hot wire ammeter
Datecirca 1925
Inventory Number0425
ClassificationAmmeter
Subject
Maker
General Radio Company
1915-present
User
Radiation Laboratory of the Massachusetts Institute of Technology
1940 - 1945
Cultural Region
Place of Origin
Dimensions13.9 × 12.7 × 9 cm (5 1/2 × 5 × 3 9/16 in.)
Material
DescriptionHot wire ammeter consisting of a small rectangular wood case with the lid screwed down and a leather carrying handle on top.
There is a fan-shaped opening with a glass cover over the scale, as well as binding posts and a set knob. The nonlinear paper scale is hand-calibrated and runs from 0-3, with a cramped space in the first interval between 0 and 0.5.
There is a fan-shaped opening with a glass cover over the scale, as well as binding posts and a set knob. The nonlinear paper scale is hand-calibrated and runs from 0-3, with a cramped space in the first interval between 0 and 0.5.
Signedon face: GENERAL RADIO CO. / MODEL 170
FunctionFrom original museum card: "Designed by Melville Eastham of the General Radio Co in 1925 and used by the Cruft in RF [radio frequency] experiments in Students Lab."
This 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".
This 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".
ProvenanceFrom the Department of Physics, Cruft Student's laboratory, Harvard University.
General Electric Company
Date: 1940-1970
Accessories: leather case
Object number: 1997-1-1085
