Sensing the temperature of a printhead in an ink jet printer
First Claim
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1. A method for improving the accuracy of a temperature sensing thermistor integrated into a substrate comprising the steps of:
- forming a temperature sensing thermistor on the substrate;
the thermistor forming one leg of a bridge circuit and having a resistance R1 =Rt =ro (1+aΔ
T) where a is the temperature coefficient of resistance (TCR);
ro is the resistance at a set point temperature To and Δ
T is the difference in temperature between the temperature T to be measured and the set point temperature To,forming a plurality of fractional thermistors adjacent the temperature sensing thermistor such that their TCR values are substantially identical to that of the temperature sensing thermistor, and having a combined resistance of fR1 where f=1-B/a, where B is a preselected minimum TCR value, andincluding the fractional thermistors and an external resistance Rx =ro (1-f) in a leg of the bridge circuit which is adjacent to the R1 leg which contains the temperature sensing thermistor.
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Abstract
An improved temperature compensation method is disclosed in which a temperature sensing thermistor is formed on a substrate whose temperature is to be series of fractional thermistors which are selectively shorted out during a manufacturing process to provide a compensation for manufacturing variabilities of the temperature coefficient of resistance of the thermistor.
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4 Claims
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1. A method for improving the accuracy of a temperature sensing thermistor integrated into a substrate comprising the steps of:
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forming a temperature sensing thermistor on the substrate;
the thermistor forming one leg of a bridge circuit and having a resistance R1 =Rt =ro (1+aΔ
T) where a is the temperature coefficient of resistance (TCR);
ro is the resistance at a set point temperature To and Δ
T is the difference in temperature between the temperature T to be measured and the set point temperature To,forming a plurality of fractional thermistors adjacent the temperature sensing thermistor such that their TCR values are substantially identical to that of the temperature sensing thermistor, and having a combined resistance of fR1 where f=1-B/a, where B is a preselected minimum TCR value, and including the fractional thermistors and an external resistance Rx =ro (1-f) in a leg of the bridge circuit which is adjacent to the R1 leg which contains the temperature sensing thermistor. - View Dependent Claims (2, 3, 4)
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Specification