JPS59105520A - Thermal type mass flowmeter - Google Patents

Abstract

PURPOSE:To enable a highly accurate measurement by mounting a closed end plate at both ends of an outer cylinder made of a highly heat conductive material provided around a heater mounted section in a passage pipe. CONSTITUTION:The outside of a heater 2 of a flowmeter is covered with a heat insulator 5. A highly heat conductive outer cylinder 7 is provided on the upstream and downstream sides of a passage to cover the insulator and the outside thereof is covered with a heat insulator 8. End plates 6 and 6' as good heat conductor and the outer cylinder 7 are allowed to maintain the temperatures at the upstream and downstream sides of the heater 2 at the same level. Therefore, according to this invention, changes in the temperatures at the upstream and downstream sides of a sensor and the ambient temperature are prevented to eliminate effect of temperature difference completely at two points in the direction of flow of the sensor generating a flow rate signal thereby enabling a highly accurate measurement of flow rate.

Description

DETAILED DESCRIPTION OF THE INVENTION In a device as shown in FIG.
When fluid flows through an electrically heated channel, a certain relationship is established between the temperature difference 4T between two points A and B in the flow direction of the channel and the flow rate flowing through the channel. Flowmeters equipped with sensors that utilize this principle are in practical use mainly as flowmeters that measure the flow rate of gas.

Incidentally, the measurement accuracy and stability of indications of this type of flowmeter are related to problems in the structure and configuration of the sensor.

The first is the temperature difference between points A and B, which is detected as a flow rate signal.
has a relationship with the temperature at point 0 on the upstream side and point D on the downstream side, and in order to perform accurate measurement, it is necessary to keep the temperatures at point 0 and point D constant.

Second, in order to prevent heat from being released from the sensor to the surroundings, the sensor is covered with an insulating material, but this cannot be completely prevented, and the heat loss through this insulating material is detected as a flow signal. This affects the temperature difference between points A and B.

On the other hand, the amount of heat loss through the insulation is related to the ambient temperature of the sensor. That is, in order to ensure high measurement accuracy even when the ambient temperature changes, it is necessary to keep the amount of heat loss through the heat insulating material constant.

The present invention takes the above points into consideration and provides a flowmeter sensor that can ensure high measurement accuracy under a wide range of usage conditions.

FIG. 2 shows a specific embodiment of the present invention.

In the figure, numeral 1 is a pipe for a flow path through which fluid flows, 2 is a heater made of a heating wire for heating the flow path,
3 is a power source that supplies power to heater 2, 4 and 4I are thermocouple wires connected to detect the temperature difference between two points A and H on the wall of the pipe, 4A is a meter such as an ammeter, and 7 is a The outer cylinders 6 and 61 are made of a thermally conductive material made of a metal with high thermal conductivity such as copper or aluminum, and the central hole is fitted into the pipe, and the outer cylinder is made of a thermally conductive material as well. 5 indicates a heat insulating material provided inside the outer tube 7, and 8 indicates a heat insulating material provided outside the outer tube 7.

The flow rate measurement principle of such a device will be explained as follows. The pipe 1 is heated by a heater 2 to which power is supplied from a power source 3.

Thermocouples 4 and 4 measure the temperature difference between two points in the flow direction on the pipe wall of flow path 1.
1, there is a certain relationship between this temperature difference and the flow rate, so the flow rate can be determined from the output of the thermocouple.

By the way, in the present invention, the outside of the heater 2 is covered with a heat insulating material 5, and around it are heat conductive end plates 6, 6I provided on the upstream and downstream sides of the flow path, and heat conductive end plates 6, 6I that are also connected to the heat conductive end plates 6, 6I, and Since the end plates 6 and 61 and the outer cylinder 7, which are good conductors of heat, maintain the same temperature on the upstream and downstream sides of the heater 2, Keep at temperature.

Therefore, the temperature difference detected by the thermocouples 4 and 41 is completely unaffected by the temperatures on the upstream and downstream sides of the sensor.

The heat insulating material 5 insulates the space between the heater 2 and the outer cylinder 7 to prevent heat loss from the heater 2 to the outer cylinder 7. The heat insulating material 8 insulates the space between the surrounding gas and the outer cylinder 7, and even if the ambient temperature changes, the outer cylinder 7
The temperature of the end plates 6, 61 is maintained at the same temperature as that of the end plates 6, 61. Therefore, heat loss from the heater 2 to the outer cylinder 7 through the heat insulating material 5 is kept constant even if the ambient temperature changes.
The temperature difference detected by the thermocouples 4 and 41 is not affected by the ambient temperature at all.

As described above, according to the present invention, changes in the temperature on the upstream side and downstream side of the sensor, as well as the ambient temperature, are completely unaffected by the temperature difference between two points in the flow direction of the sensor, which is a flow rate signal. Accurate flow measurement is possible even under a variety of conditions.

Note that the outer heat insulating material layer 8 may be formed not only on the outer surface of the outer cylinder 7 but also on the outer surfaces of the end plates 6 and 61.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a thermal mass flowmeter, and FIG. 2 is a diagram showing a thermal mass flowmeter according to the present invention. In the diagram: 1 Flow path pipe 2 Heater 3 Power supply 4, 4I thermocouple 4A meter 5 Insulation material 6.61 End plate 7 Outer tube 8 Insulation layer Applicant Tokyo Keiso Co., Ltd. Agent Patent attorney Mae 1) Kiyomi

Claims (1)

[Claims] In a flowmeter, a heater is attached to a part of the outside of the flow path pipe, and the flow rate is measured by detecting the temperature difference between two points in the axial direction of the flow path pipe at the heater attachment part using a thermocouple. An outer cylinder made of a thermally conductive material is provided around the heater attachment part of the flow path pipe, and a center hole of the same thermally conductive material is provided at both ends of the outer cylinder, and a central hole is fitted into the flow path pipe. Attach a closed end plate consisting of
A thermal mass flow needle, characterized in that a heat insulating material layer is formed on the outer surface of the needle, and a heat insulating material is provided inside to block heat conduction between the heater, the outer cylinder, and the end plate.