JP4575548B2 - Thermal flow meter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thermal flow meter, and more particularly, to a thermal flow meter having a wide and highly accurate measurement range.
[0002]
[Prior art]
In general, a thermal flow meter supplies driving power to a heater in a fluid that has a heater disposed upstream of the fluid to be measured and a resistor disposed downstream from the heater at a predetermined interval. The flow rate is measured by measuring the resistance value of the resistor when generating heat and the function of the flow rate and the resistance value of the resistor is stored in advance, and the flow rate is measured using the function. .
[0003]
In the flow rate measurement, a wide measurable range from a very small flow rate to a high flow rate is required for the fluid to be measured. However, in the above-described configuration using only one set of heater and resistor, the range that can be measured with a certain level of accuracy is limited. For example, there is a problem that sufficient measurement accuracy cannot be obtained at a minute flow rate.
[0004]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and is a thermal type capable of obtaining a wide measurement range with high accuracy by properly using a heater and a resistor according to the flow rate of a fluid to be measured. The object is to provide a flow meter.
[0006]
The invention of claim 1 has a flow sensor comprising a heater and a resistor disposed on the heat conductor downstream of the heater at a predetermined interval from the heater, and supplies driving power to the heater. In the thermal type flow meter that measures the flow rate of the fluid to be measured based on the change in the resistance value of the resistor when the heat is generated, the flow sensor includes a heater on the first base portion by the heat conductor. And a first flow sensor provided with a first resistor, and a second flow sensor provided with a second resistor on a second base portion made of a heat conductor, the first base body An end portion of the portion and an end portion of the second base portion are arranged in contact with each other upstream of the fluid to be measured, and the heat of the heater is propagated to the second flow sensor, thereby The second flow sensor has a heater with a lower capacity than the heater. If the fluid to be measured has a flow rate higher than a predetermined unit flow rate value, the first flow sensor is based on the first flow sensor. If the flow rate is adopted and the flow rate is lower than the unit flow rate value, the flow rate based on the second flow sensor is adopted to obtain the flow rate of the fluid to be measured.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
( Reference Example 1)
FIG. 1 is a schematic configuration diagram for explaining a first reference example of a thermal flow meter according to the present invention, in which 10 is a first flow sensor, 11 is a first heater, and 12 is a first flow sensor. A resistor, 13 is a first substrate, 20 is a second flow sensor, 21 is a second heater, 22 is a second resistor, 23 is a second substrate, and F is a flow direction of the fluid to be measured. .
[0009]
As shown in FIG. 1, the thermal flow meter of the present reference example has a first heater 11 and a first resistor having a predetermined capacity spaced apart from each other on a first base 13 made of a good thermal conductor by a predetermined distance. The first flow sensor 10 and the second heater 21 and the second resistor 22 having a capacity smaller than that of the first heater 11 are spaced apart from each other on the second base 23 of a good heat conductor by a predetermined distance. And a control unit (not shown) for calculating the flow rate of the fluid to be measured based on the resistance values of the resistors 12 and 22 of the flow sensors 10 and 20. is doing. The first and second bases 13 and 23 are made of a good heat conductor, and an insulating film (not shown) is provided on the surface, and the heaters 11 and 21 and the resistors 12 and 22 are arranged.
[0010]
The thermal flow meter of this reference example can obtain a wide measurement range with high accuracy by properly using the two flow sensors 10 and 20 according to the flow range of the fluid to be measured. In this reference example, the first flow sensor 10 is used for high flow range measurement and the second flow sensor 20 is used for low flow range (micro flow range) measurement. The lower flow rate range is set to the above-described low flow rate range, and the higher flow rate range is set to the above-described high flow rate range), and the heater and resistor specifications of each flow sensor are determined in accordance with the set values.
[0011]
Each heater of each flow sensor 10, 20 operates continuously or intermittently according to a predetermined condition, and outputs the resistance value of each resistor 12, 22. In a control unit (not shown), the resistance values of the resistors 12 and 22 are input, and the flow rate is calculated based on a function of the flow rate and the resistance value held in advance. The flow sensor to be employed is determined based on the above-described target flow rate range of the flow sensor, and the flow rate obtained by the flow sensor is set as the measurement flow rate of the thermal flow meter. With the above configuration, it is possible to measure the flow rate with high accuracy in a wide measurement range.
[0012]
( Example)
Figure 2 is a side schematic diagram for explaining the actual施例of the thermal type flow meter according to the present invention, in the figure, 30 is a flow sensor, 31 is a heater, the first resistor 32, the 33 second The resistor 34a is a first base portion, and 34b is a second base portion. Note that an insulating film (not shown) is provided on the surface of each of the base portions 34a and 34b as in the first embodiment.
[0013]
The thermal flow meter of the present embodiment has one heater 31 and two resistors 32 on the first and second base portions 34a and 34b of the good heat conductor that are in contact with each other on the upstream side of the fluid to be measured. A flow sensor 30 having a predetermined interval 33 and a control unit (not shown) for calculating the flow rate of the fluid to be measured based on the resistance values of the resistors 32 and 33; Yes. In the present embodiment, a wide measurement range can be obtained with high accuracy by properly using the two resistors 32 and 33 in accordance with the flow rate range of the fluid to be measured.
[0014]
In the present embodiment, the first resistor 32 is used for measuring a high flow rate range, and the second resistor 33 is used for measuring a low flow rate range (micro flow rate range). / H or less is set as the above low flow rate range, and the above is set as the above high flow rate range), and the specifications of the heater 31 and the respective resistors 32 and 33 are determined in accordance with the set value.
[0015]
