JP2001074761A - Flow velocity measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flow velocity measuring device that is suitable for driving with a battery power supply by suppressing power consumption. SOLUTION: In the flow velocity measuring device, thermally sensitive resistors Rd and Ru are arranged at upstream and downstream sides in fluid, respectively. Capacitors C1 and C2 follow the terminal voltage of the thermally sensitive resistors Rd and Ru for maintaining the voltage. Switches SW5 and SW6 are changed, thus amplifying one terminal voltage of the thermally sensitive resistors Rd and Ru by a differential amplifier U1, and at the same time allowing voltage difference being maintained by the capacitors C1 and C2 to be subjected to differential amplification with the differential amplifier U1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermo-sensitive flow velocity measuring device which is used in a gas flow meter, a flow meter, etc., and measures a flow velocity by a temperature change of a resistance caused by a fluid.

[0002]

2. Description of the Related Art Such a flow velocity measuring device is disclosed, for example, in Japanese Patent Application Laid-Open No. 10-206205.

[0003]

FIG. 3 shows an example of the configuration of a flow measuring device. This flow rate measuring device is roughly composed of a sensor driving unit 1, a difference voltage detecting unit 2, and an amplifying unit 3. In the sensor driving section 1, a first temperature-sensitive resistor RS1 and a second temperature-sensitive resistor RS2 mounted on a sensor substrate (not shown) provided in a flow path are provided. I have. These first and second temperature-sensitive resistors RS
1 and RS2 are also exposed to the fluid. Here, it is assumed that the positional relationship is set such that the first temperature-sensitive resistor RS1 is on the upstream side and the second temperature-sensitive resistor RS2 is on the downstream side. I do. In addition, these first and second temperature-sensitive resistors RS1,
RS2 having the same resistance value and a high resistance temperature coefficient is used. These first and second temperature-sensitive resistors RS1 and RS2 are connected to a current source 4 acting as a heating device.
And are connected in series. That is, the current source 4 causes the first and second temperature-sensitive resistors RS1 and RS2 to be equally heated so that the current I1 flows to generate Joule heat in the resistor itself so that the temperature becomes higher than the fluid temperature. (However, the first and second temperature-sensitive resistors RS1 and RS2 may be heated by separate heat sources as a heating device.) Also, in the sensor driving section 1, both ends b and c of the second temperature-sensitive resistor RS2 are connected in a feedback loop, the current source 4 and the first
And an operational amplifier 6 connected to the output side of a connection point a with the temperature-sensitive resistor RS1.

The differential voltage detecting section 2 functions as a detecting device. The terminal voltage (= output at point f) of the first temperature-sensitive resistor RS1 output from the operational amplifier 6 to the point d and the point c from the operational amplifier 5 to the point c. (= Point e) the second temperature-sensitive resistor R output
An adder 7 is provided which outputs a difference voltage from the terminal voltage of S2 (= output at point h) to point g.

The amplifier 3 amplifies 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. 10 is provided.

In such a configuration, the heat of the first and second temperature-sensitive resistors RS1 and RS2 is removed by the flow of the fluid. The amount of heat deprived is related to the flow of the fluid. For example, if there is no flow in the fluid, the temperatures of the first and second temperature-sensitive resistors RS1 and RS2 are substantially equal, and the resistance values are also substantially equal. Therefore, the terminal voltage of the first temperature-sensitive resistor RS1 is substantially equal to the terminal voltage of the second temperature-sensitive resistor RS2, and the output at the point g of the differential voltage detecting unit 2 is also substantially zero. On the other hand, when there is a flow in the fluid, the heat of the first temperature-sensitive resistor RS1 on the upstream side is removed more than on the downstream side, so that 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 becomes smaller than that on the downstream side. Therefore, the terminal voltage of the first temperature-sensitive resistor RS1 becomes lower than the terminal voltage of the second temperature-sensitive resistor RS2. The difference between the terminal voltages 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 difference voltage detecting unit 2. When an A / D converter or the like is used to measure these terminal voltages, difference voltages, etc.
Since it is necessary to convert the signal into a voltage signal suitable for a D converter or the like, the amplifying unit 3 is provided at a subsequent stage.

