistor 5 and the downstream temperature detection resistor 6 is also high, and when the fluid temperature Ta is low, the average temperature of the upstream temperature detection resistor 5 and the downstream temperature detection resistor 6 is also low. The relationship between the fluid temperature Ta and the average temperature of the upstream temperature detection resistor 5 and the downstream temperature detection resistor 6 can be adjusted by the circuit constants R1 and R2 in Equation 12 .

  By adopting such a configuration and control, it is possible to compensate for the change in characteristics when the temperature of the fluid changes, and the temperature characteristics are improved.

(Embodiment 8)
In the seventh embodiment, the fluid temperature detection resistor 55 (Ra) is connected in series with the resistors R1 and R2 so that the voltage 19 (Vt) varies depending on the fluid temperature. However, as understood from Equation 12 , the same effect can be obtained even when the voltage Ve is changed depending on the fluid temperature. For example, a configuration as shown in FIG. 17 may be employed.

FIG. 17 is a circuit diagram for outputting voltage Ve in the eighth embodiment. In this circuit, a voltage obtained by dividing the constant voltage source 56 by the fixed resistors (R3, R4) and the fluid temperature detecting resistor 55 is output as the voltage Ve. Since the change in the fluid temperature is detected using the fluid temperature detection resistor 55, Ve can be changed when the fluid temperature changes. Therefore, it is possible to average value of the temperature (Tsd) temperature (Tsu) and downstream temperature sensing resistor 6 (FIG. 16) of the upstream side temperature sensing resistor 5 (FIG. 16) is also varied by the fluid temperature Ta. Fluid temperature Ta and the upstream side temperature sensing resistor 5, the relationship between the average temperature of the downstream temperature sensing resistor 6 may be adjusted by the fixed resistor R3 and R4 in FIG. 17.

  According to the above configuration, the change in characteristics when the temperature of the fluid changes can be compensated, and the temperature characteristics are improved.

(Embodiment 9)
As described in the eighth embodiment, if a fluid temperature detection resistor is used, a change in characteristics reflecting a change in fluid temperature can be guaranteed.

FIG. 18 is a circuit diagram of a fluid flow rate measurement device in which the fluid temperature detection resistor 55 is inserted in the ninth embodiment.

FIG. 3 is a diagram illustrating a configuration of a measurement unit of the fluid flow measurement device according to the first embodiment. 1 is a circuit diagram of a fluid flow rate measuring device including six resistors according to Embodiment 1. FIG. It is a figure which shows the relationship between the terminal voltage of the resistors 68-71 (FIG. 2 ), and the voltage of the output terminals 16 and 81 (FIG. 2 ). It is a figure which shows the relationship between Vout1, Vout2 and Vh1-Vh4. It is a figure which shows the process for outputting a final output. It is a graph of the final output voltage 97 obtained from the two output voltages 94 and 95. It is a figure which shows the process for outputting the output voltage 86 (Vout1) and 87 (Vout2) demonstrated in FIG. 5 digitally. It is a figure which shows the process for outputting a duty ratio difference. It is a figure which shows another process for outputting the output voltage 86 (Vout1) and 87 (Vout2) demonstrated in FIG. 5 digitally. FIG. 10 is a diagram illustrating a configuration of a measurement unit of a fluid flow measurement device according to a fifth embodiment. FIG. 10 is a circuit diagram of a fluid flow rate measuring device including resistors 4, 5, and 6 in a fifth embodiment. It is a graph of the temperature change of the upstream temperature detection resistor 5 and the downstream temperature detection resistor 6 according to the flow volume of the fluid. It is a graph which shows the flow rate dependence of the difference of the temperature of the upstream temperature detection resistor 5 and the temperature of the downstream temperature detection resistor 6. FIG. 10 is a diagram illustrating a configuration of a measurement unit of a fluid flow measurement device according to a sixth embodiment. FIG. 10 is a diagram illustrating a configuration of a measurement unit of a fluid flow measurement device according to a seventh embodiment. FIG. 10 is a circuit diagram of a fluid flow rate measurement device including a fluid temperature detection resistor 55 according to a seventh embodiment. FIG. 20 is a circuit diagram for outputting a voltage Ve in the eighth embodiment. FIG. 20 is a circuit diagram of a fluid flow rate measuring device with a fluid temperature detection resistor 55 inserted in a ninth embodiment.

  DESCRIPTION OF SYMBOLS 1 Silicon substrate, 3 Thin part, 4 Heating resistor, 5 Upstream temperature detection resistor, 6 Downstream temperature detection resistor, 7 Insulating layer, 8 Insulating layer, 9 Wiring part, 10 Pad part, 13 Constant current source, 68 first heat generating resistor, 69 second heat generating resistor, 70 third heat generating resistor, 71 fourth heat generating resistor, 72 differential amplifier.

Claims (3)

In the flow rate measuring device that measures the flow rate of the fluid from the difference between the heat release amount on the upstream side and the heat release amount on the downstream side of the heating element that is arranged in the fluid and generates heat,
1st, 2nd, 3rd, 4th, 5th, 6th sense which is arrange | positioned from the upstream of the fluid to the downstream, and each has the function of the heat generating body which generates heat, and the temperature detection body which detects temperature. A thermal resistor,
A control circuit for controlling supply of electric power for generating heat in the temperature sensitive resistor;
The first, second, fifth, and sixth temperature sensitive resistors are connected to a constant current source or a constant voltage source, and the second, third, fourth, and fifth temperature sensitive resistors are Connected to the power supply,
The control circuit includes a first comparison circuit that compares the temperatures of the first and sixth temperature sensitive resistors, a second comparison circuit that compares the temperatures of the second and fifth temperature sensitive resistors, A plurality of switches arranged between a power source and the second, third, fourth, and fifth temperature sensitive resistors, the temperature comparison result by the first comparison circuit and the temperature comparison by the second comparison circuit Based on the result, an opening / closing operation is performed to supply power from the power source to one of the first, second, third, and fourth temperature sensitive resistors, and the first The second and fifth temperature sensitive resistors have the same temperature , and the switch has the same that the first and sixth temperature sensitive resistors have the same temperature. 4 based on the difference between the power supplied to the temperature sensitive resistor 4 and the difference between the power supplied to the second and fifth temperature sensitive resistors. Flow rate measuring device for measuring the flow rate. Furthermore, a heating resistor is provided between the third and fourth temperature sensitive resistors,
The control circuit controls electric power supplied to the heating resistor so that an average temperature of the first temperature sensing resistor and the sixth temperature sensing resistor becomes a preset temperature. The flow measurement device described in 1. The flow measurement device according to claim 2, wherein the control circuit changes the preset temperature based on a temperature of the fluid.

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