Week -2

1.Simulation of doorbell with solenoid:

A solenoid is a type of electromagnet, the purpose of which is to generate a controlled magnetic field through a coil wound into a tightly packed helix. The coil can be arranged to produce a uniform magnetic field in a volume of space when an electric current is passed through it.

Using the solenoid,we are going to simulate a doorbell which will operate when the plunger in the solenoid is excited .

The above model is used for the simulation of a doorbell.The blocks used are,

1.Pulse generator

2.Switch

3.Battery

4.Solenoid

5.Translational motion sensor

6.Scope

Working:

• The R port will be the moving port which will be displaced to ring the bell.So a ideal translational motion sensor is placed to obtain the displacement value and given a scope to visualize the result.
• The c port is connected to the mechanical referance.
• The signal generator is used to produced the triggering signal to the switch block.
• The signal generator is set according to the requirement of the question as ON for 2s and OFF for remaining seconds.
• So the threshold value of switch is set according to the pulse generator.
• The simulation is ran for 10s.So during the first 2s the switch will be on and the plunger will move and hit the bell.
• For the remaining 8s the switch is open and the plunger will not move.

This is the output of the above simulated model.The osillation in the motion of the plunger is due to the damping constant of the solenoid .If we increase the damping constant we can get the smooth operation.

When we double click on the solenoid block we can get the properties of the solenoid ,In the mchanical tab we can change the damping value.We have to increase the damping value to get smooth response.

Thus after increasing the damping value we get the smooth response of the plunger.It is on for the first 2s and remain off for the next set of period.

2.Temperature controlled fan:

In this model we are going to sense the temperature value of a heater using thermistor and to turn on the fan when the temperature exceeds the threshold value.

A thermistor is a resistance thermometer, or a resistor whose resistance is dependent on temperature. The term is a combination of “thermal” and “resistor”. It is made of metallic oxides, pressed into a bead, disk, or cylindrical shape and then encapsulated with an impermeable material such as epoxy or glass.

The above model is used to sense the temperature and used to turn on the motor.The components used are,

1.Signal builder

2.Controlled temperature source

3.Thermister

4.Battery

5.Current sensor

6.DC motor

7.Ideal torque sensor

8.Scope

Working:

• The termistor block has 3 ports.The +,- are connected to the battery along with a current sensor block to measure the current across the termister.
• The A port is used to get the temperature signal.It is given from the signal builder which is used to create signal manually.Here the signal is created accondin to the question.
• Due to the variation in the temperature produced from the signal builder the temperature source will produuce differant values to the termister.
• The change in value to termister will result in varying current which is measured using the current sensor and the threshold value of current is find from the values.
• The threshold value of current is given to the switch to operate at the required condition.
• The switch is connected with motor along with battery.
• So when the switch gets the value greater than the threshold value ,it will close the motor start to rotate,the rotation is confirmed by the ideal torque sensor.
• If the value is less than the threshold value then the switch is off and the motor is off.

The simulation is ran for 50s according to the question,

The above graph gives the current value across the termister.The signal buillder will provide 293K for first 10s and 300K for next 20s and 296K for next 20s.For that input the current is produced as shown above.

From the above graph we can define the threshold value as 0.02 as we need to on the fan only when the temperature is above 25C(300K).

The above graph is the output of our simulation.From the graph we can definitely say that when the temperature is greater than 300K then the motor starts to rotate or else the motor remains in off state.