Self contained test probe employing high input impedance

Claim 1

A self contained, portable hand holdable apparatus for testing the conducting state of a conductor without requirement of direct contact, comprising 1. fountain pen sized container means of a hollow elongated tube like means having two ends and wherein are hermetically sealed the following components: 2. probe means located towards one end of said two ends of said container and having an electrode portion and an insulator portion covering said electrode portion; 3. indicator means located toward said one end in close physical proximity to said electrode of said probe means and insulated therefrom; 4. circuit means containable in said container means and comprising a field effect transistor having a gate input electrode, a drain electrode and a source output electrode, said field effect transistor being connected in source follower circuit configuration and having an input impedance of 20,000 to 30,000 megohms, provided by the space charge of said field effect transistor without any added biasing means, said gate input electrode being directly connected to said electrode of said probe means and having no other circuit connections thereto, at least one amplifier transistor means having an input electrode connected to the source output electrode of said field effect transistor and an output electrode connected to said indicator means, and means for biasing said field effect transistor and said amplifier transistor means, whereby said apparatus can be readily picked up and moved by the fingers of a hand with said probe means placed in the vicinity of an electrostatic field emanating from a low voltage energized conductor to cause said field effect transistor to cutoff and in turn cause said amplifier transistor means to conduct and hence cause flow of current to said indicator means whereby high sensitivity is attained.