MAKING A CIRCUIT USING A RELAY

1. INTRODUCTION
   An electromagnetic relay in its switching principle is a mechanical switch which is operated with a low-power DC voltage. The switch part is used to control high power circuits.
2. SPDT RelayRelay design
                 The SPDT relay is mainly made up of :1. Movable armature
   2. Control coil
   3. Switch contact points
   4. Coil terminals
   5. Common terminal

   Description

   RELAY SPDT (single pole double throw) has a total of five terminals Out of these two are the coil terminals. A common terminal is also included which connects to either of two others. When a voltage is applied to the control circuit, the coil traversed by a current will create an electromagnetic field; this latter is capable of moving a metal element called movable armature.

3. Experimentation*.Objective:
   Make circuit by using a relay in the DCAClab simulator.*. Equipment:
   • Battery (Electromotive Force E = 1.5 v , Internal resistance r = 1 Ω)
   • Switch K₁
   • Coil (r1 = 1Ω)
   • Relay Switch
   • Lamp (r₂ = 1Ω)
   • Fan

*. Experiment 1: order a single circuit

• Experimental mounting
  
• Interpretation
  • Level 1
    1^st case: Relay at rest
    The switch K₁ open ( I₁ = 0  ) ⇒K₂ at the position (1), consequently  the circuit B is open : I₂ = O , so the lamp L is off .
    2^nd case: Relay at work
    The switch K₁ is closed ( I₁ ≠ 0 )⇒K₂ at the position (2), consequently  the circuit B is close : I₂ ≠ 0 , so the lamp L is on .
  • Level 2_ calculating the intensity of the current I₁:Ohm’s law: Ue₁ = r₁ I₁ = E – r I₁
    So  I₁  = E/ (r1  + r)  = 0.04838A ≈ 48.38 mA

     

    _ calculating the power P₁:

    P₁ = E I₁ = 1.5 x 0.04838 = 0.07257 w

    _ Value of the intensity I₂:

    By using the characteristics of the lamp we find I₂ = 1.456 A

    _ calculating the power P₂:

    P₂ = E I₂ = 1.5 x 1.456 = 2.184 w

    Conclusion:

    The relay can be used to control a high power circuit by a low power circuit.

• Experimental verification using the DCAClab simulator
  

*. Experiment 2 : order 2 circuits 

• Experimental mounting1^st case: Relay at restThe switch K1 is open ⇒K2 at the position (1), consequently:
  • The circuit B is closed, so the lamp is on.
  • The circuit C is open, so the fan is off.
• Experimental verification using the DCAClab simulator
  
  2^nd case : Relay at workThe switch K₁ is closed⇒K2 at the position (2) , consequently  :
  • The circuit B is open, so the lamp is off.
  • The circuit C is closed, so the fan is on.
• Experimental verification using the DCAClab simulator
  

the end.