Calibration method and apparatus for an electronic weight indicator

A method calibrating and correcting for changes after calibration in an electronic weight indicator adapted to convert an analog output of a load cell into a display with the aid of a digital computer comprising the steps:

• a. initially calibrating the weight indicator to display, in digital form, a range of weights the analog signal of which is produced by the load cell including inputting the computer with a data base including at least:
• 1. a zero reference measurement;
• 2. a deadlock correction offset measurement;
• 3. a span measurement of the analog and A/D circuitry;
• b. applying the output of the load cell to an instrumentation amplifier;
• c. applying a programmable offset to the instrumentation amplifier to provide automatic deadload compensation said programmable offset is determined by a count contained in a counter;
• d. correcting for drift in accordance with the algorithm:
• ##EQU8## if the deadload correction is positive or:
• ##EQU9## if the deadload correction is negative.

A method calibrating and correcting for changes after calibration in an electronic weight indicator adapted to convert an analog output of a load cell into a display with the aid of a digital computer comprising the steps:

• a. initially calibrating the weight indicator to display, in digital form, a range of weights the analog signal of which is produced by the load cell including inputting the computer with a data base including at least:
• 1. a zero reference measurement;
• 2. a deadload correction offset measurement;
• 3. a span measurement of the analog and A/D circuitry;
• b. applying the output of the load cell to an instrumentation amplifier;
• c. applying a programmable offset to the instrumentation amplifier to provide automatic deadload compensation;
• d. correcting for drift in accordance with the algorithm:
• ##EQU10## if the deadload correction is positive or:
• ##EQU11## if the deadload correction is negative in which algorithm is contained in a read-only-memory (ROM) of a microprocessor;
• and in which the microprocessor controls a counter containing a count for controlling the programmable offset applied to the instrumentation amplifier.

A method calibrating and correcting for changes after calibration in an electronic weight indicator adapted to convert an analog output of a load cell into a display with the aid of a digital computer comprising the steps:

• a. initially calibrating the weight indicator to display, in digital form, a range of weights the analog signal of which is produced by the load cell including inputting the computer with a data base including at least:
• 1. a zero reference measurement;
• 2. a deadload correction offset measurement;
• 3. a span measurement of the analog and A/D circuitry;
• b. applying the output of the load cell to an instrumentation amplifier;
• c. applying a programmable offset to the instrumentation amplifier to provide automatic deadload compensation;
• d. correcting for drift in accordance with the algorithm:
• ##EQU12## if the deadload correction is positive or:
• ##EQU13## if the deadload correction is negative in which the zero reference measurement is obtained from a load cell ground.

A method calibrating and correcting for changes after calibration in an electronic weight indicator adapted to convert an analog output of a load cell into a display with the aid of a digital computer comprising the steps:

• a. initially calibrating the weight indicator to display, in digital form, a range of weights the analog signal of which is produced by the load cell including inputting the computer with a data base including at least:
• 1. a zero reference measurement;
• 2. a deadload correction offset measurement;
• 3. a span measurement of the analog and A/D circuitry;
• b. applying the output of the load cell to an instrumentation amplifier;
• c. appying a programmable offset to the instrumentation amplifier to provide automatic deadload compensation;
• d. correcting for drift in accordance with the algorithm:
• ##EQU14## if the deadload correction is positive or:
• ##EQU15## if the deadload correction is negative in which the span reference (M Gref) is obtained from a resistor network.

An electronic weight indicator adapted to convert an analog output of a load cell into a digital display comprising:

• a. means converting the analog output of the load cell to a digital display including an analog-to-digital converter;
• b. means to correct for changes after calibration in the analog and digital circuitry including temperature induced drift and drift produced by component changes, said means including:
• 1.
• (a) A microprocessor having a read-only memory containing an algorithm for obtaining a deadload correction offset measurement,
• (b) said microprocessor controls a counter containing a count for providing the deadload correction offset measurement.
• 2. means for obtaining a zero reference measurement,
• 3. means for obtaining a span measurement of the analog and digital circuitry,
• 4. means to multiplex the zero reference measurement, the deadload offset correction measurement and span measurement with the load cell output, and
• 5. means to correct the drift in accordance with:
• ##EQU16## if the deadload correction is positive, or ##EQU17## if the deadload correction is negative, where M=corrected measurement of load cell output,
• M Sig=uncorrected measurement of load cell output,
• M Zero=zero reference measurement,
• M Gref=2 ppm/.degree.C. reference measurement,
• M Bias=measurement of deadload correction.