However, the device shown in FIG. 3 uses a plurality of operational amplifiers, consumes a large amount of power, and cannot be driven for a long time by a battery.

An object of the present invention is to provide a flow measuring device suitable for driving with a battery power supply by suppressing power consumption.

Another object of the present invention is to enable more accurate information on temperature compensation of the flow velocity of a fluid to be obtained.

Another object of the present invention is to enable continuous flow rate information to be output.

Another object of the present invention is to enable timely output of fluid temperature information.

[0012]

According to a first aspect of the present invention, a flow rate of the fluid is measured from a terminal voltage difference between two temperature-sensitive resistors which are respectively disposed on the upstream side and the downstream side of the fluid and heats. In the flow velocity measuring device, the two voltage holding devices that follow the terminal voltage of each of the temperature sensitive resistors and hold the voltages, an amplifier, and one terminal voltage of the temperature sensitive resistor can be amplified by the amplifier. And a first switch capable of switching a line connection state so that a difference between voltages held by the two voltage holding devices can be amplified by the amplifier. It is a measuring device.

Therefore, if the voltage held by the two voltage holding devices is set to a common potential, for example, a voltage with reference to GND, and the difference between the voltages held by the two voltage holding devices is amplified by the amplifier, the fluid Can be measured. Since the present device has a circuit configuration using only a single amplifier, power can be saved, and the device is suitable for driving with a battery power supply. Further, by amplifying the voltage held by one of the voltage holding devices by an amplifier, the temperature of the fluid can be detected, and information on temperature compensation of the flow velocity of the fluid can be obtained.

According to a second aspect of the present invention, there is provided a flow velocity measuring apparatus for measuring a flow velocity of a fluid from a terminal voltage difference between two temperature-sensitive resistors arranged and heated on an upstream side and a downstream side of the fluid, respectively. Two voltage holding devices that follow the terminal voltage of each of the temperature-sensitive resistors and hold the voltages, an amplifier,
A temperature measuring resistor for measuring the temperature of the fluid, and the difference between voltages held by the two voltage holding devices is also amplified by the amplifier so that the voltage between terminals of the temperature measuring resistor can be amplified by the amplifier. And a first switch capable of switching the connection state of the line as much as possible.

Accordingly, if the voltage held by the two voltage holding devices is set to a common potential, for example, a voltage with reference to GND, and the difference between the voltages held by the two voltage holding devices is amplified by the amplifier, the fluid Can be measured. Since the present device has a circuit configuration using only a single amplifier, power can be saved, and the device is suitable for driving with a battery power supply. In addition, the temperature of the fluid is detected by amplifying the voltage between the terminals of the resistance temperature detector by the amplifier, and the information of temperature compensation of the flow velocity of the fluid can be obtained more accurately.

According to a third aspect of the present invention, in the flow rate measuring device according to the first or second aspect, a second switch for opening and closing a line for supplying power to a circuit of the device is provided. I do.

Therefore, when it is not necessary to measure the flow velocity, the power supply to the circuit can be stopped, so that the driving with the battery power supply becomes easy.

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 amplifier can change an amplification factor.

Therefore, it is possible to amplify the voltage difference between the two temperature-sensitive resistors and to amplify the terminal voltage of the temperature-sensitive resistor or the terminal voltage of the temperature-measuring resistor using the same amplifier. Flow velocity measurement and temperature measurement can be performed without any power consumption.

According to a fifth aspect of the present invention, in the flow velocity measuring apparatus according to any one of the first to fourth aspects, the voltage holding device follows the terminal voltage of each of the temperature-sensitive resistors to follow the voltage. And a third switch capable of switching a line connection state so that the voltage held by the voltage holding device can be applied to the amplifier.

Therefore, the measurement of the terminal voltage of each temperature sensing resistor and the measurement of the flow velocity of the fluid can be alternately repeated, and continuous flow velocity information can be output.