The flow sensor of the present embodiment performs heating using one heater 31 disposed on the first base portion 34a, and measures the flow rate by the resistance value of the first resistor 32 in the high flow rate range. Further, in the low flow rate range, the heat of the heater 31 is propagated to the second base portion 34b, and the flow rate is measured using the resistance value of the second resistor. Here, since the distance between the heater 31 and the second resistor 33 is long, apparently different temperature settings are possible. That is, by propagating heat from the heater 31, the effect is as if a heater having a smaller capacity than the heater 31 is provided on the second base portion 34b.
[0016]
The heater 31 operates continuously or intermittently according to a predetermined condition, and the resistance values of the resistors 32 and 33 are output. In a control unit (not shown), the resistance values of the resistors 32 and 33 are input, and the flow rate is calculated based on a function of the flow rate and the resistance value held in advance. The flow sensor to be employed is determined based on the above-described target flow rate range of the flow sensor, and the flow rate obtained by the flow sensor is set as the measurement flow rate of the thermal flow meter. With the above configuration, it is possible to measure the flow rate with high accuracy in a wide measurement range.
[0017]
The first base portion 34a for measuring a high flow rate is set obliquely with respect to the flow direction of the fluid to be measured (for example, 30 ° with respect to the flow direction), and the cooling efficiency in the high flow rate range. The second base portion 34b for measuring a low flow rate is arranged in parallel to the fluid flow direction. With such a configuration, a predetermined level of measurement accuracy can be obtained in each flow rate range. The arrangement angles of the base portions 34a and 34b are limited as described above as long as measurement accuracy can be ensured according to the specifications of the heater 31 and the resistors 32 and 33 and the physical properties of the fluid or the flow range of the fluid. It can set suitably, without.
[0018]
( Reference Example 2 )
FIG. 3 is a diagram for explaining a second reference example of the thermal type flow meter of the present invention, in which 40 is a flow sensor, 41 is a first heater, and 42 is smaller in capacity than the first heater. The second heater 43 is a first resistor, 44 is a second resistor, and 45 is a base. Note that an insulating film (not shown) is provided on the surface of the base body 45 as in Reference Example 1 and Examples . The thermal flow meter of this reference example includes a flow sensor 40 in which two heaters 41 and 42 and two resistors 43 and 44 are disposed on a base 45 on a good heat conductor with a predetermined interval; And a control unit (not shown) for calculating the flow rate of the fluid to be measured based on the resistance values of the resistors 43 and 44. In this reference example, the two heaters 41 and 42 are switched by the switch S according to the flow range of the fluid to be measured, and the flow rate is calculated based on the resistance value of the resistor set corresponding to the heater. Thus, a wide measurement range can be obtained with high accuracy.
[0019]
In the thermal flow meter of this reference example, a set of the first heater 41 and the second resistor 44 is used for high flow range measurement, and the second heater 42 and the first heater 42 having a lower heat capacity than the first heater 41 are used. The set with the resistor 43 is used for measuring a low flow rate range (micro flow rate range), and the target flow rate range (for example, 100 l / h or less is set as the low flow rate range and the higher flow rate is set as the high flow rate). Range) and the specifications of the heaters 41 and 42 and the resistors 43 and 44 are determined in accordance with the set values.
[0020]
In this reference example, the control unit uses each set of the heater and the resistor by switching according to the flow rate of the fluid to be measured. That is, in this reference example, in the flow rate range equal to or larger than a predetermined amount, the first heater 41 is supplied with driving power to generate heat, and the resistance of the second resistor 44 corresponding to the first heater 41 is increased. The value is read, and the flow rate is calculated by a function held in advance by the control unit based on the resistance value. On the other hand, in a range smaller than the predetermined amount (small flow rate range), the second heater 42 is used to generate heat, and the flow rate is measured from the resistance value of the corresponding first resistor 43.
[0021]
【The invention's effect】
As is apparent from the above description, according to the present invention, a thermal flow rate capable of obtaining a wide measurement range with high accuracy by properly using a heater and a resistor according to the flow rate of the fluid to be measured. A total can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic plan view illustrating a first reference example of a thermal flow meter according to the present invention.
2 is a side schematic diagram for explaining the actual施例of the thermal type flow meter according to the present invention.
FIG. 3 is a schematic plan view illustrating a third reference example of the thermal type flow meter according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... 1st flow sensor, 11 ... 1st heater, 12 ... 1st resistor, 13 ... 1st base | substrate, 20 ... 2nd flow sensor, 21 ... 2nd heater, 22 ... 2nd Resistor, 23 ... second substrate, 30 ... flow sensor, 31 ... heater, 32 ... first resistor, 33 ... second resistor, 34a ... first substrate portion, 34b ... second substrate portion , 40 ... Flow sensor, 41 ... First heater, 42 ... Second heater, 43 ... First resistor, 44 ... Second resistor, 45 ... Base, F ... Flow direction of fluid to be measured, S …switch.

Claims (1)

A flow sensor comprising a heater and a resistor disposed on the heat conductor downstream of the heater at a predetermined interval on the heat conductor, when driving power is supplied to the heater to generate heat; In the thermal flow meter for measuring the flow rate of the fluid to be measured based on the change in the resistance value of the resistor,
The flow sensor includes a first flow sensor including a heater and a first resistor on a first base portion made of a heat conductor, and a second resistor on a second base portion made of a heat conductor. And an end portion of the first base portion and an end portion of the second base portion are arranged in contact with each other on the upstream side of the fluid to be measured,
By propagating the heat of the heater to the second flow sensor, the second flow sensor acts as if a heater having a lower capacity than the heater exists, and the first and second If the fluid to be measured has a flow rate higher than a predetermined unit flow rate value, the flow rate based on the first flow sensor is adopted and the flow rate is lower than the unit flow rate value. For example, a flow rate based on the second flow sensor is adopted to obtain the flow rate of the fluid to be measured.

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