thermo-voltmeter
Datecirca 1930
Inventory Number0318
ClassificationVoltmeter
Subject
Maker
Weston Electrical Instrument Corporation
founded 1888
Cultural Region
Place of Origin
Dimensions11.5 × 23.6 × 23.5 cm (4 1/2 × 9 5/16 × 9 1/4 in.)
Material
Accessoriesstandardization certificate of 1930 on inside of lid
DescriptionA voltmeter for radiofrequency uses consisting of a hinged wooden box that closes with leather straps, which contains an indicator covered by a bakelite panel with an arc-shaped window. The indicator consists of a scale with two different sets of numbers: one set is black going from 0 to 20 and the other is red going from 0 to 5. Both are nonlinear, increasing more slowly as the numbers get larger. There is an arc-shaped mirror that spans the length of the scale.
Above the scale moves a needle which is held by a moving vane that is connected to an item labeled "HEATER (+) and HEATER (-)" by two electric cables. All these are hidden from view by the bakelite panel, and are connected to it by several cables that correspond to buttons on the panel. The four buttons are labeled 5v (red), 20v (black), 20v (black) and 5v (red). A screw labeled "CORRECTION" stands on the panel right above the vane that holds the needle.
Above the scale moves a needle which is held by a moving vane that is connected to an item labeled "HEATER (+) and HEATER (-)" by two electric cables. All these are hidden from view by the bakelite panel, and are connected to it by several cables that correspond to buttons on the panel. The four buttons are labeled 5v (red), 20v (black), 20v (black) and 5v (red). A screw labeled "CORRECTION" stands on the panel right above the vane that holds the needle.
Signedon scale: WESTON THERMO-VOLTMETER / RADIO FREQUENCY / THERMO-COUPLE TYPE MODEL 492 NO. 268.
on plaque: WESTON / MODEL [illegible] No. 268 / WESTON ELECTRICAL INSTRUMENT CORP. / NEWARK, N.J., U.S.A.
Inscribed
along inner rim of scale: "PATENTED NOV.6, 1921."
FunctionThis is a voltmeter for very high AC voltages for radiofrequency uses. It measures the voltage indirectly (AC voltage cannot be measured directly by a galvanometer as it changes polarization rapidly) by heating up a filament and then using a thermocouple to find out its temperature, which is proportional to the voltage going through it. The standardization certificate works as a correction chart when the instrument is used at ambient temperatures other than 23°C.
The voltmeter has several buttons to change its range between 5 and 20 volts.
The voltmeter has several buttons to change its range between 5 and 20 volts.
ProvenanceFrom the School of Engineering, Harvard University.
Harvard Cyclotron Laboratory
Date: 1947-2002
Object number: 2003-1-0291
Date: 1890-1930
Object number: RS0501
Sanborn Company
Date: 1930-1945
Accessories: leather cover; cloth cover; thin red wire
Object number: 1996-1-0278
Hickok Electrical Instrument Company
Date: 1955-1965
Object number: 1998-1-0879
Western Electric Company
Date: before 1933
Accessories: cords missing
Object number: RS0153
