reflecting galvanometer
Date: circa 1923
Inventory Number: 1997-1-0320
Classification: Reflecting Galvanometer
Subject:
Maker: Leeds & Northrup Company (1903 - 1995)
Cultural Region:
Place of Origin:
Dimensions:
22.2 × 13.1 × 13.1 cm (8 3/4 × 5 3/16 × 5 3/16 in.)
Description:
A cylindrical black brass case on moulded circular bakelite base with three levelling screws and two binding posts on base. The cylinder has a long, narrow, rectangular glass window. Behind the window is a small circular mirror suspended from a thin wire above and connected to a metal cylinder below, which lies at the center of a cavity between the poles of a magnet. Attached to the top of the magnet is the structure that supports the wire, which includes a zero adjustment screw and a screw that adjusts the clamp system for locking the coil when not in use. Both the zero adjustment and the coil clamp use the same removable knurled brass knob. There is an additional knob projecting from the side of the case for making the final zero adjustment.
Signedon base between binding posts: LEEDS & NORTHRUP CO. / PHILADELPHIA PA
Inscribedon underside of base (serial number): 184789; on top of case, MADE IN U.S.A.; on base, painted: E 1011 / H.E.B. C.R.F.
FunctionReflecting galvanometers are used to measure very small electrical currents and voltage differences. Instead of having a scale with a pointer, in these galvanometers a small mirror turns in the presence of electrical currents. The change of angle can be detected by shining a light at the mirror and observing the reflection on a large scale that is placed in front of the device. Alternatively, a scope is pointed at the mirror to see the change in the angle that the scope points to on a scale seen through the mirror. In those cases, the scales that are used are mirror-inverted.