Proximity sensor combining impedance, frequency and decay constant information
AssigneeRockwell Automation Technologies, Inc.
InventorRobert J Pond
Life of this patent
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Abstract
Systems and methods are disclosed that compensate for temperature drift in a proximity sensor, such as an extended range inductive proximity sensor. Voltage measurement can be taken before, and during damped oscillatory decay of a voltage in a resonant circuit in the proximity sensor to determine a value, γ, associated with an inductive time constant for the resonant circuit. A target-induced inductance value can be isolated, via manipulation of the gamma value, and compared to a predetermined threshold value to determine whether the target has been sensed by the proximity sensor.
Claims22
A system that compensates for temperature drift in a sensing coil in an extended range inductive proximity sensor, comprising:
- a measuring component that measures voltages in a resonant damping circuit in the proximity sensor before and during a damped oscillatory voltage phase;
- and
- a control component that analyzes information associated with the measured voltages to derive a gamma value related to a time constant of the resonant damping circuit and isolates a portion of inductance caused by a target to determine whether the target has been sensed.
A method for compensating for temperature drift in a proximity sensor, comprising:
- determining an RC time constant for a resonant circuit in the proximity sensor;
- pulsing a current for a period of approximately one RC time constant through the resonant circuit to charge a capacitor therein and to mitigate current consumption by the proximity sensor;
- determining a first voltage across the resonant circuit;
- causing the voltage across the resonant circuit to decay for a predetermined time period;
- and
- determining a second voltage across the resonant circuit after the predetermined time period.
A system that compensates for temperature drift effects on a sensing coil in an extended range proximity sensor, comprising:
- means for determining a time constant value for a resonant damping circuit in the proximity sensor;
- means for determining a portion of total circuit inductance due to a target;
- and
- means for comparing the value of the target-induced inductance value to a predetermined threshold value.
Dependencies are inferred from the claim text.