Before starting a motor--starting a motor--various starting resistances--starting boxes--speed regulators--Cutler Hammer starter--time required to start motor--how to start--sliding contact starters--series motors on battery circuits--starting a shunt motor--multiple switch starters--effect of reverse voltage--rheostat with no voltage and overload release--failure to start--starting panel--Cutler Hammer starting rheostats--Allen Bradley automatic starter--Monitor starter with relay for push button control--a remote control of shunt motors--regulation of motor speed; various methods--Monitor printing press controller--speed regulation of series motor, by short circuiting sections of the field winding--varying the speed of shunt and compound motors--Cutler Hammer multiple switch starter--regulation by armature resistance--Compound starter--regulation by shunt field resistance--Holzer Cabot instructions for shunt wound motor--Reliance adjustable speed motor--Cutler Hammer reversible starter--combined armature and shunt field control--selection of starters and regulators--Watson commutators--organ blower speed regulator--General Electric controller--speed regulation of traction motors--controller of the Rauch and Lang electric vehicles--two motor regulation--controller connection diagrams--stopping a motor.
CHAPTER XXVI
GALVANOMETERS
If a compass needle be allowed to come to rest in its natural position, and a current of electricity be passed through a wire just over it from north to south, the north seeking end of the needle will be deflected toward the east. If the wire be placed under the needle and the current continued from north to south the needle will be deflected toward the west. Again, if the current be passed from north to south over the needle, and back from south to north under the needle, as shown in [fig. 504], the magnetic effect will be doubled, and the needle deflected proportionately. Upon these phenomena depend the working of galvanometers.
Fig. 503.--Effect of neighboring current upon a magnetic needle. Above the needle and parallel to it is a conductor carrying an electric current, the current flowing in the direction indicated by the arrow. This causes the north pole of the needle to turn toward the east. If the conductor be held below the needle, its north pole will turn in the opposite direction or toward the west. These movements are easily determined by Ampere's rule as follows: If a man could swim in the conductor with the current, and turn to face the needle, then the north pole of the needle will be deflected toward his left hand.
Ques. Describe a simple galvanometer.
Ans. It consists essentially of a magnetic needle suspended within a coil of wire, and free to swing over the face of a graduated dial.
Ques. What is a galvanoscope and how does it differ from a galvanometer?
Ans. A galvanoscope, as shown in [fig. 504], serves merely to indicate the presence of an electric current without measuring its strength. It is an indicator of currents where the movement of the needle shows the direction of the current, and indicates whether it is a strong or a weak one. When the value of the readings has been determined by experiment or calculation any galvanoscope becomes a galvanometer.