Week -2
Aim :
1. To make Simulink model for a doorbell using solenoid block.
2. To use thermistor to sense temperature of a heater and turn on/off the fan.
1. DOORBELL :
Make a simulink model of doorbell using solenoid block.
Simulink model explanation :
We have used following blocks in the model -
1. Pulse Generator.
2. Switch.
3. Battery.
4. Solenoiid.
5. Ideal Translational motor sensor.
6. Mechanical translational reference.
7. Electrical reference.
8. Scope.
As per given conditions switch is closed for 2 seconds and then released.
The pulse generator is used to create square wave pulses at regular intervals. The block waveform parameters, amplitude,pulse width,period and phase delay, determine shape of the waveform.
switch block is controlled by external physical signals and if the external physical signal is greater than the switch is closed or else switch is open.
positive terminal is connected to the block while as, the negative terminal is conneted to electrical reference. When we connect solenoid block with the switch and battery we form a complete electrical circuit.
The port is connected with mechanical reference. The ideal translational sensor is connected with a solenoid block R to observe the movement of the plunger. Scope is connected with the ideal translational sensor to get output.
the Position of the solenoid plunger is measured using an ideal translational motion sensor connected to the circuit. The initial position of this is set to 5mm inthe translational motion sensor. The scope is connected to the visualize its behaviour. The spring constant and damping parameters of the solenoid block was altered to obtain the desired graph.
Conclusion :
Giving input as the period for 2 seconds in the pulse generator to open and close the switch. When the switch is closed the solenoind block receives electrical power from the battery and plunger moves from port R to port C to hit the bell and produce sound.
Physical movements of the plunger is observed by using translational motion sensor and physical output is converted into simulink output model is displayed in the scpoe . By reducing the spring constant value and increasing the damping value will be reduced.
2. Thermistor :
Temperature source - 20 from 0 to 10 seconds, 27 from 10 to 30 seconds, 23 from 30 to 50 seconds.
Fan conditions - ON if the temperature above 25 degrees, OFF otherwise.
Simulink model explanation -
Signal building block is added to input the values as per given conditions.
At point 1, time = 0 sec to 10 sec. and temperature = 293k.
At point 2, time = 10 sec to 30 sec. and temperature = 300k.
At point 3, time = 30 sec to 50 sec. and temperature = 296k.
Controlled temperature source represents an ideal source of the termal energy, that can maintain controlled temperature difference regardless of the heat flow rate. The temperature difference is set by the physical signal port S. A poositive tempwerature difference causes the temperature at port B greater than the temperature at port A.
Thermistor is a type of resistor whose resistance is based upon the temperature.
A linear resistor is used to control the amount of the current from the battery.
The voltage sensor is used to convert the voltage measured between two points into physical signal and voltage source represents AC/DC.
Electrical reference block is given.
Solver configuration - each physical network represented by the connected simscape blocks requires solver setting information for simulation.
What is thermistor :
Thermistor is a device which measures temperature, its working is based on the relationship between resistance and temperature. Here in the simmulink the thermistor block which is positive temperature co-efficient thermistor. So here resistance od thermistor increases or decreases with respect to temperature. The output from the thermistor is actually in the form odf voltage or current. The increase in voltage/current indicates increases in temperature.
Controlled temperature source :
This block represents an ideal source of thermal energy that is poerful enough to maintain specified temperature difference across source regardless of the heat flow consumed by the ssytem.
Connect a point A and B are thermal observing ports correspoinding to source of inlet and outlet respectively Port S is the physical signal port through which the control signals that drive the source is applied.
Thermistor :
It is a type of resistor whose resistance depends upon temperature dependent on temperature, more than in standard resistors. This thermistor word is a combination of thermal and resistor
Resistor :
This is the linear resistor, described with the following equation
V = IR
Where V = voltage
I = Current
R = Resistance
Voltage sensor :
This device converts the voltage measured between two points of an electrical circuits into physical signals proportional to the voltage.
Voltage source :
It implements the voltage source with DC/AC and Noise components.
Electrical reference :
It represents an electrical ground. Electrical conserving ports of all the blocks that are directly connected the ground must be connected to the electrical components must contain atleast one electrical reference block.
In this model the signal block is used to get temperature signal for the controlled temperature source(heater).
The temperature of the heater is supplied to the thermistor to sense it. Now in order to run the fan when temperature reaches the value of 298k we have to trigger the circuit with some external supply of the battery and as there is no device to calculate the resistance value of thermistor so we have attached another resistor in series across the terminal in series. The voltage sensor is attached across the resistor to calculate the voltage drop into it and this voltage drop value is inputted as thershold value to switch to start the fan and fan will go on when thershold value is more than 0.109.
From 0-10 seconds fan is OFF because the temperature is 293k which is below 298k, after 10 seconds it goes to 300k, so fan will turn ON because temperature exceeds 298k. After 30 seconds fan will turn OFF because temperature goes 296k less than 298k.