Remote sensor with compensation for lead resistance
AssigneeCaterpillar Inc.
InventorMaurice E. Schaefer
Life of this patent
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Abstract
An apparatus increases the accuracy of a signal delivered from a remote analog sensor to an analog to digital converter. The output of the sensor is derived from a ratio between the power applied and the sensed parameter; thus, any changes to the power applied affects the accuracy of the sensor output. It is, therefore, advantageous to closely control the voltage applied to the sensor. The apparatus monitors the voltage drop across the lead lines which extend between the sensor and a power supply and increases the voltage applied to the sensor by a magnitude corresponding to the lead line voltage drop. The accuracy of the sensor is preserved independent of the lead line length and resistance.
Claims12
An apparatus for compensating for a resistance induced voltage drop across a first and a second lead line, each of said first and second lead lines having first and second ends respectively connected to opposite terminals of a resistive type sensing element and said apparatus, said apparatus comprising:
- first means for sensing the magnitude of the resistance of said first lead line and delivering a first voltage signal to said second end of said first lead line, said first voltage signal having a magnitude responsive to the magnitude of said first lead line resistance;
- and
- second means for sensing the magnitude of the resistance of said second lead line and delivering a second voltage signal to the second end of said second lead line, said second voltage signal having a magnitude responsive to the magnitude of said second lead line resistance.
An analog to digital conversion circuit having an interface circuit for automatically compensating for a voltage drop across a resistance associated with a lead line between a remotely located sensor having an input, an output, and a tap, and an analog to digital converter, comprising:
- said sensor having an input, an output, and a tap;
- a precision voltage source;
- a buffer having an output and a high impedence input connected to said sensor input;
- a first comparator having a noninverting input connected to said precision voltage source, an inverting input connected to the output of said buffer, and an output connected through said lead line to said sensor input;
- a second comparator having an inverting input connected to said output of said sensor, a noninverting input connected to system ground, and an output connected to said output of said sensor;
- an analog to digital converter having an input connected to the tap of said sensor and a reference voltage input connected to the output of said buffer;
- a current sensing resistor connected between the output of said second comparator and the output of said sensor;
- a differential amplifier having first and second inputs and an output, said first and second inputs being connected to alternate ends of said current sensing resistor;
- a plurality of comparators, each having a noninverting input connected to the output of said differential amplifier, an inverting input connected to a respective one of a plurality of reference voltages, and an output;
- and
- a processing means for receiving signals from the outputs of said analog to digital converter and said plurality of comparators and converting said signals to a control signal responsive to the magnitudes of said converter and comparator output signals.
Dependencies are inferred from the claim text.