Week -2

AIM: 1) To make a Simulink model of doorbell using a solenoid block.

        2) To build a model using a thermistor to sense the temperature.

OBJECTIVE: 1) To make a Simulink doorbell model using a solenoid block with a situation of 2-sec halt & then continued further to observe the physical movement of the plunger.

                  2) To build a model using a thermistor to sense the temperature of a heater & turn on or off the fan as per conditions mentioned in the problem for the Simulink model.

OPERATING CONDITIONS:

A) For Door Bell model:-

The switch is closed for 2 seconds and then released. 

B) For the Thermistor model:-

Temperature source: 20 °C from 0 to 10 seconds, 27 °C from 10 to 30 seconds, 23 °C from 30 to 50 seconds.

Fan conditions: ON if the temperature above 25 °C, OFF otherwise.

1) DOORBELL MODEL:

                                           Fig1: Doorbell

                      Here, Doorbell consists of the main parts which include a solenoid, battery as a source, switch & bell. Here, the important part is the Solenoid on which the working of the plunger i.e movement depends. A solenoid is just an electromagnet where the coiled wire surrounds a metal piston. The piston contains magnetically conductive metal, so it can be moved backward or forward by the electromagnetic field. A magnetic field is produced here with the help of battery source. 

SIMULINK MODEL:-

Working:-

1) Here we use a pulse generator for the input condition given in the question.

2) To pass the input signal from the Simulink block to the simscape block through the switch, a Simulink to PS converter block is used.

3) The input signal is provided to a switch. A battery is connected to a solenoid to generate the magnetic field for movement of the plunger and the switch with electrical reference as a ground.

4) To track the position of the plunger, a Translational motion sensor is used. The output of the solenoid block from connector R is given to the motion sensor as an input which will ultimately give an output of position that can be observed in the graph through the scope block.

5) Translational Reference block is used for fixed point and also solver configuration is provided to solve the model with simscape block. In addition, the display block is applied which shows the output for the last value.

INPUTS:

Also stop time used is 10 seconds.

OUTPUTS:

1)

:- Here graph is obtained at the default value setting of the solenoid block in the below figure.

2)

:- Here, the value of damping is changed which is eliminating the excessive oscillations and vibrations for smooth signal intensity. 

                     According to the above example of the output, we can change the various input parameters to get the output with smooth intensity signal. For Ex: we can change the spring constant , plunger mass, etc according to the conditions for the desired output.

Result:

                     Here we run the model for 10 sec as it is a stop time provided here. The graph is obtained  for 10 seconds. From the graph, it can be seen that due to the delay of 2 sec at the initial stage, the position of the plunger is at 0. But after that, for the next 2 seconds, the solenoid will engage and there will be movement of the plunger. Again for the next 2 sec, the position will come to 0 and for the next 2 seconds plunger will show displacement. This process continues for a total of 10 seconds according to the stop time provided. 

2) THERMISTOR MODEL:

                                                               Fig2: Thermistors

                     A thermistor is a resistance thermometer or a resistor whose resistance is dependent on temperature. The term is a combination of “thermal” and “resistor”.                  

                     There are two types of thermistors: Negative Temperature Coefficient (NTC) and Positive Temperature Coefficient (PTC). With an NTC thermistor, when the temperature increases, resistance decreases. Conversely, when the temperature decreases, resistance increases. This type of thermistor is used the most.

                     A PTC thermistor works a little differently. When temperature increases, the resistance increases, and when temperature decreases, resistance decreases. This type of thermistor is generally used as a fuse.

SIMULINK MODEL:

WORKING:

1) Here NTC thermistor is used as temperature sensors to sense the temperature change of the heater & turn on or turn off the fan. 

2) To satisfy the given conditions of temperature range, here repeating sequence block is used with a sample time of 10 sec giving required temperature values. As this block is a Simulink block, hence Simulink to PS converter block is used to convert and provide the physical signal to a thermistor through a temperature source.

3) As the thermistor uses resistance for temperature sensing, a resistor is connected in series with the thermistor and voltage is measure across the resistor by connecting the voltage sensor parallel with the resistor. Also, the battery is connected as an electric source provided with reference.

4) First of all, the constant output of the voltage sensor for a temp of 298 K (`25^0 C`) is measured which is a threshold value given to the switch as an 'if' condition for the fan to turn ON or OFF. Here input temperatures that we have designed will compare their respective values with the standard value for greater than equal to or less than to the value of 298 K and activate the switch accordingly. Here constant threshold value for 298 K is noted as 0.01189 V.

So as in actual practice, when the temperature signal provided at the thermistor is greater than 298 K, its resistance decreases, and the voltage will increase than 0.01189V and vise versa.

5) Now switch has 3 inputs. We will provide the above threshold value to the middle port. Two constant blocks with values 1 and 0 are connected to turn a switch ON or OFF respectively. If the switch condition is satisfied then the signal will pass to the DC motor with the switch ON using a constant block with value 1 otherwise switch will remain OFF using a constant block with a value of 0.

6) Now, when the condition of ON will satisfy, the signal will pass through the controlled voltage source to the DC motor and it will turn on which will give angular velocity that can be observed at the end in the graph through the scope.

7) Different 'Reference blocks' for a fixed reference point and 'solver configuration' blocks to solve the simscape model are provided wherever necessary.

INPUTS:

OUTPUTS:

RESULTS:

From the above graph, it can be seen that the fan shows zero angular velocity for the first 10 seconds which is because fan is in OFF condition when the temperature is 293 K. i.e for 20 degree Celcius.

When the temp is 300 K i.e. 27-degree Celcius between 10 to 30 seconds , it is observed that the angular velocity is increased as the fan is moving. 

And when the temperature is 296 K i.e. 23 degree Celsius between the 30 to 50 seconds, we can see that the fan is again stopped as the angular velocity is decreased which will remain constant from 30 to 50 seconds.

CONCLUSION:

1) For the Doorbell model, from the graph, it can be concluded that the situation for 2 seconds delay is satisfied and the plunger movement is also observed.

2) For the Thermistor model, from the angular velocity graph, we can conclude that the fan is in motion only when the thermistor will sense the temperature greater than that of the 25-degree Celcius which satisfies the required conditions.