Apparatus and method for automatic digitizer fault detection

A method for detecting a change in resistance across one conductive layer of a digitizer having two normally-separated conductive layers comprising the steps of:

• measuring a first resistance value between first and second end electrodes of the one conductive layer while the one conductive layer is separated from the other conductive layer:
• storing the first resistance value;
• measuring a second resistance value between the first and second end electrodes of the one conductive layer while the one conductive layer is separated from the other conductive layer;
• comparing the second resistance value with the previously stored first resistance value;
• indicating a pass indication if the difference between the second resistance value and the previously stored first resistance value is less than a predetermined number;
• and
• indicating a fail indication if the difference between the second resistance value and the previously stored first resistance value is greater than the predetermined number.

A method for detecting a change in uniformity of resistance across one conductive layer of a digitizer having two normally-separated conductive layers comprising the steps of:

• measuring a first voltage value at a test electrode on the one conductive layer between first and second end electrodes of the one conductive layer while the one conductive layer is separated from the other conductive layer;
• storing the first voltage value;
• measuring a second voltage value at the test electrode on the one conductive layer while the one conductive layer is separated from the other conductive layer;
• comparing the second voltage value with the previously stored first voltage value;
• indicating a pass indication if the difference between the second voltage value and the previously stored first voltage value is less than a predetermined number;
• and
• indicating a fail indication if the difference between the second voltage value and the previously stored first voltage value is greater than the predetermined number.

A method for detecting a change in separation resistance between first and second conductive layers within a digitizer comprising the steps of:

• measuring a first resistance value between an end electrode on the first conductive layer and an end electrode on the second conductive layer of the digitizer while the first conductive layer is separated from the second conductive layer;
• storing the first resistance value;
• measuring a second resistance value between the end electrode of the first conductive layer and the end electrode of the second conductive layer of the digitizer;
• comparing the second resistance value with the previously stored first resistance value;
• and
• indicating a pass indication if the second resistance value is less than the previously stored first resistance value.

A method for detecting faults within a digitizer comprising the steps of:

• measuring a voltage value between first and second conductive layers;
• measuring a predetermined number of additional voltage values between the first and second conductive layers;
• summing the deviations of the additional voltage values from the one voltage value;
• comparing the sum of the deviations with a predetermined threshold deviation;
• indicating a pass indication if the sum of the deviations is less than the predetermined threshold;
• and
• indicating a fail indication if the sum of the deviations is greater than the predetermined threshold.

An apparatus for detecting faults in a digitizer having an operative electrode comprising:

• source means for energizing the digitizer;
• an analog-to-digital converter coupled to the digitizer and to the source means;
• a controller coupled to the output of the analog-to-digital converter for performing fault detection routines;
• switch means for selectively connecting the source means and the analog-to-digital converter to the digitizer;
• and
• a test electrode within the digitizer coupled to the analog-to-digital converter.

A method for detecting faults within a digitizer comprising the steps of:

• measuring a resistance value between a first conductive layer and a second conductive layer of the digitizer;
• comparing the resistance value with a previously stored threshold resistance value;
• indicating a pass indication if the resistance value is less than the previously stored resistance value;
• measuring a predetermined number of additional resistance values between the first and second conductive layers;
• summing the deviations of the additional resistance values from the one resistance value;
• comparing the sum of the deviations to a predetermined threshold deviation;
• indicating a fail indication if the sum of the deviations is less than the predetermined threshold deviation;
• and
• repeating the method if the sum of the deviations is greater than the predetermined threshold deviation.