JPS6126824A - Thermal type flow rate detecting sensor - Google Patents

Abstract

PURPOSE:To improve the responsibility of the sensor and reduce variance in time constant by forming trimming grooves in an insulating pipe lengthwise. CONSTITUTION:A temperature dependent resistance film 2 is vapor-deposited on the external surface of the cemamic-made cylindrical insulating pipe 1. Then, platinum wires 3 are inserted into said insulating pipe from both end opening parts and platimum paste 4 is stuck and sintered to fix the wires. Further, the trimming grooves 5 are formed in the platinum thin film 2 alternately in a comb shape up to positions about 0.1mm. way from both ends in the lengthwise direction of the sensor by using a laser trimmer. Thus, the trimming grooves 5 are provided to the insulating pipe 1 lengthwise, so the insulating pipe 1 is easily trimmed almost to both end parts, so superior responsibility is obtained while the sensitivity and accuracy of the sensor are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a heat-sensitive flow rate detection sensor that detects a flow rate using heat transfer between a temperature-dependent resistive film and a fluid.

[Prior art]

A conventional heat-sensitive flow rate detection sensor is shown in FIG. In the figure, (1) is a cylindrical insulating tube made of ceramic or quartz, etc., (2) is a temperature-dependent resistive film formed on the outer surface of this insulating tube (1), in this case a platinum resistive film, and (3) is a platinum resistive film. (4) is a platinum paste for connecting this lead (3) and the insulating tube (1), (5) is a heat-sensitive flow rate. The trimming groove is formed in a spiral shape using a laser so that the resistance value of the detection cell becomes a desired value, and is created so that no temperature-dependent resistance film remains in the groove portion. (6) is a coating film made of Al2O or 5i02 provided on the platinum resistive film (2) and the trimming groove (5).

The heat-sensitive flow rate detection sensor formed as described above is energized and heated to a temperature higher than the fluid temperature. It is generally known that when a fluid hits this, the flow rate and amount of heat corresponding to the flow rate are taken away from the sensor, and the following King's relational expression holds between the flow rate Q and the heat ti+ at that time.

H= (A+Br, ) (TH-Ta), so A,
B is a constant and TH-Th is the temperature difference between the sensor and the fluid. Therefore, the flow rate or flow velocity can be measured by keeping the temperature difference constant and detecting the amount of heat H or the heating current corresponding to it.

As shown in Figure 1, conventional heat-sensitive flow rate detection sensors have trimming grooves formed in a spiral shape, so the structure tends to leave parts without trimming grooves at both ends or one end of the insulation tube. It had the following drawbacks. In other words, since the part that generates heat due to the heating current is the central part of the sensor where the trimming groove is provided, the sensitivity to changes in flow rate is low at both ends of the sensor, and the response of the sensor is affected by the heat capacity of that part. It had the disadvantage of being late.

Conventional heat-sensitive flow rate detection sensors are trimmed in a spiral shape as described above, so depending on the resistance value, a portion without the trimming groove may remain near the end of the sensor, resulting in poor response and time constant variation depending on the sensor. There was a drawback.

[Summary of the invention]

This invention was made to eliminate the above-mentioned drawbacks of the conventional method, and by creating trimming grooves along the longitudinal direction of the insulating tube, it has excellent responsiveness and small variation in time constant. The present invention provides a heat-sensitive flow rate detection device.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. Second
In the figure, (1) has an outer diameter of 1 mm, an inner diameter of 0.6 mm, and a length of 3 mm.
．． A cylindrical ceramic insulating tube (2) with a thickness of approximately 20 mm is formed by vapor deposition on the outer surface of the insulating tube (1).
Temperature-dependent resistance film made of platinum thin film of 0 (3)
For example, a platinum wire with a diameter of 0.3 tan is inserted through the openings at both ends of the insulating tube (1), and a platinum paste (4) is attached and sintered to fix it. (5) Approximately 0.0 mm is applied to the platinum thin film (2) from both ends in the longitudinal direction of the sensor using a laser trimmer.
1. Trimming grooves alternately provided in a comb shape up to the dark area,
Laser/J is applied so that the platinum thin film does not remain in the groove.
11 steps are performed to form the sensor to have a desired resistance value. (6) is a coating film of amorphous glass coated on the platinum thin film (2).

