JP3819185B2 - Flow velocity measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thermal type flow velocity measuring apparatus that is used in a gas flow meter, a flow meter, and the like and measures a flow velocity by a temperature change of resistance caused by a fluid.
[0002]
[Prior art]
Such a flow velocity measuring device is disclosed in, for example, Japanese Patent Laid-Open No. 10-206205.
[0003]
[Problems to be solved by the invention]
FIG. 3 shows one configuration example of the flow rate measuring device. This flow rate measuring device is roughly constituted by a sensor driving unit 1, a differential voltage detection unit 2, and an amplification unit 3. In the sensor driving unit 1, a first temperature sensitive resistor RS1 and a second temperature sensitive resistor RS2 mounted on a sensor substrate (not shown) disposed in the flow path are provided. Yes. These first and second temperature sensitive resistors RS1 and RS2 are also exposed to the fluid. Here, the first temperature sensitive resistor RS1 is upstream, and the second temperature sensitive resistor RS2 is downstream. It is assumed that the positional relationship is set so that The first and second temperature sensitive resistors RS1 and RS2 have the same resistance value and a high resistance temperature coefficient. These first and second temperature sensitive resistors RS1 and RS2 are connected in series with a current source 4 that acts as a heating device. That is, the current source 4 flows the current I1 to generate Joule heat in the resistor itself, so that the first and second temperature-sensitive resistors RS1 and RS2 are equally heated so that the temperature becomes higher than the fluid temperature. (However, as a heating device, the first and second temperature sensitive resistors RS1 and RS2 may be heated by separate heat sources). In the sensor driving unit 1, the operational amplifier 5 in which both ends b and c of the second temperature sensing resistor RS2 are connected in the feedback loop, and the connection point between the current source 4 and the first temperature sensing resistor RS1. An operational amplifier 6 connected to the output side of a is provided.
[0004]
The differential voltage detection unit 2 functions as a detection device. The terminal voltage of the first temperature sensing resistor RS1 output from the operational amplifier 6 to the point d (= output at the point f) and the operational amplifier 5 from the point c (= e An adder 7 is provided for outputting a voltage difference from the terminal voltage of the second temperature-sensitive resistor RS2 (= output at the point h) to the point g.
[0005]
The amplifying unit 3 includes amplifiers 8, 9, and 10 that amplify the terminal voltage of the first temperature sensitive resistor RS1, the terminal voltage of the second temperature sensitive resistor RS2, and the differential voltage (g point output), respectively. ing.
[0006]
In such a configuration, the heat of the first and second temperature sensitive resistors RS1, RS2 is taken away by the flow of fluid. The amount of heat taken away is related to the fluid flow. For example, if there is no flow of fluid, the temperatures of the first and second temperature sensitive resistors RS1, RS2 are substantially equal, so the resistance values are also approximately equal. Therefore, the terminal voltage of the first temperature sensitive resistor RS1 and the terminal voltage of the second temperature sensitive resistor RS2 are substantially equal, and the output at the point g of the differential voltage detector 2 is also substantially zero. On the other hand, when the fluid is flowing, the heat of the first temperature-sensitive resistor RS1 on the upstream side is deprived more than that on the downstream side, so the temperatures of the first and second temperature-sensitive resistors RS1 and RS2 are different. That is, the resistance value of the first temperature-sensitive resistor RS1 on the upstream side is smaller than that on the downstream side. Therefore, the terminal voltage of the first temperature sensitive resistor RS1 is smaller than the terminal voltage of the second temperature sensitive resistor RS2. This terminal voltage difference appears as a voltage value related to the flow velocity. As a result, it can be said that the flow velocity of the fluid can be known by measuring the magnitude of the output at the point g of the differential voltage detector 2. Note that when an A / D converter or the like is used to measure these terminal voltages, differential voltages, etc., it is necessary to convert the voltage signal to match the A / D converter, etc., and therefore an amplifying unit 3 is provided in the subsequent stage. ing.
[0007]
However, the apparatus shown in FIG. 3 uses a plurality of operational amplifiers, and thus consumes a large amount of power and cannot be driven with a battery for a long time.
[0008]
An object of the present invention is to provide a flow rate measuring device suitable for driving with a battery power source by suppressing power consumption.
[0009]
Another object of the present invention is to make it possible to obtain more accurate temperature compensation information of the fluid flow velocity.
