hot wire ammeter
Date1910-1930
Inventory Number0281
ClassificationAmmeter
Subject
Maker
Hartmann & Braun AG
1879 - 1999
Supplier
James G. Biddle Company
fl. 1890 - 1950
Cultural Region
Place of Origin
Dimensions23 × 21 × 10 cm (9 1/16 × 8 1/4 × 3 15/16 in.)
Material
DescriptionAn ammeter 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 (0-2 and 0-0.5 amps), and the distance between its marks increasing slightly as the current increases. It has a reflective band underneath and its pointer is a very thin needle.
The wooden box has five metal binding posts on top and a metal and bakelite handle. The inside of the lid has the instrument specifications including a schematic. According to it, the instrument has a third range of 0-1 amp although it is not marked in the scale.
The wooden box has five metal binding posts on top and a metal and bakelite handle. The inside of the lid has the instrument specifications including a schematic. According to it, the instrument has a third range of 0-1 amp although it is not marked in the scale.
Signedbelow dial: AMP. / JAMES G. BIDDLE, PHILADELPHIA / MADE IN GERMANY
Inscribedto the left of scale: No. 442077
inside of lid numbered: 69248
stamped on bottom right of instrument: 281
inside of box stamped: 99
above scale: For use the dial must be in vertical position
Curatorial RemarksThis ammeter is very similar in shape and operation to voltmeter with inventory number 0315 of this Collection.
FunctionThis device can measure direct and alternate current 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 an amperage reading on the scale.
Below is a detailed description from the instrument card of a very similar device in the collection (No. 0315):
"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".
Below is a detailed description from the instrument card of a very similar device in the collection (No. 0315):
"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 this collection in 11/1956.
Weston Electrical Instrument Corporation
Date: circa 1913
Object number: 1997-1-0328
Weston Electrical Instrument Corporation
Date: circa 1922
Accessories: standardization certificate from 1922 inside lid
Object number: 1997-1-0337
Harrison Laboratories Inc.
Date: mid 20th-late 20th Century
Accessories: Red and black patch cords, still plugged into front of unit.
Object number: 2004-1-0416
