Solenoid Fundamentals: Introduction

Introduction

A solenoid is a simple rugged device providing the interface between the electronics and mechanichals actuation in many types of equipment. Its component parts consist of a coil (to carry current and generate ampere turns), an iron shell or case (to provide a magnetic circuit), and a movable plunger or pole (to act as the working element).

A major objective in the design of a solenoid is to provide an iron path cabable of transmitting maximum magnetic flux density with a minimum energy input. Another objective is to get the best relationship between the variable ampere turns and the working flux density in the air gap. The working gaps flux density can be increased by increasing the electrical input to the coil. However as the electrical input increases the coil temperature rises and the work output is reduced. The amount by which the electrical input can be increased depends upon the relative duty cycle and maximum allowable coil temperature.

1. The magnetic flux generated is dependent on the number of turns and the current developed when power is applied to the coil. The permissible temperature rise limits the magnitude of the power input.Working flux density is the total magnetic flux divided by the magnetic path (iron path) area.
2. Many of our solenoids have an auxiliary flux path, not normally found in conventional solenoids, which provides a significant increase in force.
3. The air gap, the iron path, the pole piece and its contour determine the working flux density.