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, a current source for supplying a current to the temperature-sensitive resistor is provided, and It is characterized in that the current can be stopped or reduced.

Therefore, power consumption when there is no need to measure the flow velocity is suppressed, and driving with a battery power source is facilitated.

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 is amplified by the amplifier by switching the first switch. When the current source is enabled, a current control means for stopping or reducing the current supplied from the current source to the temperature-sensitive resistor is provided.

Therefore, power consumption when the flow velocity measurement is not performed is suppressed, and driving with a battery power source is facilitated.

According to an eighth aspect of the present invention, there is provided the flow velocity measuring device according to any one of the first to seventh aspects, wherein the first
A temperature measuring means for switching one of the switches as appropriate to enable the amplifier to amplify one terminal voltage of the temperature sensing resistor or the terminal voltage of the temperature measuring resistor.

Therefore, it is possible to output the temperature information of the fluid in a timely manner.

According to a ninth aspect of the present invention, in the flow velocity measuring apparatus according to the third aspect, the two voltage holding devices follow the terminal voltages of the respective temperature-sensitive resistors to hold the voltages. An operation of switching a first switch to amplify one terminal voltage of the temperature-sensitive resistor or the terminal voltage of the temperature-measuring resistor by the amplifier, and a difference between voltages held by the two voltage holding devices. And an operation of switching the second switch to open a line for supplying power to the circuit of the device as appropriate.

Therefore, intermittent flow velocity measurement can be performed, power consumption during a period in which flow velocity measurement is not required is suppressed, and driving with a battery power source is facilitated.

According to a tenth aspect of the present invention, in the flow velocity measuring device according to the first or second aspect, the operation of causing the two voltage holding devices to follow the terminal voltages of the respective temperature sensitive resistors and hold the voltages. And a simultaneous execution means for simultaneously switching the first switch and amplifying one terminal voltage of the temperature-sensitive resistor or the terminal voltage of the temperature-sensitive resistor by the amplifier. And

Therefore, the measurement of the flow velocity and the measurement of the fluid temperature are performed at the same time, the time required for these measurements is reduced, the power consumption is suppressed, and the driving with the battery power source becomes easy.

[0032]

[First Embodiment of the Invention] FIG.
1 is a circuit diagram of a flow velocity measuring device according to a first embodiment 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. These temperature sensitive resistors Ru, Rd
Has a high temperature coefficient of resistance such as platinum, has the same resistance value and temperature coefficient of resistance, has the same shape, and has the same thermal characteristics such as heat radiation.

The current source Ih supplies a 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 the node A. Temperature sensitive resistor Rd
Is connected to one end of the temperature-sensitive resistor Ru at a node B. The other end of the temperature-sensitive resistor Ru is grounded.

Symbols C1 and C2 are capacitors which are voltage holding devices. The symbol U1 is a differential amplifier which is an amplifier. Symbols SW1, SW2, SW3, SW4, SW5 and S
W6 is a switch, such as a semiconductor switch, whose opening and closing can be controlled by an electric signal. Switches SW5 and SW6 constitute a first switch. Switch S
W1, SW2, SW3, and SW4 constitute a third switch.

The control signal S1 includes switches SW1, SW2, S
This is a signal for controlling the opening and closing of W3 and SW4. The control signal S2 is a signal for controlling the 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.

The control signal S1 is a signal for switching between two types of states, a following state and a holding state. In the following state, the switch SW1 connects the node D at one end of the capacitor C1 to the node A at one end of the temperature sensitive resistor Rd, and the switch SW2 connects the node E at 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 node F at one end of the capacitor C2 to the node B at one end of the temperature-sensitive resistor Ru, and the switch SW4 connects the node G at the other end of the capacitor C2 to the temperature-sensitive resistor R
Connect the C node at the other end of u. In the holding state, the switch S
W1 connects the D node and the H node at one end of the capacitor C1, and the switch SW2 connects the E node and the I node 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 capacitor C2.
Connect the G and I nodes at the other end of 2. 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-sensitive resistor Rd to the non-inverting input terminal of the differential amplifier U1, and the switch SW6 is connected to the node B at the other end of the temperature-sensitive resistor Rd. Connect to the inverting input terminal of amplifier U1.
In the flow velocity measurement state, the switch SW5 connects the node H to the non-inverting input terminal of the differential amplifier U1, and the switch SW6 connects the node J to the inverting input terminal of the differential amplifier U1.

