resistance standard (1.0 Ohm)
Date: 1880-1910
Inventory Number: 0302e
Classification: Resistance Standard
Subject:
Maker: Otto Wolff (fl. 1870 - 1920)
Owner: Harvard Engineering School (1918 - 1951)
Cultural Region:
Place of Origin:
City of Use:
Dimensions:
15.2 cm (6 in.)
Material:
Description:
Coil of manganin wound on a tube supported in a perforated nickel-plated case. Two heavy terminals and one center knob protrude from the hard rubber top for suspension in mercury to a standard bridge set in an oil bath. There is a thermometer inside the container as well.
The resistance is 0.1 Ohms and is calibrated for 20°C.
The resistance is 0.1 Ohms and is calibrated for 20°C.
Signedinscribed on top: O. Wolff
Inscribedtop of the cylinder inscribed: 1.0 Ohms / bei 20°C / Manganin / O. Wolff Berlin / Germany / 4474;
side of cylinder inscribed: H.U. 121-A
side of cylinder inscribed: H.U. 121-A
FunctionA resistance standard is not to measure the resistance of an electric conductor but rather to compare such a conductor to a temperature-fixed resistance. In other words, such a device is used to determine the value of an unknown current. To do so, a current in the conductor would pass through mercury (for the older type of standard resistance), into which the two leads from the resistor dip. The manganin wire in this instrument was baked before being dipped into paraffin so that all moisture is removed and to improve the insulation over the wire.
This one was used with other similar resistances of different values and a bridge to connect several of them together.
From Card:
"Ref. An adaptation of the standard use in 1865 (See report Standards Committee - british 1873, p136.pl.4). At the time wire of 2/3 silver and 1/3 platinum were used. Coil surrounded by wire and suspended in water bath. (See also J.E.H. Gordon. Elec & Mag [London 1883] p.267. p321, pl.24). This variety has replaced the earlier form."
This one was used with other similar resistances of different values and a bridge to connect several of them together.
From Card:
"Ref. An adaptation of the standard use in 1865 (See report Standards Committee - british 1873, p136.pl.4). At the time wire of 2/3 silver and 1/3 platinum were used. Coil surrounded by wire and suspended in water bath. (See also J.E.H. Gordon. Elec & Mag [London 1883] p.267. p321, pl.24). This variety has replaced the earlier form."
Curatorial RemarksThis Resistance Standard was not found during 1997 inventory project nor during 2007-2008 shelf reading project. See CHSI 8" x 10" inventory card for 0302 for information about this object.
ProvenanceFrom the Harvard Engineering School. Brought to the Collection 11/56.
