Week -2

1. SIMULINK MODEL FOR DOORBELL USING SOLENOID BLOCK :

Solinoid is a type of electromagnet, The electromagnetic coil is connected to the battery. The coil can move forwards and backwars through the electromagnetic field. When the switch is turned on, the current flows through the electromagnetic coil which draws the iron core to the magnetic field. When the end of the piston strikes the bell, producing the ringing sound.

The below simulink model(fig 1.1) shows the arrangement of a doorbell using solenoid block. As the input signal, pulse generator is used to generate a pulse in every 2 seconds. The parameters of the pulse generator mainly the time period is set to 4 seconds with a pulse width of 50%, then the pulse is produced in every 2 sec. This input signal reaches the PS port of the switch, placed between the solenoid and battery blocks through the simulink-PS converter, which convert the input signal from the pulse generator to physical signals. This switch is controlled by an external physical signal and for it to work, the provided physical signal should be greater than the threshold value(0.5) of the switch. An electrical reference is connected in between the -ve terminal of the battery and solenoid. The electrical reference is used for the electrical grounding or earthing. In the solenoid block, ports 'R' and 'C' represents plunger and fixed point respectively. The port 'R' of the solenoid is connected to the 'R' port of an ideal translational motion sensor, which senses the position of the plunger and gives the output. The 'C' port of the ideal translational motion sensor is connected to the 'C' port of the solenoid. A mechanical translational reference is connected in between the respective 'C' ports of the ideal translational motion sensor and solenoid. The output ports of ideal translational motion sensor 'V' and 'P', representing velocity and position of the plunger respectively. As we are taking the position of the plunger into consideration, the output signal from the 'P' port is converted back to a simulink value by a PS-simulink converter and sent to the scope to generate a graph to detect the change in position of the plunger. A solver configuration block is also connected.

fig 1.1

RESULT : The below graph(fig 1.2) represents the input signal from the pulse generator, where pulse of amplitude 1 is generated for every 2 seconds for a time period of 10 seconds. The output scope is graph(fig1.3), which shows the physical movement of the plunger. Here the X-axis denotes the time and Y-axis denotes the position of the plunger. we can detect a noise/disturbance at the initial time(t=0sec), which continues on at every 2 second time interval,on the basis of the input pulse from the pulse generator. At the first interval, the graph shows disturbances to a negative value,which gets damped over time and at the next 2 sec interval, it again disturbances to a positive value,getting damped over time and continues this cycle till the time period get 10 seconds.

fig 1.2

fig 1.3

2. THERMISTOR :

DESCRIPTION : Thermistor is a semiconductor device having a resistance capacity more than conducting materials and less than insulating materials. Its resistance varies with the change in the temperature, ie it is thermally sensitive resistor. There are mainly two type of thermistors, Negative temperature coefficient(NTC) and Positive temperature coefficient(PTC) thermistors. A negative temperature coefficient thermistors resistance decreases with the increase in temperature, while a positive temperature coefficient thermistors resistance increases with the increase in temperature. In this challenge, a NTC is used.

The below simulink model(fig 2.2) shows the thermistor arrangement. The input signal is built by a signal builder block depending upon the the conditions given in the question. The input signal is built by a signal builder by changing the following parameters, firstly the time range is changed to the interval 0-50 seconds. Then the signal is changed by customizing new time(X) values: [0 10 10 30 30 50] and Y values(in kelvin): [293.15 293.15 300.15 300.15 296.15 296.15]. Then that built signal is converted to physical signal by simulink-PS converter and is sent to the 'S' port of a controlled temperature source. A positive temperature difference causes temperature at port 'B' to be greater than temperature at port 'A'. The controlled temperature source provides the required temperature. The port 'A' of the controlled temperature source is grounded by a thermal reference and port 'B' is connected to the port 'A' of the thermistor. The thermisor block has a +ve and -ve terminals. The battery source is connected in parallel with the thermistor and the in series with resistor. Between the battery and resistor an electrical reference is connected for the earthing of the circuit. A solver configuration block is connected to thermistor circuit. A voltage sensor block is provided across the resistor block to measure the voltage change during the temperature inputs. The output signal of the voltage sensor is converted to a simulink value by PS-simulink converter and sent to the port 2 of the switch. The accurate result get in the scope when the simulink-PS converter provides the filter input.

The switch has 3 input ports

1. port 1 is turned on when the signal value is greater than the threshold value.
2. port 2 is used to find the condition of the signal input in the switch (whether the following simulink value is greater than or less than the threshold value of the switch).
3. port 3 is turned on when the signal value is less than the threshold value.

The simulink value from PS-simulink converter is given to the port 2 of the switch, which check the condition whether the following simulink value is greater than or less than the threshold value of the switch and turn on the port satisfying the above condition. The port 1 is connected to a constant block of value 1 and port 3 is connected to a constant block of value 0. When the simulink value at port 2 is greater than the threshold value of the switch, then port 1 is turned on with value 1 and if the simulink value is less than the threshold value, then port 3 is turned on with value 0. To find threshold value of the switch, the input signal builder block is removing and commenting out, and replacing it by a constant block of input value 298.15 Kelvin(25 °C) as given in the question , and also a display block is connected in between the switch and voltage sensor(fig 2.1). Now running the simulation, the display shows the value 0.01196 ; this value is taken as the threshold value of the switch and is input to the switch. The output of the switch is connected to the scope.

fig 2.1

fig 2.2

RESULT : The below graph(fig 2.3) shows the operation of the thermistor that measures the temperature to turn ON or turn OFF the fan on the basis of conditions mentioned in the question.

• During the time interval (t= 0-10 sec), at 20 °C(293.15 K), the port 3 of the switch (0) is turned on as the simulink value from the converter is less than the threshold value(0.01196) of the switch. The fan is turned OFF during this interval as the temperature is less than 25 °C(298.15 K).
• During the time interval (t= 10-30 sec), at 27 °C(300.15 K), the port 1 of the switch (1) is turned on as the simulink value from the converter is greater than the threshold value, So the fan is turned ON during this interval as the temperature is greater than 25 °C(298.15 K).
• During the time interval (t= 30-50 sec), at 23 °C(296.15 K), the port 3 of the switch (0) is turned on as the simulink value from the converter is less than the threshold value, So the fan is turned OFF again during this time interval as the temperature is less than 25 °C(298.15 K).

fig 2.3