Strain detector having water-protective layer

Details Strain detector having water-protective layer Strain detector having water-protective layer

2000-12-28

2004-07-13

Noori, Max (Department: 2855)

Measuring and testing

Specimen stress or strain, or testing by stress or strain...

Specified electrical sensor or system

C073S777000

Reexamination Certificate

active

06761073

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a strain detector for detecting a strain resulting from a load.
BACKGROUND OF THE INVENTION
Japanese Patent Laid Open Publication No. 8-87375 discloses a conventional strain detector. The conventional strain detector will be described with reference to drawings hereinafter.
FIG. 8
is a top view of the conventional strain detector, and
FIG. 9
is a cross sectional side view of the detector.
In FIG.
8
and
FIG. 9
, insulating substrate
1
made of elastic material is formed by disposing stick member
2
and insulating layer
3
thereon. Four strain-resistance elements
4
are disposed over insulating substrate
1
. Strain-resistance elements
4
are electrically coupled to a pair of power electrodes
5
, a pair of output electrodes
6
, and a pair of ground (GND) electrodes
7
to form a bridge circuit. Protective layer
8
made of resins covers elements
4
, power electrodes
5
, the pair of output electrodes
6
, the pair of GND electrodes
7
and the rest of insulating substrate
1
.
The operation of the above conventional strain detector will be described hereinafter.
When a shearing load is applied on the general-center position of the top of insulating substrate
1
, a bending moment occurs in insulating substrate
1
via the shearing load and also occurs in the four strain-resistance elements
4
disposed over substrate
1
. A resistance of strain-resistance elements
4
changes by the bending moment resulting in elements
4
. A change of the resistance is supplied from the pair of output electrodes
6
to an external measuring device (not shown), and then the load on substrate
1
is measured.
In the conventional strain detector, only protective layer
8
made of resins is disposed over insulating substrate
1
, the pair of power electrodes
5
, the pair of output electrodes
6
and the pair of GND electrodes
7
. Protective layer
8
made of resins absorbs water little by little. Therefore, when the strain detector is used for a long time in an atmosphere of high humidity, the water reaches strain-resistance elements
4
and the resistance of strain-resistance elements
4
fluctuates.
SUMMARY OF THE INVENTION
The present invention provides a strain detector, where water does not reach strain-resistance elements, such that stable output properties are at all times exhibited.
The strain detector comprises:
(a) An insulating substrate made of elastic materials;
(b) Four strain-resistance elements, which form a bridge circuit by being electrically coupled to a power electrode, a pair of output electrodes, and a ground (GND) electrode, disposed over the insulating substrate;
(c) A temperature-characteristic-compensation element disposed over the insulating substrate; and
(d) A first protective layer for covering the insulating substrate, the strain-resistance elements, the power electrode, the pair of output electrodes, the GND electrode and a temperature-characteristic-compensating element.


REFERENCES:
patent: 4771638 (1988-09-01), Sugiyama et al.
patent: 4945770 (1990-08-01), Alvelid et al.
patent: 5393351 (1995-02-01), Kinard et al.
patent: 8-87375 (1996-04-01), None
patent: 2000-180255 (2000-06-01), None

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