[0010]
Another object of the present invention is to enable continuous flow rate information to be output.
[0011]
Another object of the present invention is to enable timely output of fluid temperature information.
[0012]
[Means for Solving the Problems]
The invention according to claim 1 is a flow velocity measuring apparatus for measuring a flow velocity of the fluid from a terminal voltage difference between two temperature-sensitive resistors that are respectively arranged on the upstream side and the downstream side in the fluid to heat. Two voltage holding devices that follow the terminal voltage of the temperature resistor and hold the voltage, an amplifier, and the voltage holding device so that one terminal voltage of the temperature sensitive resistor can be amplified by the amplifier. A flow rate measuring device comprising: a first switch capable of switching a connection state of lines so that a difference between voltages held therein can be amplified by the amplifier.
[0013]
Therefore, if the voltage held by both voltage holding devices is set to a common potential, for example, a voltage based on GND, and the difference between the voltages held by both voltage holding devices is amplified by an amplifier, the flow rate of the fluid can be increased. Can be measured. Since this device has a circuit configuration that uses only a single amplifier, it can save power and is suitable for driving with a battery power source. Further, the temperature of the fluid can be detected by amplifying the voltage held on one side of the voltage holding device by an amplifier, and information on temperature compensation of the flow velocity of the fluid can be obtained.
[0014]
According to a second aspect of the present invention, there is provided a flow velocity measuring apparatus for measuring a flow velocity of the fluid from a terminal voltage difference between two temperature-sensitive resistors that are respectively arranged on the upstream side and the downstream side in the fluid to heat the fluid. Two voltage holding devices that hold the voltage following the terminal voltage of the temperature resistor, an amplifier, a temperature measuring resistor that measures the temperature of the fluid, and a voltage across the terminals of the temperature measuring resistor And a first switch that can switch the line connection state so that the amplifier can amplify the difference between the voltages held by the two voltage holding devices. Is a flow velocity measuring device.
[0015]
Therefore, if the voltage held by both voltage holding devices is set to a common potential, for example, a voltage based on GND, and the difference between the voltages held by both voltage holding devices is amplified by an amplifier, the flow rate of the fluid can be increased. Can be measured. Since this device has a circuit configuration that uses only a single amplifier, it can save power and is suitable for driving with a battery power source. Further, the temperature of the fluid can be detected by amplifying the voltage between the terminals of the resistance temperature detector using an amplifier, and the temperature compensation information of the fluid flow velocity can be obtained more accurately.
[0016]
A third aspect of the present invention is the flow rate measuring device according to the first or second aspect, further comprising a second switch for opening and closing a line for supplying power to the circuit of the present apparatus.
[0017]
Therefore, when there is no need to measure the flow velocity, the power supply to the circuit can be stopped, so that driving with a battery power source becomes easy.
[0018]
According to a fourth aspect of the present invention, in the flow rate measuring device according to any one of the first to third aspects, the amplifier can vary an amplification factor.
[0019]
Therefore, it is possible to amplify the voltage difference between the two temperature sensitive resistors and amplify the terminal voltage of the temperature sensitive resistor or the terminal voltage of the temperature sensing resistor with the same amplifier, and measure the flow velocity without increasing the number of amplifiers. Temperature measurement and power consumption can be reduced.
[0020]
According to a fifth aspect of the present invention, in the flow velocity measuring device according to any one of the first to fourth aspects, the voltage holding device can hold the voltage following the terminal voltage of each of the temperature sensitive resistors. And a third switch capable of switching the line connection state so that the voltage held in the voltage holding device can be applied to the amplifier.
[0021]
Therefore, the measurement of the terminal voltage of each temperature sensitive resistor and the measurement of the flow velocity of the fluid can be alternately repeated, and continuous flow velocity information can be output.
[0022]
A sixth aspect of the present invention is the flow velocity measuring apparatus according to any one of the first to fifth aspects, further comprising a current source that supplies current to the temperature sensitive resistor, and the current source stops the current. Alternatively, it can be reduced.
[0023]
Therefore, power consumption when there is no need for flow velocity measurement is suppressed, and driving with a battery power source becomes easy.
