Design of Electric bell and Thermistor for temperature heater using Simulink software

AIM:

To design a doorbell with solenoid block using simulink model.

OBJECTIVE:

The main objective is to design a doorbell and observe the physical movement of the plunger for t=2s.

THEORY:

A solenoid is a device consist of coil of wire, housing and moveable hammer (plunger).When the electric current passes a magnetic field is generated around the coil and making the movement of plunger upfront.

WORKING OF ELECTRIC BELL:

1. Initially the switch is open. The electromagnet is not charged as no current pass through it.The one of the battery terminal is connected to electromagnet and other is connected to contact screw which is connected the spring loaded arm.
2. When the switch is closed at t=2s.The current flows through electromagnet as it is charged and produces a magnetic field.
3. The spring loaded arm made up of iron strip.The plunger is attached to the spring loaded arm.
4. As the electromagnet gets charged it attracts the spring loaded arm which makes the plunger to hit the gong and produces sound.
5. As the plunger hit the gong, the spring arm loses its contact with the contact screw and causes the electromagnet to lose its magnetic field.
6. The spring arm moves to its original position.The contact is restored and current flowing through the circuit.
7. The process continues again.

SIMULINK MODEL:

PULSE GENERATOR OUTPUT:

DISPLACEMENT OUTPUT:

To get smooth displacement output decrease the stiffness and damper coefficient of solenoid .i.e K=100, C=5.

VELOCITY OUTPUT:

RESULT:

Thus the design of doorbell with solenoid block using simulink model is done successfully.

AIM:

To sense the temperature of heater using thermistor and turn on and turn off the fan.

OBJECTI VE:

To sense the temperature of heater for the given condition:

Temperature source: 20⁰C from 0-10 sec

27⁰C from 10-30 sec

23⁰C from 30-50 sec

Fan condition : ON if temperature is above 25⁰C ,OFF otherwise

THEORY:

The Thermistor is solid state temperature sensitive device which act bit like a electrical resistor but is temperature sensitive. The thermal resistance varies with respect to temperature.It is cheap,precise and robost.There are two types of thermistor.

NEGATIVE TEMPERATURE COEFFICIENT(NTC):

In NTC, the temperature increases resistance decreases.

POSITIVE TEMPERATURE COEFFICIENT(PTC):

In PTC ,the temperature decreases resistance decreases.

WORKING PRINCIPLE:

The principle of thermistor is that its resistance depends upon the temperature.The resistance of the thermistor is measured using ohmmeter. If we know the changes that occur between the resistance and temperature by using ohmmeter the thermistor resistance can be measured so that the value of temperature can be easily found.

SIMULINK MODEL:

SIGNAL BUILDER:

• In this module we use signal builder as input.The temperature of the heater is specified using signal builder block.
• The output of the signal builder is connected to the controlled temperature source through Simulink to PS converter where it converts the simulink signal into physical signal.
• The function of Controlled Temperature source is to maintain the temperature difference regardless of the heat flow.
• The output of the controlled temperature source is given as input to the thermistor.
• The voltage source of 12V is given inorder to run the thermistor.The resistance is connected in series with the thermistor and voltage sensor is connected in parallel.
• The voltage sensor and resistance connection is used for finding the Threshold value which is triggering value to make the fan ON/OFF.The given condition is 25⁰C.
• The Threshold value is 0.01101. The Threshold value is given as input to the switch.
• We use DC motor as fan as it converts the electrical energy into mechanical energy(motion).
• The DC motor is connected to the controlled voltage source and rotating part is connected to the ideal rotational motion sensor.The output can be viewed in scope.

VELOCITY OUTPUT:

By making constant 0 and 1 we can turn ON/OFF the fan

• For time 0-10 sec temperature is 20⁰C constant 0 i.e fan is OFF
• For time 10-30sec temperature is 27⁰C constant 1 i.e fan is ON
• For time 30-50 sec temperature is 23⁰C constant 0 i.e fan is OFF DISPLACEMENT OUTPUT:
  

RESULT:

Thus the design of thermistor to sense the temperature of heater and turn on/off fan using simulink is done successfully.