The control signal S4 is a signal for switching between a heating state and a standby state. In the heating 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.

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 gain of the differential amplifier U1 is reduced, for example, to one. In the minute voltage state, the amplification factor of the differential amplifier U1 is large, for example, 40 times.

The control signal S5 controls the power to the circuit of FIG.
N / OFF signal. 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 in 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.

Next, the operation of the flow velocity measuring device having the above configuration will be described. The circuit of FIG. 1 is turned off by the control signal S5.
When in the F state, the circuit does not operate because it has been powered down. This is hereinafter referred to as a pause period. During this idle period, the supply of power from the power supply to the circuit of FIG. 1 is at a minimum.

Next, the control signal S5 is turned on, the control signal S1 is followed, the control signal S4 is heated, and the control signal S5 is turned on.
The 2 and S3 signals are set to an arbitrary state. This is hereinafter referred to as a flow velocity measurement period. When the power is supplied, the circuit of FIG. 1 becomes operable, and the current source Ih supplies the current to the temperature-sensitive resistor element R.
u, Rd. The temperature-sensitive resistors Ru and Rd generate heat by the current supplied by the current source Ih. Temperature sensitive resistor Ru
And the terminal voltage generated at Rd are switches SW1, SW2,
After passing through SW3 and SW4, they are stored in capacitors C1 and C2, respectively. Thereby, the terminal voltage of the temperature-sensitive resistor Ru, the terminal voltage of the capacitor C1, the temperature-sensitive resistor Rd
Is equal to the terminal voltage of the capacitor C2.

After a lapse of time sufficient 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 the minute voltage state. This is hereinafter referred to as a flow velocity output period. Differential amplifier U
1 has a high input impedance, the capacitors C1 and C
2 holds the terminal voltages of the temperature-sensitive resistors Rd and Ru, respectively. E side of capacitor C1 and G of capacitor C2
Since the node side is grounded via the switches SW2 and SW4, the voltage value of the temperature-sensitive resistor Rd based on the ground point appears in the node H, and the temperature-sensitive resistor Ru based on the ground point appears in the node J.
Voltage value 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 difference between the voltages of the nodes H and J, that is, the value obtained by subtracting the terminal voltage of the temperature-sensitive resistor Ru from the terminal voltage of the temperature-sensitive resistor Rd is amplified and output to the node O on the output side of the differential amplifier U1. Is done.

When the control signal S5 is in the ON state and the control signal S4 is in the heating state, the control signal S2 is set to the temperature measurement state, and the control signal S3 is set to the normal voltage state. The terminal voltage of the thermal resistor Rd is output. This implements a temperature measuring means. This is hereinafter referred to as a temperature output period.

During the flow velocity measurement period, the temperature sensitive resistors Ru and Rd generate heat by 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 and generates heat in the same manner even in the state of heat generation, so that the resistance values are equal. 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, the process proceeds 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 difference voltage 0 is input to the differential amplifier U1. Therefore, the output of the differential amplifier U1 becomes zero.

When there is a flow in the fluid, the heat generated by the temperature sensitive resistors Ru and Rd is removed by the fluid during the flow velocity measurement period. However, the temperature-sensitive resistor Rd is different from the temperature-sensitive resistor Ru.
The heat taken from the temperature-sensitive resistor Ru is transferred to the temperature-sensitive resistor Rd. Therefore, the temperature sensitive resistor Rd loses less heat than the temperature sensitive resistor Ru.
When the heat is removed, 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 becomes smaller than the terminal voltage value of the temperature-sensitive resistor Rd. This difference in voltage is related to the flow rate of the fluid, and increases as the flow rate increases. This voltage is applied to the capacitors C1 and C2.
Stored in Next, the process proceeds 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.
The voltage of 2 is applied to the inverting input terminal of the differential amplifier U1. The difference between the voltages of capacitors C1 and C2 is determined by differential amplifier U1.
And appear at the output. That is, an output related to the flow velocity is obtained.