[0024]
According to a seventh aspect of the present invention, in the flow velocity measuring device according to the sixth aspect, the difference between the voltages held by the two voltage holding devices can be amplified by the amplifier by switching the first switch. The current source is provided with current control means for stopping or reducing the current supplied to the temperature sensitive resistor.
[0025]
Therefore, power consumption when the flow velocity measurement is not performed is suppressed, and driving with the battery power source becomes easy.
[0026]
The invention according to claim 8 is the flow velocity measuring device according to any one of claims 1 to 7, wherein the first switch is switched at an appropriate time so that one terminal voltage of the thermosensitive resistor or the temperature measurement is performed. A temperature measuring means is provided for enabling the terminal voltage of the resistor to be amplified by the amplifier.
[0027]
Therefore, it is possible to output fluid temperature information in a timely manner.
[0028]
The ninth aspect of the present invention is the flow velocity measuring apparatus according to the third aspect, wherein the voltage holding device is made to follow the terminal voltage of each of the temperature sensitive resistors to hold the voltage. ,as well as, Operation of amplifying one terminal voltage of the temperature sensitive resistor or the terminal voltage of the temperature measuring resistor by switching the first switch by the amplifier And Operation of amplifying the difference between the voltages held by the two voltage holding devices by the amplifier When the continuous flow velocity measurement is performed by appropriately switching the Switch the second switch to open a line to supply power to the circuit of the device The power to the circuit is cut off, the voltage holding device is made to follow the terminal voltage of each of the temperature sensitive resistors to hold the voltage, and one terminal voltage of the temperature sensitive resistor or The operation of amplifying the terminal voltage of the resistance temperature detector by the amplifier and the operation of amplifying the difference between the voltages held by the two voltage holding devices by the amplifier are suspended. .
[0029]
Therefore, intermittent flow velocity measurement can be performed, power consumption during a period when flow velocity measurement is not necessary is suppressed, and driving with a battery power source is facilitated.
[0030]
The invention according to claim 10 is the flow velocity measuring device according to claim 1 or 2, wherein the voltage holding device is made to follow the terminal voltage of each of the temperature sensitive resistors and hold the voltage, It is characterized by comprising simultaneous execution means for switching the first switch and simultaneously amplifying the one terminal voltage of the temperature sensitive resistor or the terminal voltage of the temperature measuring resistor by the amplifier.
[0031]
Accordingly, the measurement of the flow velocity and the measurement of the fluid temperature are performed at the same time, the time required for these is reduced, the power consumption is suppressed, and the driving with the battery power source becomes easy.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 of the Invention
1 is a circuit diagram of a flow velocity measuring apparatus according to Embodiment 1 of the present invention. As shown in FIG. 1, the flow velocity measuring device includes temperature sensitive resistors Ru and Rd. The temperature sensitive resistors Ru and Rd are installed in the fluid, the temperature sensitive resistor Ru is installed on the upstream side, and the temperature sensitive resistor Rd is installed on the downstream side. The temperature sensitive resistors Ru and Rd have a high temperature coefficient of resistance such as platinum, the resistance value and the temperature coefficient of resistance are equal, the shape is the same, and the thermal characteristics such as heat dissipation are the same, Both generate heat by electric power.
[0033]
The current source Ih supplies current to the temperature sensitive resistors Ru and Rd connected in series. The current source Ih is connected to one end of the temperature sensitive resistor Rd at node A. The other end of the temperature sensitive resistor Rd is connected to one end of the temperature sensitive resistor Ru at node B. The other end of the temperature sensitive resistor Ru is grounded.
[0034]
Reference numerals C1 and C2 denote capacitors which are voltage holding devices. Symbol U1 is a differential amplifier which is an amplifier. Reference numerals SW1, SW2, SW3, SW4, SW5, and SW6 are switches, such as semiconductor switches that can be opened and closed by electric signals. The switches SW5 and SW6 constitute a first switch. The switches SW1, SW2, SW3 and SW4 constitute a third switch.
[0035]
The control signal S1 is a signal that controls opening and closing of the switches SW1, SW2, SW3, and SW4. The control signal S2 is a signal that controls opening and closing of the switches SW5 and SW6. The switch SW3 is a signal for switching the amplification factor of the differential amplifier U1. The control signal S4 is a signal for controlling the current value of the current source Ih. The control signal S5 is a signal for opening and closing a line for supplying power to the circuit of FIG. The control signals S1, S2, S3, S4 and S5 are output from a microcomputer (not shown) that drives the flow velocity measuring device.
