Sensed-pressure-data converter

Details Sensed-pressure-data converter Sensed-pressure-data converter

2001-04-03

2003-01-14

Oda, Christine (Department: 2858)

Electricity: measuring and testing

Impedance, admittance or other quantities representative of...

Piezoelectric crystal testing

C702S098000

Reexamination Certificate

active

06507202

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a sensed-pressure-data converter having a circuit for reducing an output offset and an offset drift of a pressure sensitive resistance element.
BACKGROUND ART
Today, pressure sensitive resistance elements are widely used as various pressure sensors and keyboard switches.
FIG. 14
is an explanatory diagram showing a conventional pressure sensitive resistance element. In
FIG. 14
, reference numeral
51
denotes an upper film as an insulating substrate, reference numeral
52
denotes a lower film also as an insulating substrate, reference numeral
53
denotes an Ag electrode pattern formed on lower film
52
, reference numeral
54
denotes an Ag electrode pattern formed on upper film
51
oppositely to Ag electrode patterns
53
, and reference numeral
55
denotes a pressure sensitive conductor applied and formed on the Ag electrode pattern
54
. Lower film
52
and upper film
51
are disposed so that pressure sensitive conductor
55
may contact with Ag electrode pattern
53
. This pressure sensitive conductor
55
is formed by mixing conductive particles in an insulating rubber material. Pressing and, compressing pressure sensitive conductor
55
makes gaps of the conductive particles in pressure sensitive conductor
55
narrower and the resistance lower. That is, as the pressure getting high, the resistance falls. In the conventional sensed-pressure-data converter, this resistance change is directly converted into a voltage.
In such conventional pressure sensitive resistance element, in general, the pressure sensitive conductor is formed by printing method in order to reduce cost, and therefore, the resistance and resistance changing characteristic vary depending on the thickness of the pressure sensitive conductor. Consequently, it was difficult to maintain the resistance at a desired value and keep fluctuations of the changing characteristic within a specific range. It was hence difficult to obtain a desired output if the resistance value of the pressure sensitive resistance element is directly converted into a voltage.
SUMMARY OF THE INVENTION
The invention is intended to solve these problems, and it is hence an object thereof to present a sensed-pressure-data converter having a circuit for reducing an output offset and an offset drift of a pressure sensitive resistance element.
To solve the problems, the sensed-pressure-data converter of the invention comprises:
a pressure sensitive resistance element having a pressure sensitive conductor interposed between two insulating substrates disposed face to face, for varying the resistance thereof corresponding to the load applied from outside within the confronting surfaces of the insulating substrates; and
controller for detecting the electric characteristic of the pressure sensitive resistance element, for converting it to a specific electric characteristic signal and for issuing it.
The controller comprises:
an A/D converter receiving a signal from the pressure sensitive resistance element;
a memory preliminarily storing a compensation value based on an error signal between the electric characteristic of the pressure sensitive resistance element and the reference electric characteristic;
a D/A converter for compensating the electric characteristic due to the resistance change of the pressure sensitive resistance element as compared with the signal from the A/D converter based on the compensation value stored in the memory, for converting it into a specific electric characteristic signal, and for issuing it; and
an adjustment value input terminal for entering the error signal into the input terminal of the A/D converter.
In this constitution, a sensed-pressure-data converter capable of reducing the output offset and the offset drift of the pressure sensitive resistance element is obtained.


REFERENCES:
patent: 4399515 (1983-08-01), Gross
patent: 5146788 (1992-09-01), Raynes
patent: 5479096 (1995-12-01), Szczyrbak et al.
patent: 63-290922 (1988-11-01), None
patent: 5-45520 (1993-06-01), None
patent: 6-265425 (1994-09-01), None
patent: 9-061276 (1997-03-01), None
patent: 11-083420 (1999-03-01), None

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