TYPES OF INDICATORS
2. Column Indicators.—A very simple indicator, and one that was formerly very commonly used, is made by inserting a pin into the center of the end of the drum shaft and using this as a miniature drum on which to wind and unwind a chain or cord, which corresponds to the hoisting rope as the pin corresponds to the drum. This chain or cord is led over a pulley placed at the top of a pair of guides, representing the shaft, and carries at its end a weight, pointer, or gong, representing the cage or car, as shown in [Fig. 1].
Fig. 1
Fig. 2
The different landings in the shaft are marked on the guide; and as the pointer or gong rises and falls it indicates the position of the cage in the shaft. If a gong is used, pointer also may be added and the gong so arranged that it will ring at a point some distance before the landing is reached and thus attract the engineer’s attention. Indicators of this kind, though cheap and easily constructed, are not reliable, for the cord and chain may stretch or they may overlap in winding on the pin, or may bind in the pulley and thus indicate a wrong position of the cage.
3. An indicator should have a positive motion and be driven by gearing or by link belts. [Fig. 2] shows a column indicator that consists of a screw a working inside of a slotted pipe b, which may be of any length necessary. This screw is revolved by means of the gears c, which are rotated by the sprocket wheel d. A nut e travels up and down the screw a and the pointer f attached to the nut indicates the position of the cage in the shaft. The pipe standard b is usually painted a dead black and the different levels may be marked on it with chalk or white paint. Chalk marks are not safe, as they may be tampered with and the engineer thus misled.
Fig. 3