Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – With auxiliary means to condition stimulus/response signals
Reexamination Certificate
2000-08-28
2003-02-11
Oda, Christine (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
With auxiliary means to condition stimulus/response signals
C073S335020
Reexamination Certificate
active
06518773
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a sensor sensitivity adjusting apparatus.
There are two conventional methods of adjusting the sensitivity of a sensor device: one using constant-current driving and the other using constant-voltage driving. The constant-current drive system controls the sensitivity of a sensor by adjusting the current that flows through the sensor. The constant-voltage drive system controls the sensor sensitivity by adjusting the voltage that is applied to the sensor.
FIG. 1
is a schematic block diagram of a conventional sensor sensitivity adjusting apparatus which adjusts the sensitivity of a sensor based on the constant-current drive system. A fixed resistor R
11
and a variable resistor R
12
divide the supply voltage to produce a reference voltage V
1
. The reference voltage V
1
is applied to the plus terminal of an operational amplifier
12
. The current I
1
that flows in a sensor
11
is controlled by adjusting the resistance of the variable resistor R
12
. The current I
1
that flows in the sensor
11
is defined by a fixed resistor R
13
, which has a stable temperature characteristic.
A detection signal from the sensor
11
is amplified by an amplifier circuit
13
, and the amplified detection signal (output
14
) is input to an unillustrated control circuit. The control circuit performs various controls in accordance with the detection signal from the sensor
11
.
It is essential that the fixed resistor R
11
and the variable resistor R
12
in the conventional sensor sensitivity adjusting apparatus have approximately the same resistance ratio and approximately the same temperature characteristic. If the temperature characteristics of the two resistors R
11
and R
12
differ from each other, the reference voltage V
1
shifts from the desired value when the temperature changes. This changes the value of the current I
1
, causing the sensitivity of the sensor
11
to deviate from the desired sensitivity. It is therefore troublesome to select a usable fixed resistor R
11
and variable resistor R
12
.
Many components (five in FIG.
1
), such as the fixed resistor R
11
, the variable resistor R
12
, the fixed resistor R
13
, the operational amplifier
12
and the amplifier circuit
13
, are provided on a printed circuit board. The printed circuit board is relatively large and the attachment of these components is tiresome, thus leading to a relatively high manufacturing cost.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a compact sensor sensitivity adjusting apparatus having fewer components.
To achieve the above object, the present invention provides an apparatus for adjusting a sensitivity of a sensor. The apparatus includes a sensor, a current supplying circuit, a voltage applying element, and a current defining element. The sensor is activated when supplied with a predetermined drive current. The sensitivity of the sensor is changed in accordance with a value of the drive current. The current supplying circuit is connected to the sensor and supplies the drive current to the sensor based on a reference voltage. The voltage applying element has a plurality of fixed resistors, which are connected to the current supplying circuit. The voltage applying element generates the reference voltage applied to the current supplying circuit. The current defining element has a variable resistor, which is connected to the current supplying circuit and the sensor. The current defining element defines a value of a current flowing in the sensor. A sensor voltage approximately equal in a value to the reference voltage is applied to the current defining element.
REFERENCES:
patent: 4379406 (1983-04-01), Bennewitz et al.
patent: 5818225 (1998-10-01), Mickley et al.
Kogiso Katsuya
Matsui Kazuhito
Nishibe Yasushi
Buyan Robert D.
Kabushiki Kaisha Tokai Rika Denki Seisakusho
Nguyen Vincent Q.
Oda Christine
Stout, Uxa Buyan & Mullins, LLP
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