The Invention of the Track Circuit / The history of Dr. William Robinson's invention of the track circuit, the fundamental unit which made possible our present automatic block signaling and interlocking systems

by American Railway Association

THE ROBINSON CLOSED RAIL CIRCUIT.

Fig. 2.
Wm. Robinson, 1871, Patented in France, February 29, 1872, and United States August 20, 1872. Re-issued July 7, 1874. No. 5958.

The Robinson closed rail circuit, which now forms the basis, according to the best information, of every efficient automatic electric, electro-pneumatic and electrically controlled fluid pressure system throughout the world, is illustrated in its simplest form, in Fig. 2.

This figure shows the railroad track divided into sections, a mile more or less in length, the section rails being insulated from adjacent sections. A light battery has its terminals connected to the opposite rails at one end of the section and at the other end a relay magnet has its terminals connected to the opposite rails. Thus the current passes through the whole length of the section, keeping the relay on continuously closed circuit and magnetized as its normal condition. The relay thus keeps the secondary circuit, which directly controls the signal, normally closed, whereby the signal is normally held in a position indicating safety.

When a train enters upon the section, the wheels and axles, connecting the opposite rails thereof, short circuit the current from the relay, which instantly releases its armature, thus opening the signal circuit. The signal is then instantly thrown to the danger position by means of a counterbalance.

The signal may be of the enclosed disk type, electro-mechanical, electro-pneumatic, electrically controlled gas, or of any other kind. The Robinson patented system is broad, basic and a generic creation; it is not limited to any specific construction or arrangement of signal but covers all kinds.

In expounding the early history of the art of automatic signaling, the following photographic reproductions from some of Robinson's early circulars and patents will be of interest.

The following sections on Curve, Tunnel, Station, Switch and Draw-Bridge Signals are a photographic reproduction from a circular issued by Mr. Robinson in 1870:

CURVE AND TUNNEL SIGNALS.