Oil level control system

An oil level control device for each compressor of a multiple compressor refrigeration system, said system including an oil supply, each control device being adapted to be attached between an associated compressor sump and the oil supply, each control device comprising:

• a) a housing, including an inlet communicating with the oil supply and an outlet communicating with an associated compressor sump;
• b) flow control means controlling flow from the oil supply into said compressor sump;
• c) a proximity detection system including a sensing chamber and a fixed, insulated metallic probe for detecting the presence of oil in the chamber and generating a signal that controls the supply of oil to said compressor sump to maintain the correct oil level in the sump;
• and
• d) control circuit means connected to the probe, said control circuit means having an output operating the flow control means.
• (e) the proximity detection system comprising oscillator means for producing an output signal, the oscillator means comprising a transistor having a base, an emitter and a collector, the transistor having an open and a closed loop gain and a base-emitter junction that rectifies resonant signals at the collector to produce the output signal, the oscillator means further comprising negative feedback means for reducing the sensitivity of the closed loop gain to variations in the transistor's open loop gain and for stabilizing the frequency of the oscillator means;
• (f) the probe being operatively coupled to the oscillator means for varying the level of the oscillator output signal in response to electrical properties of the oil;
• and
• (g) the control circuit means being operatively coupled to the oscillator means to receive the oscillator output signal and being responsive to variations of predetermined magnitudes of the amplitudes of the oscillator output signal for detecting the presence or level of the oil.