Sensor calibration

Details Sensor calibration Sensor calibration

1999-09-16

2001-10-16

Gutierrez, Diego (Department: 2859)

Data processing: measuring, calibrating, or testing

Calibration or correction system

Sensor or transducer

C702S099000, C073S001880, C073S001610, C033S702000

Reexamination Certificate

active

06304827

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to the calibration of electronic sensors.
Electronic sensors are employed in a number of different fields of technology. Such sensors may be employed to detect changes in environmental parameters, such as atmospheric pressure, or may be employed to detect changes in forces applied to the object to which they are attached, for example.
Whilst there are very many different types of sensor, one problem common to most is that of temperature sensitivity. Variation of the sensor output with temperature can cause considerable difficulty both in terms of provision of sufficient accuracy and also in relation to the generation of erroneous warning signals.
One approach to compensate for temperature variations is to calibrate each sensor individually during manufacture. This means, however, a considerable increase in production costs.
In recent times an alternative approach to temperature compensation has been proposed. In this alternative approach the sensor itself or its associated circuitry is provided with means for calculating and providing an offset to the output of the sensor dependent upon the temperature. Such an approach requires mathematical modelling of the sensor output with respect to temperature. Such an approach has problems, however, in that the algorithm employed to model the sensor output requires complex division of high order functions in order to be able to provide accurate modelling. It will be appreciated that the requirement for division increases the compensation circuit complexity and increases processing time.
SUMMARY OF THE INVENTION
The present invention seeks to overcome the above problems.
According to the present invention there is provided a device for compensating for temperature dependent effects on an electronic sensor output signal, the device comprising:
means for receiving a digital output signal from an electronic sensor;
means for receiving a digital signal indicative of the temperature of the sensor; and
means for producing an output signal dependent upon the received sensor and temperature signal and based upon the compensation polynomial H(V,T), where:
H
⁡
(
V
,
T
)
=
1
G
·
S
0
⁡
[
V
·
(
1
+
∑
i
=
1
m
⁢
 
⁢
S
i
⁢
T
i
)
-
Z
0
-
∑
j
=
1
n
⁢
 
⁢
Z
j
⁢
T
j
]
where T is temperature, V is the output of the sensor, G is a gain value, S
0
is the sensitivity at a fixed value of T=0, Z
0
is the sensor offset voltage at a value of T=0, S
i
is the i
th
order coefficient of sensitivity temperature drift, Z
j
is the j
th
order coefficient of offset temperature drift and m and n are integers, S
m
and Z
n
being the highest order coefficients.
With the device of the present invention an output signal can be generated by employing simple digital signal processing circuitry without the need for division. Not only does this reduce the complexity required but it also improves the accuracy of the compensation.
The real temperature at which T=0 can be set at any real value, but is preferably a median value (for example 25° C.) for the operating environment of the sensor.
Ideally highest order coefficients, S
m
and Z
n
, are second order, ie. S
2
and Z
2
, however it will be appreciated that higher order coefficients such as S
3
and Z
3
may be employed in order to further increase accuracy, although these will, of course, increase circuit complexity. Highest order coefficients of lower order may also be used for simplicity, although this will, of course, decrease accuracy.
The device may be formed as an integral part of the sensor, or may be formed separately.
A corresponding method of generating a temperature compensated signal is also provided.


REFERENCES:
patent: 4072051 (1978-02-01), Peterson
patent: 4949469 (1990-08-01), Wachtler
patent: 5247467 (1993-09-01), Nguyen et al.
patent: 5559431 (1996-09-01), Sellen
patent: 5848383 (1998-12-01), Yunus
patent: 6055489 (2000-04-01), Beatty et al.

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