SOLENOID
OBJECTIVES
General objective : To apply the concept of a solenoid.
Specific objectives : At the end of the unit you should be able to:
· Identify the main function of a solenoid
· Identify the application of a solenoid
· Describe the application of solenoids with operating valves
· Draw the symbol of a solenoid with a standard symbol
· Draw a control circuit showing the energizing of a solenoid through the closing of relay contact, using a
control relay, two push- button switches and a solenoid
4.1 INTRODUCTION OF SOLENOID
The general principle of the solenoid action is very important in machine control. Solenoid is an electromechanical device. Electrical energy is used to magnetically cause mechanical movement.
4.2 PRINCIPLE OPERATION OF SOLENOID
A solenoid is a coil with an iron core and moveable iron plunger. When the coil is energized, the plunger is attracted by the coil. It “pulls in”, and this motion can be used to activate another mechanism. The solenoid shown in figure 4.2 (a), is used in many electrically activated devices such as valves, locks, punches and marking machines.
Solenoid is made up of three basic parts
a. Frame
b. Plunger.
c. Coil.
The frame and plunger are made up of laminations of high-grade silicon steel. The coil is wound of an insulated copper conductor. Solenoids for alternating current use are now available as oilimmersed types. Heat dissipation and wear conditions are improved with this design.
4.3 SYMBOL OF A SOLENOID.
4.4 TYPES OF SOLENOID.
There are many kinds of solenoids. Figure 4.4, shows one type of solenoid in industrial use.
4.5 BASIC FUNCTION OF SOLENOID CONTROL CIRCUIT
Operating the START push-button switch close the circuit to the coil of relay ICR as shown in figure 4.5(a). The coil is now energized. Relay contact 1CR-1 as shown below then closes, interlocking around the START push-button switch. Contact 1CR-2 closes, energizing solenoid A. The circuit can be de-energized by operating the REVERSE push-button switch.
In figure 4.5(b), a time-delayed relay is added. Operating the START push button switch closes the circuit to the coil of relay 1CR. The coil is now energized. Contact 1CR-1 closes, interlocking around the START push button switch. Contact 1CR-2 closes, energizing solenoid 1A. Contact 1CR-3 closes, energizing the coil of timing relay 1TR. After a time delay, as set on the timing relay, the timing constant contact closes, energizing solenoid 1B. The circuit can be de-energized by operating the REVERSE push-button switch. Note that if for some reason the REVERSE push button switch is operated before the time set on the timing relay expires, solenoid 1B will not be energized , as the timing relay coil will be de energized . With the relay coil de-energized , the timing contact remains in the normal open condition.
4.6 APPLICATION OF SOLENOIDS
Solenoids are used to control fluid flow in hydraulic or pneumatic system. Solenoids are also applied in many electrically activated devices such as valves, locks, punches and marking machines.
