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Software Adjustment of Gain and Offset Analog Errors

IP.com Disclosure Number: IPCOM000102037D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 67K

Publishing Venue

IBM

Related People

Kist, TA: AUTHOR [+2]

Abstract

The proposed software will eliminate many linear errors in Data Acquisision Systems (systems that convert analog signals into digital values). In previous systems, the accuracy of the conversion process relied on the precision of the analog devices (Operational Amplifiers, Sample and Hold Amplifiers, Analog-to-Digital Converters, etc.). These devices initially have gain and offset errors which drift over the life of the system. Precision systems are often adjusted to eliminate these errors. Potentiometers are generally used at beginning of life to calibrate for these errors; however, the system is still subject to drift. The following software routine will continually calibrate the system over its life, thus eliminating the need for manual calibration and increased end of life accuracy.

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Software Adjustment of Gain and Offset Analog Errors

       The proposed software will eliminate many linear errors
in Data Acquisision Systems (systems that convert analog signals into
digital values).  In previous systems, the accuracy of the conversion
process relied on the precision of the analog devices (Operational
Amplifiers, Sample and Hold Amplifiers, Analog-to-Digital Converters,
etc.).  These devices initially have gain and offset errors which
drift over the life of the system.  Precision systems are often
adjusted to eliminate these errors.  Potentiometers are generally
used at beginning of life to calibrate for these errors; however, the
system is still subject to drift.  The following software routine
will continually calibrate the system over its life, thus eliminating
the need for manual calibration and increased end of life accuracy.

      The specific Data Acquisition System discussed measures
resistance, but the methodology used is applicable to other systems.
The software requires two test voltages to be available in hardware.
These test points are used to calibrate out the linear errors in the
system.  The system takes the analog signal as input and converts it
to a digital output (see Fig. 1).  Ideally, the function would be a
line starting at the origin and having a gain of one.  In practice,
the function has a slight offset and a gain other than one.  The
proposed method takes the two test points and cancels these errors.
The two p...