[0036]
The control signal S1 is a signal for switching between two types of states, a tracking state and a holding state. In the follow-up state, the switch SW1 connects the node D of one end of the capacitor C1 and the node A of one end of the temperature sensitive resistor Rd, and the switch SW2 connects the node E of the other end of the capacitor C1 and the other end of the temperature sensitive resistor Rd. Connect Section B. The switch SW3 connects the F node at one end of the capacitor C2 and the B node at one end of the temperature sensitive resistor Ru, and the switch SW4 connects the G node at the other end of the capacitor C2 and the C node at the other end of the temperature sensitive resistor Ru. Connect. In the holding state, the switch SW1 connects the D and H nodes at one end of the capacitor C1, and the switch SW2 connects the E and I nodes at the other end of the capacitor C1. The switch SW3 connects the F node and the J node at one end of the capacitor C2, and the switch SW4 connects the G node and the I node at the other end of the capacitor C2.
The control signal S2 is a signal for switching between two types of states, a temperature measurement state and a flow velocity measurement state. In the temperature measurement state, the switch SW5 connects the node A at one end of the temperature sensing resistor Rd and the non-inverting input terminal of the differential amplifier U1, and the switch SW6 is differential with the node B at the other end of the temperature sensing resistor Rd. The inverting input terminal of the amplifier U1 is connected. In the flow velocity measurement state, the switch SW5 connects the H node and the non-inverting input terminal of the differential amplifier U1, and the switch SW6 connects the J node and the inverting input terminal of the differential amplifier U1.
[0037]
The control signal S4 is a signal for switching between the heat generation state and the standby state. In the heat generation state, the current source Ih supplies a current that causes the temperature sensitive resistors Ru and Rd to generate heat. In the standby state, the current source Ih stops the current source Ih or reduces the current value so that the temperature sensitive resistors Ru and Rd do not generate heat.
[0038]
The control signal S3 is a signal for switching between the energized voltage state and the minute voltage state. In the normal voltage state, the amplification factor of the differential amplifier U1 is made small, for example, 1 time. In the minute voltage state, the amplification factor of the differential amplifier U1 is increased, for example, 40 times.
[0039]
The control signal S5 is a signal for turning on / off the power to the circuit of FIG. In the ON state, a switch (not shown) which is a second switch for opening and closing a line for supplying power to the circuit of FIG. 1 is closed. In the OFF state, the switch for opening and closing the line for supplying power to the circuit of FIG. 1 is opened to cut off the power.
[0040]
Next, the operation of the flow velocity measuring apparatus configured as described above will be described. When the circuit of FIG. 1 is in the OFF state by the control signal S5, the circuit does not operate because the power is cut off. This is hereinafter referred to as a rest period. During this idle period, the supply of power from the power source to the circuit of FIG. 1 is minimal.
[0041]
Next, the control signal S5 is set to the ON state, the control signal S1 is set to the follow-up state, the control signal S4 is set to the heat generation state, and the control signals S2 and S3 are set to arbitrary states. This is hereinafter referred to as a flow velocity measurement period. The electric power is supplied, and the circuit of FIG. 1 becomes operable, and the current source Ih supplies the current to the temperature-sensitive resistor elements Ru and Rd. The temperature sensitive resistors Ru and Rd generate heat due to the current supplied from the current source Ih. Terminal voltages generated in the temperature sensitive resistors Ru and Rd pass through the switches SW1, SW2, SW3 and SW4 and are stored in the capacitors C1 and C2, respectively. As a result, the terminal voltage of the temperature sensitive resistor Ru and the terminal voltage of the capacitor C1, and the terminal voltage of the temperature sensitive resistor Rd and the terminal voltage of the capacitor C2 are equal.
