GALVANOMETERS

In telegraphy Galvanometers were also called detectors and usually connected on the line side of circuits, at each end.  The indicating needle would deflect to current in the line and direction of the deflection would depend on the polarity of the current received.

Because these are highly sensitive, low current instruments, a low resistance shunt is connected across the connections, so only a small portion of current passes through the detector.

The Galvanometer checks the condition of the transmitter and key, and indicates to the user, the strength of the current arriving from the distance office.

The No. 1A (graduated) and the No. 22A (non-graduated) were in general use.  The No. 1A (50ohm) being used on Duplex and Quad circuits and the No. 22A (30ohm) used on Direct and Single Current circuits.

Click here for the full Galvanometer list

Pictures

Galvanometer No. 1 (picture dated 1921)

Galvanometer No. 22A (picture dated 1902)
Located in a sounder screen and with a double plate sounder on either side