Permanent Magnet Moving Coil Relay:
The arrangement of permanent magnet moving coil relay is shown in Fig. 9.12. In this relay, the coil is free to rotate in the magnetic field of a permanent magnet. The torque is developed by the interaction between the field of the permanent magnet and the coil field developed due to flow of actuating current in the coil. The time-current characteristic of such relays is an inverse-time characteristic. The relay responds to dc only but it can be used with ac in conjunction with a rectifier. The characteristic can be varied by adjusting the control spring. The time setting is obtained by adjusting the position of the contact.
The operating torque is proportional to the actuating current. Such a relay has uniform torque for different positions of the coil and therefore, can be accurately set. Theoretically the reset value is equal to the operating value.
Moving Coil Relay With Axial Moving Coil
Moving Coil Relay With Axial Moving Coil is shown in Fig. 9.13. The coil is supported axially and moves horizontally when energized by the actuating current. Such relay is faster than the rotating coil type owing to small travel and lighter parts. Relay of this type may have an operating time of the order of 0.03 second. Sensitivity can be made as small as 0.1 mW. These relays are delicate and so require careful handling.