[0042]
After a sufficient time has elapsed for the temperature sensitive resistors Ru and Rd to generate heat, the control signal S1 is held, the control signal S2 is set to the flow velocity measurement state, and the control signal S3 is set to a minute voltage state. This is hereinafter referred to as a flow velocity output period. Since the input impedance of the differential amplifier U1 is high, the terminal voltages of the temperature sensitive resistors Rd and Ru are held in the capacitors C1 and C2, respectively. Since the E node side of the capacitor C1 and the G node side of the capacitor C2 are grounded via the switches SW2 and SW4, the voltage value of the temperature sensitive resistor Rd with respect to the ground point appears in the H node, and the J node The voltage value of the temperature sensitive resistor Ru with respect to the ground point appears. Since the switch SW2 is in the flow velocity measurement state, the terminal voltage of Rd is input to the non-inverting input terminal of the differential amplifier U1, and the terminal voltage of Ru is input to the inverting input terminal. Therefore, the voltage difference between the H node and the J node, that is, the value obtained by subtracting the terminal voltage of the temperature sensing resistor Ru from the terminal voltage of the temperature sensing resistor Rd is amplified and output at the node O on the output side of the differential amplifier U1. Is done.
[0043]
Further, when the control signal S5 is in the ON state and the control signal S4 is in the heat generation state, when the control signal S2 is in the temperature measurement state and the control signal S3 is in the normal voltage state, the output of the differential amplifier U1 has a temperature sensitive resistor. The terminal voltage of Rd is output. Thereby, a temperature measuring means is realized. This is hereinafter referred to as a temperature output period.
[0044]
During the flow velocity measurement period, the temperature sensitive resistors Ru and Rd generate heat due to the current from the current source Ih, and the flow velocity is measured. Since the temperature sensitive resistors Ru and Rd have the same characteristics, the resistance values are equal. When there is no flow in the fluid, the same current flows through the temperature-sensitive resistors Ru and Rd even when the fluid is in a heated state. That is, the terminal voltages of the temperature sensitive resistors Ru and Rd are equal. This voltage is stored in capacitors C1 and C2, respectively.
Next, it shifts to the flow velocity output period. Since the terminal voltages of the capacitors C1 and C2 are equal, the voltage values of the non-inverting input terminal and the inverting input terminal of the differential amplifier U1 are equal. That is, the differential voltage 0 is input to the differential amplifier U1. Therefore, the output of the differential amplifier U1 becomes zero.
[0045]
When the fluid is flowing, the heat generated by the temperature sensitive resistors Ru and Rd is removed by the fluid during the flow velocity measurement period. However, since the temperature sensitive resistor Rd is installed on the downstream side of the temperature sensitive resistor Ru, the heat deprived from the temperature sensitive resistor Ru is carried to the temperature sensitive resistor Rd. Therefore, the temperature sensitive resistor Rd is less deprived of heat than the temperature sensitive resistor Ru. When heat is taken away, the resistance values of the temperature sensitive resistors Ru and Rd decrease. The decrease in the resistance value of the temperature sensitive resistor Rd is smaller than the decrease in the resistance value of the temperature sensitive resistor Ru. That is, the terminal voltage value of the temperature sensitive resistor Ru is smaller than the terminal voltage value of the temperature sensitive resistor Rd. This voltage difference is related to the flow velocity of the fluid, and increases as the flow velocity increases. This voltage is stored in capacitors C1 and C2.
Next, it shifts to the flow velocity output period. The voltage of the capacitor C1 is applied to the non-inverting input terminal of the differential amplifier U1, and the voltage of C2 is applied to the inverting input terminal of the differential amplifier U1. The difference between the voltages of the capacitors C1 and C2 is amplified by the differential amplifier U1 and appears at the output. That is, an output related to the flow velocity is obtained.
[0046]
When the fluid is flowing backward, the heat sensitive resistor Ru loses less heat than the temperature sensitive resistor Rd. It may be considered that the relationship between the temperature sensitive resistors Ru and Rd is reversed up and down. That is, it appears in the output of the flow velocity output period with the opposite sign to that in the normal flow. Therefore, it is possible to determine the normal flow and the reverse flow of the fluid by the sign of the output signal during the flow velocity output period. And a continuous flow velocity measurement can be performed by repeating a flow velocity measurement period and a flow velocity output period alternately.
[0047]
In the temperature measurement period, the terminal voltage of the temperature sensitive resistor Rd is given to the differential input of the differential amplifier U1. Therefore, the terminal voltage of the temperature sensitive resistor Rd is amplified and output. The temperature sensitive resistor Rd changes its resistance value depending on the temperature of the fluid. That is, the terminal voltage of the temperature sensitive resistor Rd is a value related to the temperature of the fluid. The temperature of the fluid can be known from the output of the differential amplifier U1 during the temperature measurement period. This value makes it possible to correct the temperature dependence in the flow velocity measurement.
