require an operator to manually balance the bridge the sensor circuit used in this invention involves only a simple rc voltage divider wherein the current is driven to the grounded 25 mold 18 the opposing capacitor plate through the curing rubber a load resistor 19 typically 200 k ohm is placed in line with the flow of current and the resultant voltage 20 v2 across the resistor 19 is measured with a high precision amplifier by simultaneously measuring the applied voltage also known as the excitation voltage it is then possible to readily determine the amount of attenuation and phase shift resultant from the flow of complex current fig3 illustrates the sensor electrical circuit where the applied excitation voltage 21 v0 sin u03c9t is placed at one terminal of the amplifier and this potential drives a complex current i through the load resistor 19 r and then finally through the capacitor formed by the sensor 24 rubber compound 23 and the electrically grounded 25 mold 18 the following description assumes a voltage amplitude of 1 volt for the excitation v0 however all the subsequent analysis remains the same if the voltage is not unity in the non unity cases k becomes the ratio of.