Week -2

Question 2 : Use a thermistor to sense the temperature of a heater and turn on or turn off the fan as per below.

Answer: Here we need to turn on the fan when the temperature is above 25C

The blocks used are

Signal builder: used to build the signal that we require

Controlled temperature source: Used to give the physical temperature as the input to thermistor

Thermistor: used to sense the temperature

DC voltage source: used to give the dc input to the thermistor (here dc voltage given is 100v)

Switch:used to give an output to the controlled voltage source according to the threshold value on it .

Controlled voltage source: It is turned on or off according to the controll signal applied to its port

DC motor:Here the fan is assumed as motor.

Ideal rotational sensor: used to sense the rotation of the motor and provide the output

PS-Simulink convertor: here the physical signal is converted to simulink signal

Simulink-PS convertor:here the simulink signal is converted to physical signal.

Voltage sensor:used to find the voltage

Scope : used to observe output

WORKING:

Here the signal generator provides the required simulink signal which is converted to physical sugnal simulink ps convertor and is fed to the cntrolled temperature source. The temperature is converted to kelvin in the signal builder since the temperature in controlled voltage source is in kelvin(for example 20C=273+20=293K).Likewise every temperature given is converted to kelvin.Accordingly the temperature source will produce physical temperature according to the time and will give the temperature output to the thermistor.A dc voltage source of 100v is connected to the thyristor and the output voltage will depend on the temperature since thermistor changes its resistance according to the temperature. From the scope connected to the voltage sensor we can see the voltage according to each temperature.From that voltage for the temperature 25 C is noted and is given as threshold to the switch.The switch is connected with constants 0 and 1 .The outputs are given according to the threshold value.Here the ouput will be 1 when temperature is greater than 1 and 0 when less than 1.Here the threshold is given as 0.1 since ouput voltage for the temperature 25C is 0.1.When the limit of threshold in the switch exceeds the given value the switch will provide the constant 1 as output and is given to the controlled voltage source.As a result the voltage is produced and is given to the dc motor and it will start working.The rotation and speed of motor is analysed using the ideal rotational motion sensor whose ouput is given to the scope where the ouput graph is obtained.

Graph

Here the graph is obtained through scope by running the simulation for 50 sec

Scope1: provides the output graph of voltage sensor.The threshold voltage and the voltages for each temperature is found from this graph

Scope 2: provides the output graph of motor speed.

Question No 2: Make a simulink model of door bell.

Answer: Here it is required to build a simulation of door bell and analyse the movement of the plunger of solenoid through simulation results.The blocks used are

Solenoid:used as a bell and the movement of its plunger is analysed.

Controlled voltage source: It is turned on or off according to the controll signal applied to its port

Ideal translational sensor: used to sense the translational motion of the plunger.

PS-Simulink convertor: here the physical signal is converted to simulink signal

Simulink - PS convertor:converts simulink signals to physical signals

Signal builder : used to build the signal such that amplitude is 1 for a period of 2 seconds and zero for the remaining time.

Switch:The switch used here is from simulink library and threshold value is given as one.

Scope:used to get the graphical output.

Working:

The signal builder provides the necessary signal that is an output of for a period of 2 seconds and zero for the remaining time such as a switch which is on for 2 seconds.The output of signal builder is connected to the switch (simulink library)where the threshold is set as 1 in such a way that its output is given as 100 if the input from the signal builder is greater than or equal to one otherwise it will give the output as zero.That is the switch will provide the out put as 100 during the inetrval 0 to 2 in the signal builder and otherwise it will be zero.The output of the switch is connected to the controlled voltage source where the voltage source provides a voltage according to the signal provided at its input.The input of the voltage source is given to the solenoid where the solenoid provides mechanical motion as output.The movement of plunger is analysed using translational motion sensor and is given to scope for the graphical representation.

Graph

here the initial condition is set to 0.5m so that movement in positive direction is obtained.Since the movement will be only in mm we can see from the graph that plunger starts from 0.5 mm and move till 0.495mm. some extra movements can be seen which can be removed by adjusting damping in solenoid properties and thus the result is obtained.