Measuring device using impedance variation of r. f. bridge coils with temperature compensation by flowing d.c. current through the coils

Claim 1

MEASURING APPARATUS COMPRISING AN R.F. BRIDGE ENERGIZED BY A SOURCE OF RADIO FREQUENCY ENERGY, TWO COIL CIRCUITS FORMING TWO LEGS OF THE BRIDGE, MEANS CONNECTED TO THE BRIDGE TO PROVIDE OUTPUT SIGNALS IN ACCORDANCE WITH VARIATIONS IN THE ELECTRICAL IMPEDANCE OF THE COIL CIRCUITS, A TEMPERATURE COMPENSATING NETWORK INCLUDING THE TWO COIL CIRCUITS TO GENERATE COMPENSATING SIGNALS REPRESENTATIVE OF VARIATIONS IN THE RESISTANCE OF THE COIL CIRCUITS RESULTING FROM THEIR TEMPERATURE CHANGES, SAID TEMPERATURE COMPENSATING NETWORK INCLUDING MEANS TO FLOW D.C. CURRENT THROUGH THE COIL CIRCUITS, MEANS TO ISOLATE PORTIONS OF THE TEMPERATURE COMPENSATING NETWORK FROM THE R.F. SIGNALS, AND DETECTOR MEANS RESPONSIVE TO THE OUTPUT SIGNALS OF THE R.F. BRIDGE AND TO THE COMPENSATING SIGNALS TO GENERATE SIGNALS REPRESENTIVE OF THE ELECTRICAL IMPEDANCE OF THE COIL CIRCUITS.