JPH05107093A - Thermal flowmeter - Google Patents

Abstract

PURPOSE:To quickly and easily measure the flow of arbitrary fluid without conducting calibration on each part of a device by measuring the heat capacity of the flow on the basis of an acumulated heat capacity and temperature change for the fluid within a tube in a stop state. CONSTITUTION:With a heater 2 heated, a measurement-intended fluid Sa within a tube 1 is heated, and the temperature after a specified time is detected by the use of a downstream side temperature detection sensor 7. It is input to a heat capacity measurement circuit 5 in order to determine a heat capacity Ca which is then output to a physical properties modifying circuit 10. Within the circuit 10 operation is performed in response to the heat capacity Ca, a factor Ka representing the physical properties of fluid Sa to be measured is determined. Within a flow operation circuit 4 a factor Ka is set in place of a calibration factor Kf determined for standard fluid Sf as a reference for flow rate calculation. Thereby, it is not necessary to conduct calibration at each part of a device every time when the fluid is exchanged and the flow rate of arbitrary fluid can be easily measured in a short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal type flow meter for detecting a temperature difference generated in a fluid and measuring the flow rate of the fluid.

[0002]

2. Description of the Related Art As an example of a conventional thermal type flow meter, a heater is provided on a pipe through which a fluid is passed, and upstream and downstream temperature detecting sensors are provided on the upstream side and the downstream side of the heater, respectively.
In addition, there is a device provided with an arithmetic means for obtaining the flow rate of the fluid passing through the pipe based on the amount of heat applied to the fluid by the heater, the temperature difference detected by both temperature detection sensors, and the physical property data of the fluid. This thermal type flow meter heats the fluid flowing in the pipe with a heating element, and at that time, the upstream and downstream temperature sensors detect the temperature, the heating amount to the fluid, the temperature difference between the temperature detection sensors, and the fluid. The flow rate (mass flow rate) of the fluid is measured based on the physical property data.

[0003]

By the way, it is desired that the thermal type flow meter can measure the flow rate quickly and easily for various fluids. However, in the above-mentioned thermal type flow meter, when measuring the flow rates of different kinds of fluids,
Prior to flow rate measurement, each member and setting data, etc. should be calibrated in advance corresponding to the physical property data of the fluid, and then flow meter rule shall be carried out, and flow meter rule of many kinds of fluid shall be carried out. However, since it takes a lot of time to calibrate each part for each fluid, it is the actual situation that the above-mentioned demand cannot be met.

As a measure for measuring the flow rates of different kinds of fluids, when the physical property data of a plurality of kinds of fluids are stored in a memory in advance and the flow rate rule of the fluids is used,
It may be possible to read the corresponding physical property data from the memory, but in the case of this measure, the measurable fluid is limited to the type selected in advance, and it is appropriate to meet the above demands. The reality was that he was not answered.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a thermal type flow meter capable of quickly and easily achieving an appropriate flow rate measurement according to the type of fluid.

[0006]

In order to achieve the above object, the present invention provides a heating element attached to a pipe through which a fluid passes, and an upstream side provided on the upstream side and the downstream side of the heating element of the tube. And a downstream-side temperature detecting means, and a heating means for calculating the flow rate of the fluid passing through the pipe based on the amount of heating of the fluid by the heating element and the temperature difference detected by the temperature detecting means. In the meter, the heat capacity is connected to at least one of the both temperature detecting means, and measures the heat capacity of the fluid based on the integrated heating amount for the fluid in the pipe in the stopped state and the temperature change obtained by the connected temperature detecting means. It is characterized by comprising a measuring means.

[0007]

With this structure, the heat capacity measuring means is
Since the heat capacity of the fluid is obtained based on the accumulated heating amount for the fluid in the pipe in the stopped state and the temperature change obtained by the temperature detecting means, it is accompanied by changing the fluid by measuring the flow rate using the physical property data of the arbitrary fluid. The flow rate of an arbitrary fluid can be measured according to the type of fluid without performing calibration for each part of the device.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A thermal type flow meter according to an embodiment of the present invention is shown in FIG.
Or, it demonstrates based on FIG. In the figure, reference numeral 1 denotes a pipe through which a fluid passes, and this pipe 1 is made of a thin metal material such as stainless steel or a resin material such as fluororesin.
A coil-shaped heater 2 is fitted in the middle of the tube 1 in a close contact state. A power supply circuit 3 is connected to the heater 2 and supplies power to the heater 2 to heat the heater 2.
The heat generated by the heater 2 heats the fluid. In this case, the power supply circuit 3 always heats the fluid in response to the measurement control signal a from the flow rate calculation circuit 4 described later, while inputting the change-time control signal b from the heat capacity measurement circuit 5 described later, The fluid heating by the measurement control signal a is interrupted, and the fluid is heated according to the change-time control signal b.