When the fluid is flowing backward, the temperature-sensitive resistor R
u 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 in the upstream and downstream directions. In other words, it appears in the output during the flow velocity output period with a sign opposite to that of the normal flow. Therefore, the sign of the output signal during the flow velocity output period can be used to determine whether the fluid flows forward or backward. Then, by alternately repeating the flow velocity measurement period and the flow velocity output period, continuous flow velocity measurement can be performed.

During the temperature measurement period, the terminal voltage of the temperature sensitive resistor Rd is applied to the differential input of the differential amplifier U1. Therefore, the terminal voltage of the temperature sensitive resistor Rd is amplified and output. The resistance value of the temperature-sensitive resistor Rd changes according to the temperature of the fluid. That is, the terminal voltage of the temperature-sensitive resistor Rd has a value related to the temperature of the fluid. Differential amplifier U during temperature measurement
The output of 1 makes it possible to know the temperature of the fluid. This value makes it possible to correct the temperature dependency in the flow velocity measurement.

As described above, continuous flow velocity measurement can be performed by appropriately switching the flow velocity measurement period, the flow velocity output period, and the temperature measurement period.

The control signal S5 is turned on, the control signal S1 is followed, the control signal S4 is heated, and the control signal S5 is turned on.
2 is set to a temperature measurement state, and the control signal S3 is set to a 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 changed to the differential amplifier U1.
And the amplified terminal voltage of the temperature-sensitive resistor Rd is output to the node O. That is, the flow velocity measurement period and the temperature measurement period are performed simultaneously. This implements a 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.
Power consumption can be reduced. When it is not necessary to measure the flow velocity, the power consumption can be suppressed by setting the idle period. As a result, a pause unit is realized. During the flow speed output period, the current source Ih is stopped or the current value is reduced by the control signal S4. This implements current control means.

Here, for example, if the temperature-sensitive resistors Ru and Rd are formed by a micro-bridge sensor formed on a silicon substrate as disclosed in JP-A-10-206205, the micro-bridge sensor has a minute structure. Since the heat is generated until the flow velocity can be measured with a small amount of electric power, the flow rate sensor can save power.

The temperature sensitive resistors Ru and Rd by the microbridge are set to, for example, about 500Ω at room temperature. When a current of, for example, 1.75 mA is passed as the current source Ih, the temperature-sensitive resistor Ru
And Rd generate heat at about 100 ° C. At this time, the terminal voltages of the temperature sensitive resistors Ru and Rd are about 1.2V. When a flow occurs in the fluid, a slight difference occurs between the terminal voltages of the temperature-sensitive resistors Ru and Rd. The difference occurs up to about 60 mV. If the flow of the flow velocity is too fast, no difference appears between the heat taken by the temperature-sensitive resistors Ru and Rd. Therefore, the difference between the terminal voltages of the temperature-sensitive resistors Ru and Rd due to the flow velocity increases as the flow velocity increases. It gradually saturates 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 device is driven by a battery or the like, the output is desired to have a value of about 0 to 3V. During the temperature measurement period, the terminal voltage of the temperature-sensitive resistor Rd is amplified and output at about 1.2 V, so that the amplification factor of the differential amplifier U1 is 1-2.
You can double it. In the flow velocity output period, the temperature-sensitive resistor R
Since the voltage difference between u and Rd is amplified by about 60 mV, the amplification factor of the differential amplifier U1 may be about 50 times. When it is desired to measure the reverse current with a single power supply, the offset can be shifted by shifting the output offset of the differential amplifier U1 in the positive voltage direction.

