Load current monitoring device for detecting predetermined degree of change in load impedance

A device for detecting changes in load impedance by detecting changes in load current that are not induced by fluctuations in the applied load voltage comprising:

• means for monitoring the current provided to the load, said current monitoring means providing a dc voltage signal having an amplitude proportional to the amount of load current;
• means for monitoring the voltage applied to the load, said voltage monitoring means providing another dc voltage signal having an amplitude porportional to the amount of load voltage;
• means for defining at a selected desired value of load impedance a reference function of monitored load current against monitored load voltage throughout a range of load voltages to thereby establish a reference value of current for each value of load voltage throughout said range;
• and
• means for comparing at any value of monitored load voltage within said range the present value of the load current then monitored with the reference value called for by said defined function, whereby any difference indicated by said comparison signifies a change in load current independent of load voltage fluctuations, and therefore signifies a change in load impedance.

A device for detecting changes in a generally constant load impedance by detecting changes in load current that are not induced by fluctuations in the applied load voltage, comprising:

• means for generating a first dc voltage signal whose value is indicative of the amount of current provided to the load;
• means for generating a second dc voltage signal whose value is indicative of the amount of voltage applied to the load, one of said signals increasing at a rate generally equal to the rate of decrease in the other of said signals when said impedance is generally constant and said load voltage fluctuates;
• means for algebraically summing the first and second signals, the summing means providing a generally constant value third dc voltage signal proportional to the generally constant load impedance;
• and
• means responsive to the third signal for indicating that the third signal value has deviated to a predetermined degree from its normally constant value, thus indicating an abnormal fluctuation in the generally constant load impedance.