Upstream and downstream temperature sensors 6 and 7 are provided on the upstream and downstream portions of the heater 2 of the tube 1, respectively. Each of the upstream and downstream temperature sensors 6 and 7 is composed of a small thermistor, a thin film platinum resistance thermometer, or a thin wire made of metal such as platinum having a large temperature coefficient, and has excellent responsiveness. It has become.

An arithmetic means 8 is provided so as to be connected to the upstream and downstream temperature sensors 6, 7 and the power supply circuit 3.
Further, a heat capacity measuring circuit 5 is provided so as to be connected to the downstream temperature sensor 7.

The calculating means 8 is roughly composed of a temperature difference detecting circuit 9, the flow rate calculating circuit 4 and a physical property data changing circuit 10.

The temperature difference detection circuit 9 inputs the upstream and downstream detection temperatures T _a and T _b detected by the upstream and downstream temperature sensors 6 and 7, respectively, and receives a temperature difference ΔT (ΔT = T _b).
−T _a ), and this temperature difference ΔT is output to the flow rate calculation circuit 4.

The flow rate calculation circuit 4 serves as a reference (for calibration).
Specific heat C _P of the fluid S _f, determined by the heat capacity C _f, etc. of the fluid S _f, the relationship of the following equation (1) to the temperature difference ΔT and the like from the coefficient k _f and the temperature difference detecting circuit 9 as property data of the fluid S _f Based on the fact that there is, the equation (1) is calculated to obtain the mass flow rate Q. W = k _f · C _P · Q · ΔT (1) W: Heating amount for fluid

The physical property data changing circuit 10 receives the heat capacity C of the fluid S _{a to be} measured which is an arbitrary fluid from the heat capacity measuring circuit 5.
performs the following calculation (2) in accordance with the heat capacity C _a by inputting data indicating _a, obtains the coefficients k _a is the physical property data of the measurement target fluid S _a, the flow rate calculation of the flow rate operation circuit 4 The flow rate calculation circuit 4 is caused to use the coefficient k _a of the fluid to be measured S _a instead of the coefficient k _f used. k _a = C _a / C _f (2) C _f : Heat capacity of the calibration fluid S _f obtained in advance (however, C _f and C _a as the fluid to be measured are amounts corresponding to the heat capacity. , C _a = k · C (k: coefficient, C: heat capacity).)

The heat capacity measuring circuit 5 is connected to the switch 11, and when the switch 11 is turned on, the control signal b at the time of change is output to the power supply circuit 3 and the fluid S to be measured is to be described later. by performing measurement processing of _a heat capacity C _a, the heat capacity C _a obtained by the measurement process
Is output to the physical property data change circuit 10.

Fluid to be measured S _a by the heat capacity measuring circuit 5
The measurement process of the heat capacity C _a of will be described. First, the switch 11 is turned on to stop the operation of the power supply circuit 3 by the measurement-time control signal a, and in this state, the fluid S _a to be measured is sealed in the pipe 1 to keep the flow rate at zero. Next, heating of the fluid S _a to be measured is started with the heating amount W [cal / sec], and the temperature T _b = T _f after the time t _f seconds is measured.
Based on the above data, the heat capacity measuring circuit 5 calculates the following equation (3).
Is calculated to obtain the heat capacity C _a . C _a = W · t _f / (T _f −T ₀ ) ... (3) T ₀ : Temperature detected by the downstream temperature detection sensor 5 in the initial state

In the thermal type flow meter constructed as described above,
The fluid flowing in the pipe 1 is heated by the heater 2, and at that time, the upstream and downstream temperature sensors 6 and 7 perform temperature detection to detect the heating amount to the fluid, the temperature difference between the temperature detection sensors 6 and 7, and The flow rate (mass flow rate) of the fluid will be measured based on the physical property data of the fluid, but prior to the flow meter rule, the calibration fluid _f for which the specific heat C _P etc. has been clarified must be calibrated in advance for each part of the device. The specific data of the calibration fluid _f is set in the flow rate calculation circuit 4 and the like as well.

When measuring the flow rate of the fluid S _a to be measured, the temperature T _b = T ₀ of the downstream temperature detection sensor 5 is measured in advance at time t = 0 and the heating amount W = 0 (step S1, S2) At this stage, the switch 11 is turned on to start the time measurement, and the heater 2 is caused to generate heat to heat the fluid S _a to be measured at the heating amount W [cal / sec] to start the heat capacity measurement process. Yes (step S3).

