Oscillator with a temperature compensated oscillating coil

A temperature compensated oscillator comprising:

• an oscillating circuit including an oscillating coil having a temperature dependent copper resistance, said oscillating circuit having a resonant frequency;
• a negative resistance connected across said oscillating circuit;
• a constant alternating current source for supplying current at said resonant frequency to said oscillating circuit, said constant alternating current producing across the copper resistance a temperature dependent voltage drop proportional to said temperature dependent resistance wherein said voltage drop compensates for any temperature induced variation in amplitude of a voltage across said oscillating circuit.

A proximity switch comprising:

• an oscillator including an oscillating circuit having an oscillating coil with a temperature dependent resistance, said oscillating circuit having a resonant frequency and a negative resistance connected across said oscillating circuit;
• a constant alternating current source for supplying said oscillating circuit with current at said resonant frequency, said constant alternating current producing in the temperature dependent resistance of said oscillating coil a temperature dependent voltage drop effective to compensate for any temperature variation in the amplitude of a voltage across said oscillating circuit;
• said proximity switch being responsive to a driving blade for driving said proximity switch according to a switching distance between said driving blade and said oscillating coil, said switching distance determining a switching on and off of said oscillator, and said temperature variation compensation of the voltage across the oscillating circuit providing an increased effective switching distance.