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Abstract

A passive voltmeter for high voltage transmission lines that accurately measures and displays a wide range of voltages. A d'Arsonval type meter movement is preferably used in conjunction with the voltmeter wherein the scale contains a linear range and a compressed, nearly-logarithmic range. A circuit controls the pointer so that the deflection is linear for a low range of voltages while a high range of voltages is deflected in a compressed manner. The term 'compressed' means that the display is scaled in a logarithmic manner although not a true logarithmic function. The circuit comprises one or more parallel branches with a meter movement and a resistor in the first branch; each additional branch, if more than one, contains a resistor and at least one diode connected in series. The additional branches have an increasing number of serially connected diodes so that the turn-on voltage for each branch increases with additional branches, while the resistors contain a decreasing values of resistance for each additional branch. The passive voltmeter comprises a housing internally coated with a conductive material, a high resistance prong extending from the housing, and a meter movement connected to the housing. As the prong touches the line, a capacitive charge is formed with the housing as the first plate and the physical surroundings as the second plate. The meter movement is deflected by the charging current since the current will be proportional to the voltage in the transmission line.

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