The downstream temperature detecting sensor 7 outputs the detected temperature T _b to the heat capacity measuring circuit 5 (step S4), while the heat capacity measuring circuit 5 makes the time t from step S3 equal to the time t _f. By inputting the detected temperature T _f of the downstream side temperature detection sensor 7 in step S5, S6, the calculation of the equation (3) is performed to obtain the heat capacity C _a , and the heat capacity C _a is changed to the physical property data. Output to circuit 10 (step
S7).

The physical property data change circuit 10 inputs the heat capacity C _a to carry out the calculation of the equation (2) to obtain the coefficient k.
_a is obtained (step S8), this coefficient k _a is output to the flow rate calculation circuit 4, and this coefficient k _a is replaced with the coefficient k of the equation (1) used for flow rate calculation in the flow rate calculation circuit 4 ( At step S9), the switch 11 is turned off by the end of this process, and the operation of the power supply circuit 3 by the change-time control signal b is stopped.

At the stage where the above process is completed, the fluid S _a to be measured is flown into the pipe 1, and the fluid S to be measured flowing in the pipe 1 is flown.
_A is heated by the heater 2, and at that time, the temperature is detected by the upstream and downstream temperature sensors 6 and 7, and the measurement target fluid S
_Based on the heating amount W to _a , the temperature difference ΔT detected by both temperature detection sensors 6 and 7 and the coefficient ka changed in step S9, the calculation of (1) is performed to determine the flow rate (mass flow rate) of the fluid S _a to be measured. ) Get Q.

When measuring the flow rate of another type of fluid, a new measurement is performed by performing the above-described process shown in FIG. 3 on the fluid to be newly measured in the same manner as described above. The flow rate of the target fluid can be measured with high accuracy.

[0023] Thus determined the heat capacity C _a heat capacity measuring circuit 5 is measured fluid S _a, the coefficient k _a measurement target fluid S _a on the basis of the heat capacity measurement circuit 5 in the heat capacity C _a measurement target fluid S _a Since the coefficient k _a of the fluid S _{a to be} measured is used instead of the coefficient k _f of the predetermined fluid S _f which is obtained and used in the flow rate calculation circuit 4, it is possible to change each part of the apparatus accompanying the change of the fluid. The flow rate of the measurement target fluid S _a can be measured without performing calibration for each fluid. Since it is not necessary to calibrate each part of the device, flow rate measurement of many kinds of fluids can be easily performed in a short time. Further, in the conventional thermal type flow meter in which the physical property data of the fluid and the like are stored in the memory and the flow rate of the fluid is measured, the types of measurable fluid are limited to those in which the data is stored in advance in the memory. On the other hand, the thermal type flow meter of the present invention can measure the flow rate of the fluid over many types.

Although the heat capacity measuring circuit 5 is connected to the downstream temperature detecting sensor 7 in the above embodiment, the present invention is not limited to this.
It may be provided so as to be connected to the upstream side temperature detection sensor 6, or may be provided so as to be connected to the upstream side and downstream side temperature detection sensors 6 and 7 so as to use an average value, for example.

[0025]

Since the present invention is the thermal type flow meter configured as described above, the flow rate of the fluid to be measured can be adjusted according to the type of the fluid without performing calibration for each part of the device for each fluid. Since it is possible to measure, it is possible to easily measure the flow rates of various kinds of fluids in a short time. In addition, since the flow rate can be measured according to the type of fluid, the flow rate of the fluid can be measured over many types.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a thermal type flow meter according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a circuit portion of the same thermal type flow meter.

FIG. 3 is a flowchart showing the operation of the same thermal type flow meter.

[Explanation of symbols]

1 tube 2 heater 4 flow rate calculation circuit 5 heat capacity measurement circuit 6 upstream temperature sensor 7 downstream temperature sensor 8 calculation means 10 physical property data change circuit W heating amount for fluid ΔT detection temperature difference S _f predetermined fluid S _a measurement target fluid (arbitrary fluid) property data of k _f factor (physical data of a predetermined fluid) k _a coefficient (any fluid) Q _a any fluid heat capacity

Claims (1)

[Claims] 1. A heating element attached to a pipe through which a fluid passes, upstream and downstream temperature detecting means respectively provided on the upstream side and the downstream side of the heating element of the pipe, and the heating element to the fluid. In a thermal type flow meter having a heating amount and a calculating means for obtaining the flow rate of the fluid passing through the pipe based on the temperature difference detected by the both temperature detecting means, the thermal type flow meter is connected to at least one of the both temperature detecting means, Further, the thermal type flow meter is provided with a heat capacity measuring means for measuring a heat capacity of the fluid based on a temperature change obtained by the integrated heating amount and the connected temperature detecting means in the stopped state.