[Embodiment 2] FIG. 2 is a circuit diagram of a flow velocity measuring apparatus according to Embodiment 2 of the present invention. 2, the same reference numerals as those in FIG. 1 denote the same circuit elements and the like as in the first embodiment of the invention, and a detailed description thereof will be omitted.

In the first embodiment of the present invention, the terminal voltage of the temperature-sensitive resistor Rd is output during the temperature measurement period to obtain a fluid temperature signal. According to the second embodiment of the present invention, since the temperature-sensitive resistor Rd changes its voltage under the influence of the flow velocity, the temperature-measuring resistor Rf for measuring the temperature of the fluid is changed to the temperature-sensitive resistor in order to perform more accurate temperature measurement. This is an example provided separately from the bodies Ru and Rd.

The temperature measuring resistor Rf is a resistor having a large temperature coefficient of resistance, such as platinum. The temperature measuring resistor Rf is installed at a position which is not affected by the heat generated by the temperature sensing resistors Ru and Rd in the fluid. The resistance temperature detector Rf is connected to the current source If.

In the temperature measurement state according to the first embodiment of the present invention, the switches SW5 and SW6 are switched so that the terminal voltage of the temperature sensitive resistor Rd is differentially input to the differential amplifier U1. In the second embodiment, the resistance thermometer R
The terminal voltage of f 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.

When the temperature measuring resistor 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 accurately obtained. The resistance value of the resistance bulb Rf is set to, for example, about 5 kΩ at room temperature, and a current of about 100 μA flows from the current source If. Then, the terminal voltage of the resistance bulb Rf becomes about 0.5V.
This voltage varies in relation to 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.

Note that the resistance value and the amplification factor shown in each embodiment of the present invention are merely examples, and other values may be used. These are designed in accordance with the available power supply voltage, the characteristics of the temperature sensing resistor, the characteristics of the temperature measuring resistor, and the characteristics of the fluid to be measured.

[0058]

According to the first aspect of the present invention, the voltages held by the two voltage holding devices are set to a common potential, for example, a voltage based on GND, and the voltages held by the two voltage holding devices are respectively set. If the difference is amplified by an amplifier, the flow velocity of the fluid can be measured. Since the present device has a circuit configuration using only a single amplifier, power can be saved, and the device is suitable for driving with a battery power supply. Further, by amplifying the voltage held by one of the voltage holding devices by an amplifier, the temperature of the fluid can be detected, and information on temperature compensation of the flow velocity of the fluid can be obtained.

According to a second aspect of the present invention, the voltages held by the two voltage holding devices are set to a common potential, for example, a voltage with reference to GND, and the difference between the voltages held by the two voltage holding devices is determined. If amplified by an amplifier, the flow velocity of the fluid can be measured. Since the present device has a circuit configuration using only a single amplifier, power can be saved, and the device is suitable for driving with a battery power supply. In addition, the temperature of the fluid is detected by amplifying the voltage between the terminals of the resistance temperature detector by the amplifier, and the information of temperature compensation of the flow velocity of the fluid can be obtained more accurately.

According to a third aspect of the present invention, in the flow rate measuring device according to the first or second aspect, the power supply to the circuit can be stopped when it is not necessary to measure the flow velocity, so that the apparatus is driven by a battery power supply. Becomes easier.

According to a fourth aspect of the present invention, there is provided the flow rate measuring device according to any one of the first to third aspects, wherein the amplification of the voltage difference between the two thermosensitive resistors and the amplification of the terminal voltage of the thermosensitive resistors are performed. Alternatively, the terminal voltage of the resistance bulb can be amplified by the same amplifier, so that the flow velocity measurement and the temperature measurement can be performed without increasing the number of amplifiers, and power consumption can be suppressed.

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 alternately performed. It is possible to repeat and output continuous flow rate information.

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, power consumption when flow velocity measurement is not required is suppressed, and driving with a battery power supply is performed. It will be easier.

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 is not measured is suppressed, and driving with a battery power source is facilitated.