[0048]
As described above, continuous flow velocity measurement can be performed by switching the flow velocity measurement period, the flow velocity output period, and the temperature measurement period in a timely manner.
[0049]
Further, the control signal S5 is set to the ON state, the control signal S1 is set to the follow-up state, the control signal S4 is set to the heat generation state, the control signal S2 is set to the temperature measurement state, and the control signal S3 is set to the normal voltage state. Then, current is supplied to the temperature sensitive resistors Ru and Rd to generate heat, and the terminal voltage is transmitted to the capacitors C1 and C2. At the same time, the terminal voltage of the temperature sensitive resistor Rd is supplied to the differential input terminal of the differential amplifier U1. The amplified terminal voltage of the temperature sensitive resistor Rd is output to the node O. That is, the flow rate measurement period and the temperature measurement period are performed simultaneously. This realizes simultaneous execution means. Since the temperature measurement can be performed during the flow velocity measurement period, the time required for the temperature measurement period can be omitted, and the flow velocity measurement and the fluid temperature measurement can be performed in a short time, thereby reducing power consumption. When there is no need to measure the flow velocity, the power consumption can be suppressed by setting the suspension period. Thereby, a pause means is realized. In the flow velocity output period, the current source Ih is stopped or the current value is reduced by the control signal S4. This implements a current control means.
[0050]
Here, for example, if the temperature sensitive resistors Ru and Rd are formed by a microbridge sensor formed on a silicon substrate as disclosed in Japanese Patent Application Laid-Open No. 10-206205, the microbridge sensor has a minute structure, and therefore requires less power. Since heat is generated before the flow rate can be measured, a low-power flow rate sensor is obtained.
[0051]
The temperature sensitive resistors Ru and Rd by the micro bridge are set to about 500Ω at room temperature, for example. For example, when 1.75 mA is passed as the current source Ih, the temperature sensitive resistors Ru and Rd generate heat at about 100 ° C. At this time, the terminal voltage of the temperature sensitive resistors Ru and Rd is about 1.2V. When flow occurs in the fluid, there is a slight difference between the terminal voltages of the temperature sensitive resistors Ru and Rd. The difference is about 60 mV at maximum. If the flow of the flow velocity is too fast, there will be no difference in the heat deprived of the temperature sensitive resistors Ru and Rd. Therefore, the difference in terminal voltage between the temperature sensitive resistors Ru and Rd due to the flow velocity increases as the flow velocity increases. Saturating gradually, and the difference disappears. For the flow velocity measurement, a portion where the terminal voltage difference increases in relation to the flow velocity is used.
When this apparatus is driven by a battery or the like, it is desirable that the output has a value of about 0 to 3V. Since the terminal voltage of about 1.2 V of the temperature sensitive resistor Rd is amplified and output during the temperature measurement period, the amplification factor of the differential amplifier U1 may be increased to 1 to 2 times. In the flow rate output period, about 60 mV of the voltage difference between the temperature sensitive resistors Ru and Rd is amplified, so the amplification factor of the differential amplifier U1 may be about 50 times. When it is desired to measure the reverse flow with a single power source, the offset of the output of the differential amplifier U1 can be shifted in the positive voltage direction.
[0052]
[Embodiment 2 of the Invention]
FIG. 2 is a circuit diagram of a flow velocity measuring apparatus according to the second embodiment of the present invention. In FIG. 2, the same reference numerals as those in FIG. 1 are assigned to circuit elements and the like similar to those in the first embodiment of the invention, and detailed description thereof will be omitted.
[0053]
In Embodiment 1 of the invention, the terminal voltage of the temperature-sensitive resistor Rd is output during the temperature measurement period, and is used as a fluid temperature signal. In the second embodiment of the present invention, since the temperature sensing resistor Rd is affected by the flow velocity and changes its voltage, the temperature sensing resistor Rf for measuring the temperature of the fluid is used as the temperature sensing resistor for more accurate temperature measurement. This is an example provided separately from the bodies Ru and Rd.
[0054]
The resistance temperature detector Rf is a resistor having a large resistance temperature coefficient, such as platinum. The resistance temperature detector Rf is installed at a position not affected by the heat generated by the temperature sensitive resistors Ru and Rd in the fluid. The resistance temperature detector Rf is connected to the current source If.
