corresponds to the electric field received at each sensor plate 28 human tissue is conductive due to the large percentage of water that makes up the human body therefore when human or other animal tissue such as a hand or other body part enters the electric field some of the field is shunted to the body 39 s stray capacitance this results in a significant reduction i e lowering of the displacement current of the electrical signal generated by the sensor plate s 28 near the human tissue however rubber is an insulator i e non conductive therefore when rubber or another insulator enters the electric field no significant reduction of the displacement current occurs said another way the change in displacement current is different in sign for human tissue than for rubber therefore the sensor assembly 20 is operative to discriminate between human tissue and the insulating material being processed in the machine such as rubber sensor assembly 20 also may include an amplifier 42 for amplifying the electric signal produced by sensor plates 28 amplifier 42 may be electrically connected to each sensor plate 28 for amplifying the electrical signal each amplifier 42 is preferably physically as close as possible to the sensor plate 28 to avoid contamination of the electrical signal from sources of electrical interference in the preferred embodiment the amplifiers 42 are disposed in channel 36 of the support member 34 as best seen in fig3 a sensor bridge piece 44 electrically connects the sensor plate 28 and the amplifier 42 through a hole.