According to an eighth aspect of the present invention, in the flow velocity measuring apparatus according to any one of the first to seventh aspects, it is possible to output timely fluid temperature information.

According to a ninth aspect of the present invention, in the flow velocity measuring device according to the third aspect, the intermittent flow velocity measurement can be performed, and the power consumption during the period in which the flow velocity measurement is not required can be suppressed. Driving becomes easier.

According to a tenth aspect of the present invention, in the flow velocity measuring device according to the first or second aspect, the measurement of the flow velocity and the measurement of the fluid temperature are simultaneously performed to reduce the time required for the measurement and the power consumption. Thus, driving with a battery power source is facilitated.

[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 device 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 sensing resistor Ih Current source C1, C2 Voltage holding device U1 Amplifier SW1 to SW4 Third switch SW5, SW6 First switch Rf Resistance thermometer

Claims (10)

[Claims] 1. A flow rate measuring device for measuring a flow rate of a fluid from a terminal voltage difference between two temperature sensitive resistors which are respectively arranged on an upstream side and a downstream side of a fluid and heats the fluid, Two voltage holding devices that follow the terminal voltage and hold the voltage; an amplifier; and the two voltage holding devices respectively hold so that one terminal voltage of the temperature-sensitive resistor can be amplified by the amplifier. And a first switch capable of switching the connection state of the line so that the difference between the voltages can be amplified by the amplifier. 2. A flow rate measuring device for measuring a flow rate of a fluid from a terminal voltage difference between two temperature sensitive resistors which are respectively arranged on an upstream side and a downstream side of a fluid and heats the fluid, Two voltage holding devices that follow the terminal voltage and hold the voltage, an amplifier, a temperature measuring resistor that measures the temperature of the fluid, and a terminal voltage of the temperature measuring resistor that can be amplified by the amplifier. And a first switch capable of switching a connection state of a line so that a difference between voltages held by the two voltage holding devices can be amplified by the amplifier. . 3. The flow measuring device according to claim 1, further comprising a second switch for opening and closing a line for supplying power to a circuit of the device. 4. The flow measuring device according to claim 1, wherein the amplifier can change an amplification factor. 5. A line for allowing the voltage holding device to follow the terminal voltage of each of the temperature-sensitive resistors and hold the voltage, or apply the voltage held by the voltage holding device to the amplifier. A third switch capable of switching a connection state is provided.
The flow velocity measuring device according to any one of the above. 6. The device according to claim 1, further comprising a current source for supplying a current to the temperature-sensitive resistor, wherein the current source can stop or reduce the current. Flow velocity measuring device. 7. 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 source is connected to the temperature-sensitive resistor. 7. The flow velocity measuring device according to claim 6, further comprising current control means for stopping or reducing the supplied current. 8. A temperature measuring means for switching the first switch as appropriate to enable one terminal voltage of the temperature sensitive resistor or the terminal voltage of the temperature measuring resistor to be amplified by the amplifier. The flow velocity measuring device according to any one of claims 1 to 7, characterized in that: 9. An operation in which the voltage holding devices follow the terminal voltage of each of the temperature-sensitive resistors to hold the voltage, and the first switch is switched to switch one terminal voltage of the temperature-sensitive resistor. The operation of amplifying the terminal voltage of the resistance temperature detector by the amplifier, the operation of amplifying the difference between the voltages held by the two voltage holding devices by the amplifier, and the second switch, The flow velocity measuring apparatus according to claim 3, further comprising a pause unit for appropriately switching between an operation of opening a line for supplying power to a circuit of the apparatus and an operation of opening the line. 10. An operation of causing the voltage holding devices to follow a terminal voltage of each of the temperature-sensitive resistors and holding the voltage, and a voltage of one terminal of the temperature-sensitive resistor by switching the first switch. 3. The flow velocity measuring device according to claim 1, further comprising a simultaneous execution unit that simultaneously performs an operation of amplifying a terminal voltage of the resistance temperature detector by the amplifier. 4.