[Illustration: Fig. 754.--Wiring diagram of the standard form of Monitor controller. A set of solenoids are connected in series and so interoperating as to cut resistance out of the armature circuit of the motor as the apparatus it is driving comes up to speed. The controller is designed to be used on all classes of work. In its simplest form, a single copper and graphite contact, is controlled by two magnets, so proportioned as to cut out the entire starting resistance when the armature current falls to a predetermined value. In the larger sizes, the number of steps controlling the resistance is increased and arranged to produce the correct acceleration. In every case the regulation of the starting resistance is effected entirely by the current passing to the motor without the use of dash pot, mechanical governor or delicate cut outs. The time element is thus directly proportioned to the load and the motor brought up to speed in the shortest time consistent with the load, but always with safe limitation of the armature current. The distinction between the current controlled starter and the starter with dash pot governor should be noted. The starter here shown limits the starting current to a fixed value throughout the starting operation, which is an ideal condition and prevents blowing fuses in starting.] Ques. How can shunt motors be controlled from a distant point? Ans. The starter and switch are placed at the desired point and the two main wires and the field wires run from that point to the motor. This requires additional wire which increases the cost and line loss. Regulation of Motor Speed.--Motors are generally run on constant voltage circuits. Under these conditions, the speed of series motors varies with the load and at light loads becomes excessive. Shunt motors run at nearly constant speeds. For many purposes, particularly for traction, and for driving tools, it is desirable to have speed regulation, so that motors running on constant voltage circuits may be made to run at different speeds. The following two methods are generally used for regulating the speed of motors operated on constant voltage circuits: 1. By inserting resistance in the armature circuit of a shunt wound motor; 2. By varying the field strength of series motors by switching sections of the field coils in or out of circuit. Ques. Describe the first method. Ans. This method is illustrated in fig. 756. When the main switch is closed, the field becomes excited, then by moving the lever P of the starting rheostat the various contacts (1, 2, 3, 4, 5), more or less of the rheostat resistance is cut out of the armature circuit, thus varying the speed correspondingly.