22 MANUAL OF CURRENT OBSERVATIONS 
56. Special attention must be given to the contact chamber, as this is the most 
common source of trouble in the operation of the meter. The contact springs are very 
slender and a slight bending or misplacement might result either in a continuous contact 
or failure to make contact. The operation should be checked from time to time by 
removing the cap on the contact chamber and noting whether definite contacts are 
made as the meter wheel is rotated and also whether there is sufficient clearance to avoid 
any grounding of the current between the normal contacts. When the meter is in use, 
the contact chamber should be kept filled with light or medium oil to prevent any salt 
water from attacking the contact points. This does not appreciably affect the rating 
of the meter and experience has proven its value. 
57. To locate the cause of a failure in the electric circuit that is not immediately 
obvious, proceed as follows: First test the battery and earphone in a circuit and note 
whether distinct clicks are heard when the circuit is made and broken at one of the 
battery terminals. If no clicks are heard, try a new battery and, if necessary, another 
earphone. If both battery. and earphone are in good operating condition, introduce 
the meter into the circuit; connect one wire to the yoke of the instrument and the other 
wire successively to each of the contact plugs in the contact chamber. In this case 
the circuit may be made and broken by rotating the cup shaft of the meter. If the 
meter is all right, a click will be heard for each turn of the cup shaft when connection 
is with the upper contact plug, or for each 5 turns when connection is with the lower 
contact plug. If the meter is found to be operating satisfactorily, the electric wires 
of the meter cable should be placed in a circuit with the battery and earphone and the 
circuit made and broken by bringing together the ends of the two cable wires. If no 
clicks are heard, the cable should be carefully examined for any break in either of the 
copper wires. Such a break is most likely to be found near either end of the cable or 
at a point known to have received an exceptionally sharp bend. When in use it is 
recommended that waterproof grease be applied to the terminals of the cable at the 
connections with the meter as a precaution against the shorting of the current through 
the frame of the instrument, especially when operating in deep water. If the signals 
are inclined to be weak, it is advisable to wrap the bare cable terminals and contact 
plugs with waterproof tape before applying the grease. 
58. The suspension of the meter on a metal stem attached to the supporting cable 
is designed so that the axis of the meter can move vertically as well as horizontally 
in order to keep parallel with the direction of the current. Before being placed in 
the water the vertical movement should be checked and the balance weight on the tail 
vane adjusted to eliminate any tendency to tip in either direction. 
59. Automatic recording device.—An automatic recording device for use with the 
Price current meter, which was developed by the United States Engineers, is described 
in an article entitled ‘(Measuring Currents in New York Harbor,” by Harold E. Libby, 
published in the Military Engineer for September—October 1932. The device (fig. 16) 
replaces the earphone and consists of an electric accumulator relay and a recorder. 
An operating battery of about 3 volts is in one circuit with the current meter and the 
electro-magnet of the relay, and in another circuit with an electro-magnet in the 
recorder, the latter-circuit being opened and closed by the action of the relay. 
60. The recorder contains a circular time chart about 10 inches in diameter which 
is rotated by clockwork and a recording pen operated by an electro-magnet. With | 
the electric circuit open, the pen traces the circumference of a circle about 8 inches in 
diameter, but each time the circuit is closed, a short outward stroke is made through 
the action of the electro-magnet on the pen arm. The frequency of these contact 
