JPH03195924A - Method and apparatus for measuring flow rate of liquid - Google Patents

Abstract

PURPOSE:To determine the velocity of a liquid flow in a conduit by changing a temperature at a prescribed spot outside the conduit through which a liquid flows and by measuring a delay of a change in the temperature at a prescribed spot located on the downstream side of the former. CONSTITUTION:A heater 2 connected to a power source 3 is provided on a conduit 1 through which a liquid flows, and a temperature measuring element 4 connected to a detecting circuit 5 is provided on the downstream side of the heater 2. A change in temperature is detected by the temperature measuring element 4 and a signal thereof enters an arithmetic circuit 7. Meanwhile, a signal from an oscillator 6 also enters the arithmetic circuit 7, a time delay T of the change in temperature is determined therein and the velocity of the liquid is calculated with correction at the time of a low velocity included. Now, when a spot whereat the change in temperature is given is set at a point A and a spot whereat the change in temperature is measured is set at a point B, the quantity of generated heat or the quantity of absorbed heat as to the change in temperature given at the point A can be made small, since the points A and B can be set in proximity to each other. Accordingly, it does not happen that the temperature of a heating part turns so high as to boil or cause pyrolysis, or that the temperature of a heat absorbing part turns so low as to be hardened or cause an increase in viscosity.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for measuring the flow rate of a liquid flowing in a conduit and to an apparatus for carrying out the method.

(Prior Art) Conventionally, thermal mass flowmeters have been mainly used to precisely measure minute amounts of flow in semiconductor manufacturing processes and the like.

This flowmeter has temperature-sensitive resistance wire wrapped around two locations on the outside of the conduit.
A heater wire is wound between these two points and a constant current is passed through them to heat them. When liquid flows through this conduit, the temperature decreases upstream and increases downstream, creating a temperature difference between the two locations.

Also, endotherm may be used instead of exotherm.

That is, instead of a heater wire, a Peltier element is used to flow a constant current for cooling. When a liquid flows through this conduit, the temperature increases at the upstream portion and decreases at the downstream portion, creating a temperature difference between the two locations.

The rate at which this temperature difference changes is determined by the size of the heat capacity of the liquid. From this, the flow of liquid is converted into a change in temperature difference as a mass flow rate, and this change is detected by a bridge circuit as a change in the resistance value of the temperature-sensitive resistance wire.

As mentioned above, conventional mass flowmeters are based on steady-state measurement due to heat generation or heat absorption, so when the flow of liquid stops, the heat generating part becomes too high and may boil or cause thermal decomposition. There are disadvantages, such as the heat absorption part becoming too cold and solidifying or increasing viscosity.

Furthermore, if the amount of heat generated or the amount of heat absorbed is limited, there is a drawback that the measurement speed decreases.

Furthermore, since it is necessary to wait until the signal is in a steady state, the measurement time becomes long and measurement accuracy cannot be improved.

Additionally, this mass flow meter has the disadvantage that it requires correction based on the heat capacity, viscosity, etc. of the liquid.

(Problems to be Solved) The present invention aims to eliminate the above-mentioned drawbacks and provide a measurement method that can accurately and quickly measure a minute flow rate of a liquid, and an apparatus for implementing the method. It is.

(Means for Solving the Problem) The present invention changes the temperature of a fixed point outside the conduit through which the liquid flows, and measures the delay in temperature change at a fixed point downstream thereof, thereby increasing the velocity of the liquid flow inside the pipe. This is the way to find out.

Now, if we change the temperature at a certain point outside the conduit,
Because there is heat conduction through the conduit, and heat conduction through the liquid if there is stationary liquid in the conduit, a signal is generated even when no liquid is flowing.

When a liquid flows through this conduit, the temperature change at a certain point is transferred by the liquid flow. When this liquid flow is sufficiently faster than the heat conduction rate in a stationary state, the following formula % formula % where L is the distance between the temperature change point and the temperature measurement point, T
is the time delay of temperature change, and ■ is the average flow velocity.

When L is kept constant, the average flow velocity V and the temperature change time delay T are inversely proportional.

Now, let the point where the temperature change is applied be point A, and the point where the temperature change is measured be point B.

When there is no flow of liquid in the conduit, the waveform of temperature change that oscillates at point A reaches point B due to heat conduction through the conduit and the stationary liquid and is detected by the temperature sensor, so the time of temperature change is The value of the delay T is large.

Next, when the liquid flows in the conduit, the waveform of the temperature change that oscillates at point A changes to B due to the addition of heat transport due to the liquid flow.
It is transmitted quickly to the point, and the value of the time delay T of temperature change becomes small.

As explained above, the average flow velocity V can be determined by measuring the time delay T of temperature change.

The time delay T in temperature change can be measured using a signal from a temperature measuring element that detects a temperature change and a signal from an oscillator.

As the element for changing the temperature, a heater can be used in the case of heat generation, and a Peltier element can be used in the case of heat absorption.

A temperature sensing element such as a thermistor can be used as the temperature measuring element.

Since the heat conduction rate when the liquid flow is in a stationary state is generally slow, the distance between points A and B is shortened, and it is sufficient that the measurement period is slightly longer than the delay time of temperature change in a stationary state.

Time can be measured with extremely high precision, and change signals can be measured more easily and stably than absolute value measurement, resulting in higher measurement accuracy.

Furthermore, since there is no need for complete thermal insulation between points A and B, the measurement time becomes faster.

Next, an apparatus for carrying out the method according to the present invention will be described.

FIG. 1 is a block diagram of an apparatus according to the present invention.

A heater 2 connected to a power source 3 is installed in the conduit 1 through which the liquid flows, and this heater 2 provides a temperature change. A temperature measuring element 4 connected to a detection circuit 5 is installed downstream of the heater 2, and a temperature change is detected by the temperature measuring element 4, and the signal is input to an arithmetic circuit 7. On the other hand, oscillator 6
The signal from the liquid flow rate is also input to the arithmetic circuit 7, where the time delay T of temperature change is determined, and the flow rate is calculated including correction for low flow rate of liquid.

(Effects of the Invention) According to the present invention, since the temperature change given at point A can be made close to point A and B, the amount of heat generated or absorbed can be reduced, so the heat generating part becomes too high temperature and boils. It has the characteristic that it does not cause heat decomposition or thermal decomposition, and does not solidify or increase viscosity due to the temperature of the heat absorbing part becoming too low.

Furthermore, since the present invention uses only thermal changes without utilizing thermal equilibrium, the measurement time is extremely fast and the measurement accuracy is high.

Another advantage is that it does not require correction based on the heat capacity, viscosity, etc. of the liquid.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a liquid flow rate measuring device according to the present invention. In the figure, 1 is a conduit through which liquid flows, 2 is a heater, and 3
is a power supply, 4 is a temperature measuring element, 5 is a detection circuit, 6 is an oscillator, 7
8 is a calculation circuit, and 8 is a flow rate display section.

Claims (2)

[Claims] (1) Measurement of liquid flow rate, characterized by determining the velocity of the liquid flow in the pipe by changing the temperature at a fixed point outside the pipe through which the liquid flows and measuring the delay in temperature change at a fixed point downstream of the change in temperature. Law. (2) A heat generating element or a heat absorbing element connected to a power source is installed in the upstream part of the conduit through which the liquid flows, a temperature measuring element connected to a detection circuit is installed in the downstream part of the conduit, and an oscillator is installed in the circuit. 1. A liquid flow rate measuring device, which is installed in a pipe and measures the delay in temperature change between an upstream portion and a downstream portion, thereby determining the velocity of a liquid flow within a pipe.