The above-mentioned senna is arranged so that its longitudinal direction is approximately perpendicular or parallel to the flow direction of the fluid, and its operating method is the same as that of conventional devices, so it will not be explained here. omitted.

In the heat-sensitive flow rate detection sensor configured as described above, the trimming groove is provided close to both ends of the sensor, so the resistance value for a unit length in the central axis direction is completely uniform between the lead terminals. 't' indicates the distribution.

Therefore, when electricity is applied, the heat generation distribution on the surface of the platinum thin film exhibits a uniform distribution in the longitudinal direction up to the lead terminals.

This increases the sensitivity to changes in flow velocity near both ends of the insulating tube and increases the effective heat transfer area.

Next, the transient characteristics of the sensor will be explained.

Figures 1 and 2 show changes in heating current over time in response to sudden changes in flow rate during constant temperature difference operation.

In the figure, A is the characteristic of a conventional sensor, and B is a characteristic of an embodiment of the present invention.

In conventional sensors, heat transfer to the fluid occurs not only from the heat generating part in the center of the senna directly to the fluid, but also through non-heat generating parts where trimming grooves have not been installed, resulting in a time delay. However, in the above example, almost all of the calorific value is transmitted directly to the fluid, so the response characteristics are so excellent that the time delay corresponding to the heat capacity of the senna, which was seen in conventional sensors, can be ignored. can now be obtained.

Next, the relationship between the ratio of the longitudinal length of the trimming groove to the length of the insulating tube, that is, the trimming rate, and the time constant when measured by the constant temperature difference method is shown in Figure 4. The larger the time constant, the smaller the time constant, and the trimming rate 9
It changes almost linearly up to around 0%. Therefore, by setting the trimming rate of the temperature sensing element to 90% or more, a thermal flow rate detection sensor with excellent responsiveness can be realized.

In the above embodiment, a platinum thin film was formed on the outer surface of the insulating tube by vapor deposition, but a paste containing platinum powder may also be applied.

Further, in the above embodiment, the trimming grooves were provided in a comb shape on the platinum thin film, but the same effect can be achieved by providing them in a zigzag shape in the longitudinal direction of the sensor.

〔Effect of the invention〕

As described above, according to the present invention, since the trimming groove is provided along the longitudinal direction of the insulating tube, it becomes easier to trim the insulating tube to the vicinity of both ends, which increases the sensitivity and accuracy of the sensor, and at the same time improves the response. It has the effect of producing excellent products.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing a conventional heat-sensitive flow rate detection sensor;
FIG. 2 is a perspective view showing a heat-sensitive flow rate detection sensor according to an embodiment of the present invention, FIG. FIG. 4 is a characteristic diagram showing the relationship between the trimming groove and the time constant of a heat-sensitive flow rate detection sensor according to an embodiment of the present invention. (1)...Insulating tube, (2)...Temperature-dependent resistance film,
(5) Trimming groove. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (2)

[Claims] (1) Forming a temperature-dependent resistance film on the outer surface of the insulating tube,
A trimming groove is formed in the temperature-dependent resistive film by laser processing so that the temperature-dependent resistive film does not remain in the groove portion, and is formed to have a desired resistance value, and the trimming groove is formed in the insulating film. A heat-sensitive flow rate detection sensor characterized by being created along the longitudinal direction of a pipe. (2) Claim 1 characterized in that the length of the trimming groove in the longitudinal direction is 90% or more of the length of the insulating tube.
Heat-sensitive flow rate detection sensor as described in .