A face plate/drum type controller is used for starting the series motor. This controller can also be used to control the speed of a series motor as well as to reverse the direction of its rotation. It is commonly known as Series motor starter.
As the operator has to monitor the operation of motor continuously, It does not not need any safety interlocks apart except an overload protection in a series motor starter.
As we can see in the above figure, the control handle contains three different segments which are separated by an insulating material. The external resistance can be easily increased or decreased from the circuit by adjusting the control handle. Reversal of the direction of rotation of motor can be achieved by turning the control handle in opposite side. It is because in this process the armature connections are reversed.
Series motor starters are used where high torque is required to lift heavy loads like cranes, hoists etc.
When variable speed is required, it is always better to use drum controller. It is named as drum controller because it does not only controls the speed of the motor, but also controls the direction of the rotation of motor. When the control handle of the starter is moved , it gradually increases or decreases the external resistance applied to the armature circuit and hence controls the speed of the series motor. However, if you turn the control handle in opposite direction, the direction of rotation of the series motor is reversed. The various safety protections like open circuit protection and over current protections can also be applied to series motor starter in addition.