[0055]
In the temperature measurement state according to the first embodiment of the present invention, the switches SW5 and SW6 are switched so as to differentially input the terminal voltage of the temperature sensitive resistor Rd to the differential amplifier U1. In the second embodiment, the terminal voltage of the resistance temperature detector Rf is differentially input to the differential amplifier U1. As a result, the temperature of the fluid can be measured without being affected by the flow velocity, and information for more accurate temperature correction can be obtained.
[0056]
If the resistance temperature detector Rf is also formed as a platinum thin film on a silicon substrate as disclosed in JP-A-10-206205, the heat capacity is small and the temperature of the fluid can be obtained accurately. The resistance value of the resistance temperature detector Rf is, for example, about 5 kΩ at room temperature, and a current of about 100 μA is supplied from the current source If. Then, the terminal voltage of the resistance temperature detector Rf becomes about 0.5V. This voltage varies with the temperature of the fluid. At this time, the amplification factor of the differential amplifier U1 during the temperature measurement period may be about 1 to 3 times.
[0057]
Note that the resistance values and amplification factors shown in the embodiments of the present invention are only examples, and other values may of course be used. These are designed according to the available power supply voltage, the temperature sensitive resistor, the characteristics of the resistance temperature detector, and the characteristics of the fluid to be measured.
[0058]
【The invention's effect】
According to the first aspect of the present invention, the voltage held by both voltage holding devices is set to a common potential, for example, a voltage based on GND, and the difference between the voltages held by both voltage holding devices is amplified by an amplifier. Then, the flow rate of the fluid can be measured. Since this device has a circuit configuration that uses only a single amplifier, it can save power and is suitable for driving with a battery power source. Further, the temperature of the fluid can be detected by amplifying the voltage held on one side of the voltage holding device by an amplifier, and information on temperature compensation of the flow velocity of the fluid can be obtained.
[0059]
According to the second aspect of the present invention, the voltage held by both voltage holding devices is set to a common potential, for example, a voltage based on GND, and the difference between the voltages held by both voltage holding devices is amplified by an amplifier. Then, the flow rate of the fluid can be measured. Since this device has a circuit configuration that uses only a single amplifier, it can save power and is suitable for driving with a battery power source. Further, the temperature of the fluid can be detected by amplifying the voltage between the terminals of the resistance temperature detector using an amplifier, and the temperature compensation information of the fluid flow velocity can be obtained more accurately.
[0060]
According to the third aspect of the present invention, in the flow rate measuring device according to the first or second aspect, when the flow velocity measurement is not required, the power supply to the circuit can be stopped. Become.
[0061]
According to a fourth aspect of the present invention, in the flow rate measuring apparatus according to any one of the first to third aspects, the voltage difference between the two temperature sensitive resistors is amplified and the terminal voltage of the temperature sensitive resistor is amplified or measured. The terminal voltage of the resistor can be amplified by the same amplifier, and the flow velocity and temperature can be measured without increasing the number of amplifiers, and the power consumption can be suppressed.
[0062]
According to a fifth aspect of the present invention, in the flow velocity measuring device according to any one of the first to fourth aspects, the measurement of the terminal voltage of each temperature sensitive resistor and the measurement of the flow velocity of the fluid are repeated alternately. It is possible to output continuous flow rate information.
[0063]
According to a sixth aspect of the present invention, in the flow velocity measuring device according to any one of the first to fifth aspects, the power consumption when there is no need for the flow velocity measurement is suppressed, and the driving with the battery power source becomes easy. .
[0064]
According to a seventh aspect of the present invention, in the flow velocity measuring device according to the sixth aspect, power consumption when the flow velocity measurement is not performed is suppressed, and driving with a battery power source becomes easy.
[0065]
According to an eighth aspect of the present invention, in the flow velocity measuring device according to any one of the first to seventh aspects, fluid temperature information can be output in a timely manner.
[0066]
According to a ninth aspect of the present invention, in the flow velocity measuring device according to the third aspect, intermittent flow velocity measurement can be performed, and power consumption during a period when the flow velocity measurement is not necessary is suppressed, and driving with a battery power source is performed. Becomes easy.
