hot wire voltmeter
Datecirca 1913
Inventory Number0315
ClassificationVoltmeter
Subject
Maker
Hartmann & Braun AG
1879 - 1999
Supplier
James G. Biddle Company
fl. 1890 - 1950
Cultural Region
Place of Origin
Place of Use
Dimensions22.3 × 21.3 × 14 cm (8 3/4 × 8 3/8 × 5 1/2 in.)
Material
DescriptionA voltmeter consisting of a wooden box with a lid on front that exposes the top half of the instrument containing its scale. The scale is arc-shaped, with two different ranges (0-3 and 0-30 volts), and the distance between its marks increases slightly with the voltage. It has a reflective band underneath, and its pointer is a very thin needle.
The wooden box has three painted metal binding posts on top and a metal and bakelite handle. The inside of the lid has the instrument specifications including a schematic.
The back of the box as well as windows on the sides near the back are in perforated metal. It contains the instrument's shunts.
The wooden box has three painted metal binding posts on top and a metal and bakelite handle. The inside of the lid has the instrument specifications including a schematic.
The back of the box as well as windows on the sides near the back are in perforated metal. It contains the instrument's shunts.
Signedbelow scale: VOLTS / JAMES G. BIDDLE, PHILADELPHIA / 30 VOLTS ca 101 OHMS
Inscribedto the left of scale: No. 443760
diagram on lid marked: ORDRE 1256/13 INSTR 69244 No. 13355
on dial in German: Mit vertikaler Skalenstellung zu benutzen [translation: To be used with the scale placed vertically]
Curatorial RemarksInstrument card says "similar to Instrument No. 316" but it must be in an old numbering system as that instrument is very different; however, it is very similar in shape and operation to ammeter No. 0281 of the Collection.
FunctionThis device can measure direct and alternate voltage of any frequency. It does so by determining the power consumption through a fine wire of known resistance by measuring the increase in its length cause by the heat produced. This is translated to a voltage reading on the scale. Below is a detailed description from the original instrument's card in the museum.
"Fine wire stretched between two posts: one post under the scale. The other post at the bottom of the instrument. About the center of the wire, a thread is taken off perpendicularly, making one turn around a pulley which is on the spindle carrying the pointer. The thread is then attached to a flat spring which takes up the slack in the wire due to heating by the current. A D-shaped aluminum disc is attached to a spindle which passes between the poles of a permanent magnet for damping. All mounted on a circular bakelite disc".
"Fine wire stretched between two posts: one post under the scale. The other post at the bottom of the instrument. About the center of the wire, a thread is taken off perpendicularly, making one turn around a pulley which is on the spindle carrying the pointer. The thread is then attached to a flat spring which takes up the slack in the wire due to heating by the current. A D-shaped aluminum disc is attached to a spindle which passes between the poles of a permanent magnet for damping. All mounted on a circular bakelite disc".
ProvenanceFrom the Harvard Engineering School. Removed to the collection in 12/1956.
Richard W. Thomas
Date: circa 1861
Accessories: bottle and beaker (1998-1-1634a); hydrometer and manual (1998-1-1634b)
Object number: 1998-1-1634
Siemens & Halske AG
Date: 1897-1903
Accessories: wooden case
Object number: 0273a,b
Hartmann & Braun AG
Date: 1900-1920
Accessories: plugs (8)
Object number: 1997-1-0399