100b 102b and 104b and gain control variable resistors 100c 102c and 104c complete the respective comparator amplifier circuits the output signal of the amplifiers respectively then is the logic circuit 82 is comprised of four and gates 106 108 110 and 112 and one or gate 114 and two amplifiers 116 and 118 to drive the gates the operation of the logic circuit may be most readily understood by considering the table ii below table ii______________________________________condition indication circuit logic output gate logic input signals______________________________________hi oil 106 d sub 32 u00b7 d sub 31 u00b7 d sub 21 ok oil 108 d sub 32 u00b7 d sub 31 u00b7 d sub 21lo oil 110 d sub 32 u00b7 d sub 31 u00b7 d sub 21 inversion 114 d sub 32 u00b7 d sub 31 d sub 21 ______________________________________the bar notation indicates the reverse sign of the signalvoltage thus d sub 32 minus d sub 32 the output of the gates 106 108 110 and 112 are used to actuate the system status visual display the memory the memory display and the main switch cut off a second preferred embodiment of my invention is shown in fig3 a refrigeration system compressor 130 is shown in partly cutaway perspective view the compressor 130 is similar in all respects to the compressor illustrated in fig1 at reference numeral 10 the compressor 130 is comprised of a crankcase 132 within which a crankshaft 134 and connecting rod 136 mounted to the crankshaft lubricating oil 140 is retained within the interior of the crankcase in normal operation some.