Stator flux linkage is estimated by integrating the stator voltages. The rotating magnetic field induces an AC voltage in the stator windings. Electric motors generate internal magnetic fields to rotate the rotor in the stator. Progressive cavity pumps consist of a single helix rotor inserted into a double helix stator. Synchronous reluctance motors have an equal number of stator and rotor poles. The SRM has wound field coils as in a DC motor for the stator windings. A second arrangement has the rotor winding basket surrounding the stator magnets. The rotor is now positioned at the stator poles b. The armature can be on either the rotor or the stator. The main components of the motor are the stator and rotor. Most larger DC motors are of the "dynamo" type, which have stator windings. The rotor of one motor is connected to the stator of the other. The PCP consists of a stator and a rotor. The distance between the rotor and stator is called the air gap. This produces greater pressure rise per stage which constitutes a stator and a rotor together.