Measuring and testing – Volume or rate of flow – Thermal type
Reexamination Certificate
2003-02-26
2004-10-05
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Volume or rate of flow
Thermal type
Reexamination Certificate
active
06799456
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermal flow sensor for measuring a flow rate by means of hot wires.
2. Description of Related Art
Some conventional thermal flow sensors for measuring a flow rate by using hot wires are provided with a measuring chip manufactured by a semiconductor micro-machining technology as a sensor part as shown in FIG.
18
. In a thermal flow sensor
101
in
FIG. 18
, a gas to be measured is caused to flow in an inlet port
102
, is made into a laminar flow by a laminar flow mechanism
103
, and is caused to pass through a measuring passage
104
and flow out through an outlet port
105
. For measurements of the flow rate of the gas, a measuring chip
111
connected to an electric circuit
106
is arranged in an exposed state in the measuring passage
104
.
In this regard, the measuring chip
111
is constructed, as shown in
FIG. 19
, of a silicon chip
116
on which an upstream thermo-sensor
112
, a heater
113
, a downstream thermo-sensor
114
, and an ambient temperature sensor
115
(these sensors
112
through
115
correspond to “hot wires”) and others are formed by a semiconductor micro-machining technology.
Accordingly, in the thermal flow sensor
101
in
FIG. 18
, while the gas does not flow through the measuring passage
104
, the distribution of temperatures of the measuring chip
111
in
FIG. 19
is symmetrical with respect to the heater
113
. While the gas flows through the measuring passage
104
, on the other hand, the temperature of the upstream thermo-sensor
112
is decreased and the temperature of the downstream thermo-sensor
114
is increased. Accordingly, the distribution of temperatures of the measuring chip
111
becomes unsymmetrical according to the flow rate of the gas to be measured. At this time, the degree of such unsymmetry is outputted as a difference in resistance values between the upstream thermo-sensor
112
and the downstream thermo-sensor
114
. Thus, the flow rate of the gas can be measured by the electric circuit
106
.
In the thermal flow sensor
101
in
FIG. 18
, however, six electrodes D
1
, D
2
, D
3
, D
4
, D
5
, and D
6
are provided on the silicon chip
116
of the measuring chip
111
in
FIG. 19
so that the upstream thermo-sensor
112
, the heater
113
, the downstream thermo-sensor
114
, and the ambient temp. sensor
115
are individually connected to the electric circuit
106
by wire bonding using those six electrodes D
1
-D
6
.
In the thermal flow sensor
101
in
FIG. 18
as above, the measuring chip
111
is exposed in the inside of the measuring passage
104
where a bonding wire W is provided. When a high flow rate of a gas to be measured is caused to flow in the measuring passage
104
, accordingly, the bonding wire W can possibly be cut due to the pressure of the flowing gas. To prevent it, addition of a covering mechanism (for example, “a support body
13
a
” in Japanese patent unexamined publication No. Hei 10-2773) or other measures must be taken.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a thermal flow sensor which uses a measuring chip as a sensor part, the measuring chip being provided with hot wires, and which can eliminate the use of wire bonding for connection between the hot wires of the measuring chip and an electric circuit.
The thermal flow sensor according to the present invention made to achieve the above purpose is characterized by including: a measuring chip provided with a hot wire and an electrode for the hot wire, the electrode being connected to the hot wire; a board having a front side on which an electrode for an electric circuit is provided, the electrode being connected to the electric circuit for performing a measuring principle using the hot wire; a body to which the measuring chip is attached in close contact relation to form a main passage; wherein at least one of the measuring chip and the board is formed with a groove, and a sensor passage in relation to the main passage is formed by the groove between the measuring chip and the board in a state where the measuring chip is mounted on the board with the hot wire electrode being joined to the electric circuit electrode, and the hot wire is laid across the sensor passage.
The thermal flow sensor according to another aspect of the invention is characterized a thermal flow sensor including: a measuring chip provided with a hot wire and an electrode for the hot wire, the electrode being connected to the hot wire; an electric circuit electrode pin connected to an electric circuit for performing a measuring principle using the hot wire; a board in which the electrode pin is inserted; an elastic body which provides a seal between the electric circuit electrode pin and the board; and a body in which the board is attached in close contact relation to form a main passage; wherein a sensor passage in relation to the main passage is formed in a long slot shape by a thickness of the elastic body between the measuring chip and the board in a state where the measuring chip is mounted on a front side of the board with the hot wire electrode being joined to a flat head of the electric circuit electrode pin, and the hot wire is laid across the sensor passage.
REFERENCES:
patent: 4542650 (1985-09-01), Renken et al.
patent: 5595163 (1997-01-01), Nogi et al.
patent: 5914019 (1999-06-01), Dodgson et al.
patent: 6035712 (2000-03-01), Ohta et al.
patent: A 10-2773 (1998-01-01), None
Ito Akihiro
Kawai Yoshihiko
CKD Corporation
Lefkowitz Edward
Oliff & Berridg,e PLC
Thompson Jewel V.
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