Week -2

AIM

• To make a simulink model of door bell using solenoid block
• To make a simulink model using thermistor to sense the temperature of heater and turn on or turn off the fan

THEORY

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 tight 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 . The term is often used to refer to a solenoid valve an integrated device containing an electromechanical solenoid which actuates either pnuematic or hydralic valve or a solenoid switch which is specific type of relay that internally uses an electromechanical solenoid to operate an electrical switch for example an automobile starter solenoid or linear solenoid . Solenoid bolts a type of electromechanical locking mechanism also exist. In electro magnetic technology a solenoid is an actuator assemly witha sliding magneic plunger inside the coil . Without power the plunger extends for a part of its length outside the coil applying power pulls the plunger into coil . Electromagnets with fixed cores are not considered solenoids.

THERMISTOR

A Thermistor is a type of resistor whose resistance is dependent on temperature more so than in standard resistors. The word is a combination of thermal and resistor. Thermistors sre widely used as inrush current limiters temperature sensors self resetting overcurrent protectors and self regulating heating elements .

Thermistors differ from resistance temperature detectors in that the material used in a thermistor is generally ceramic . While RTDs use pure metals . The temperature response is also different RTDs are useful over larger temperature ranges while thermistors typically achieve a greater precision within a limited temperature range .

OBJECTIVES

For Door Bell

Create a situation where the switch is closed for 2 seconds and then released . Observe the physical movement of the plunger

For FAN

Temperature source should be 20 c from the 0 to 10 seconds , 27 c from 10 to 30 seconds , 23 c from 30 to 50 seconds . Fan condition should be on if the temperature above 25 c off otherwise

SIMULINK MODEL

DOOR BELL

• From the above governig circuit a door bell we know that we need switch, solenoid , battery , plunger.
• In order to get all these components into simulink model we have to taken blocks that perform same action what the above devices perform.
• Solenoid block is taken to represent a solenoid in the model then to represent the battery we have taken battery block from the library browser.
• Then this solenoid block and battery block are connected to each other via positive and negative terminals.
• Switch block is placed between solenoid block and battery block and its is connected with the blocks.
• Now this whole battery switch and solenoid path is connected to an Electrical Reference Block which represents earthing circuit .
• Then the solenoid block R and C are two variables which represents plunger and fixed point respectively.
• Now this R is connected to a R ideal translational motion sensor block which senses the position of the plunger in the solenoid block and gives the output.
• Now C in the ideal translation motion sensor block is a mechanical translation conserving port which means that the mechanical process starts from R and Ends at C
• Now to provide a physical signal for operating the switch we have used a pulse generator block which generates a contionous square pulse.
• From Starting to ending of the pulse it will take 4 secs of time periods in which only for 2 secs the amplitude will be one and for rest of time it will be zero So after these 4 secs the cycle continues
• To this pulse generator block Scope block is connected to see how pulse is generated.

OUTPUTS

• The above figure obtained by running simulink model clicking on scope block. This figure shows how the pulse generated and this figure x axis represents the time and y axis represent amplitude
• Thus represents that we when amplitude is one the switch will be closed and when it is zero switch will open. Since our objective is only to see the change in position of plunger when switch closed for 2 secs so that we have amplitude 1 for 2 secs in the pulse generator by making pulse width half

• We will get above graph as the result when we double click on the scope block . Here x axis represents the time in seconds and y axis represents position of plunger in mm
• Again the amplitude of the pulse becomes zero the plunger returns to its intial position back again and as the pulse cycle goes on plunger also changes its position and comes back to its intial position
• We can observe that when there is a change in position of the plunger there some waves forms at the start of change sin positon . This is due to recoil of the spring each time when plunger is moving so that reduce this in the solenoid block we can reduce the spring constant value and increase the damping coefficient . This will reduce the waves that are being formed and we will get asmooth graph

FOR FAN OPERATION USING THERMISTOR

• To create a simple cooling fan model using thermistor we nee da thermistor , battery , resistor, voltmeter a logical switch which are basic components of the circuit we need in the simulink model
• First to represent a thermistor a Thermistor block is taken and placed in the model . Now to represent a battery a battery block as taken and the positive part of this block is connected to positive part of the thermistor block
• Now represent the a voltameter a Voltage sensor Block is connected parallel to the resistor block because to measure voltage across a component voltameter should be always connected parallel to that component
• Thus we have completed our simple circuit model but we need some physical quantites to as signal as the thermistor to work
• Now to give different temperatures to this Controlled temperature source block we need to send temperature signal.To send these signals we have used as signal builder block which only gives a specified temperature as output even through heat flow
• We have to double click in the single builder block set to signal according to our requirement

OUTPUT

• From the above figure we can see that how voltage is changing with change in temperature . Using this information we set conditions for fan to on and off
• If we observe the graph we notice that from time 0 to 10 seconds when temperature is 293k volatage is between 0.0095 and 0.01 and from 10to 30 seconds when temperature is 300k voltage is between 0.0125 and 0.013 from 30 to 50seconds when temperature is 296k voltage is nearly 0.011
• As mentioned in the objective fan should be on when the temperature is the more than 25 degree celsius from the above graph when voltage is the more than 0.011 the fan should on and when voltage is below 0.011 fan should be off
• To set the threshold value value of switch block we have to doule click on the switch block and then we can change the value threshold . Since we want switch be on only when the tempearture is 300 k so that threshold is given as 0.011 . So when voltage gets more than 0.011 the switch will give value 1 as output which means fan will be on and when voltage gets less than 0.011 the switch will give value 0 as output which means fan will be off
• Now the output of switch block is connected to another spoce block to get results

• By Double clicking the scope block we can observe the above graph here we can clearily see that when temperature is 300k the fan is on and at remaining temperature the fan is off

CONCLUSION

• The both objectives are achieved sucessfully
• Similar approach can be used for simulating other physical devices using simulink

LINKS

https://drive.google.com/file/d/1q6nMYeu-PQIVisTexhxdUZNzRDyJKZvK/view?usp=sharing

https://drive.google.com/file/d/1reZU7SXafshHZcMg2Z1aGxG_KPl-sg50/view?usp=sharing