[0067]
According to a tenth aspect of the present invention, there is provided the flow velocity measuring device according to the first or second aspect, wherein the flow velocity measurement and the fluid temperature measurement are simultaneously performed, the time required for these is shortened, and the power consumption is reduced, thereby reducing the battery. Driving with a power supply becomes easy.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a flow velocity measuring device according to a first embodiment of the present invention.
FIG. 2 is a circuit diagram of a flow velocity measuring apparatus according to a second embodiment of the present invention.
FIG. 3 is a circuit diagram of a conventional flow velocity measuring device.
[Explanation of symbols]
Ru, Rd Temperature sensitive resistor
Ih current source
C1, C2 voltage holding device
U1 amplifier
SW1 to SW4 Third switch
SW5, SW6 first switch
Rf RTD

Claims (10)

In the flow velocity measuring device that measures the flow velocity of the fluid from the terminal voltage difference between two temperature sensitive resistors that are respectively arranged on the upstream side and the downstream side in the fluid to heat,
Two voltage holding devices that hold the voltage following the terminal voltage of each of the temperature sensitive resistors;
An amplifier;
The connection state of the lines can be switched so that one terminal voltage of the temperature sensitive resistor can be amplified by the amplifier and the difference between the voltages held by the two voltage holding devices can be amplified by the amplifier. A flow velocity measuring device comprising: a first switch. In the flow velocity measuring device that measures the flow velocity of the fluid from the terminal voltage difference between two temperature sensitive resistors that are respectively arranged on the upstream side and the downstream side in the fluid to heat,
Two voltage holding devices that hold the voltage following the terminal voltage of each of the temperature sensitive resistors;
An amplifier;
A resistance thermometer for measuring the temperature of the fluid;
The line connection state can be switched so that the terminal voltage of the resistance temperature detector can be amplified by the amplifier and the difference between the voltages held by the two voltage holding devices can be amplified by the amplifier. 1 is a flow velocity measuring device. The flow rate measuring device according to claim 1, further comprising a second switch for opening and closing a line for supplying power to the circuit of the device. The flow rate measuring apparatus according to claim 1, wherein the amplifier has a variable amplification factor. The connection state of the line can be switched so that the voltage holding device can hold the voltage following the terminal voltage of each temperature-sensitive resistor and also can apply the voltage held in the voltage holding device to the amplifier. The flow velocity measuring device according to claim 1, further comprising: a third switch that is The flow velocity measuring device according to claim 1, further comprising a current source that supplies current to the temperature-sensitive resistor, and the current source can stop or reduce the current. When the difference between the voltages held by the two voltage holding devices can be amplified by the amplifier by switching the first switch, the current supplied from the current source to the temperature sensitive resistor is stopped. The flow velocity measuring device according to claim 6, further comprising a current control means for reducing the current. A temperature measuring means is provided for switching the first switch in a timely manner so that one terminal voltage of the temperature sensitive resistor or the terminal voltage of the temperature measuring resistor can be amplified by the amplifier. Item 8. The flow velocity measuring device according to any one of Items 1 to 7. The operation of causing both voltage holding devices to follow the terminal voltage of each of the temperature sensitive resistors and holding the voltage , and one terminal voltage of the temperature sensitive resistor or the temperature measurement by switching the first switch. operation for amplifying the terminal voltage of the resistor by said amplifier, and configured to perform the flow rate measurement both voltage holding device is continuous by switching the difference in voltages held respectively appropriate action amplified by the amplifier When there is no need to measure the flow velocity , the power to the circuit is cut off by switching the second switch and opening a line for supplying power to the circuit of the apparatus. The operation of keeping the voltage by following the terminal voltage of each of the temperature sensitive resistors, and one terminal voltage of the temperature sensitive resistor or the terminal voltage of the temperature measuring resistor by the amplifier. Operation of amplifying as well as the flow rate measuring apparatus according to the difference between the voltage the both voltages holding device holds each to claim 3, characterized in that halting the operation of amplifying by the amplifier. The operation of causing both voltage holding devices to follow the terminal voltage of each of the temperature sensitive resistors and holding the voltage, and switching the first switch to one terminal voltage of the temperature sensitive resistor or the temperature measuring resistor. The flow velocity measuring device according to claim 1, further comprising a simultaneous execution unit that simultaneously performs an operation of amplifying a body terminal voltage by the amplifier.

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