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A new design for an accurate high-voltage d-c standard resistor has been dc \·ised. It is made up of a large number of individua ll y s hielded, one-megohm wire-wound resisto rs connected in series a nd arran ged to form a vertical helix between a ground plate a nd a highvoltage electrode. The indi vidual shields co mplete ly enclose each one-megohm resistor and prevent formation of corona at t he surface of t he resistance co il no matter how high the potential of t he hield is above g round . The vert ical helical configu ration with a large " hat," or high-voltage electrode, on top serves to prevent conce nt rat ion of electri c field a nd corona formation at t he high-potentia l end of t he resistor. A 200-megohm uni t, constructed during 1955 a nd t ried out up to 100 kv in 1956, indicated t he des ign to be free of corona errors but, for t he part icular one-megohm resistors used, the variation with temperat ure \Va qui te la rge (0.01 percent per 0G). A 100 mego hm unit usin g lowtemperature coefficient res istors has been recently constru cted a nd tested up to 100 k v. An experimenta l method of checking for corona or leakage errors at high values of voltage was developed. It consisted of accurately comparing the current "in" at t he high voltage end of the resistor with t he cLllTent "out" at t he ground end for se veral different values of app lied voltage. These measurements together with others performed to check temperature a nd lea kage errors indicated t hat the valu e of res istance for t he 100-megohm unit rema ins co nstant to within abo ut 10 ppm for voltagcs up to 50 kv under ordinary laboratory conditions. At 100 kv t he maximum error (caused by heating) was estimated to be a bout 40 ppm.

Special shielded resistor for high-voltage d-c measurements