Week -2
- Doorbell using solenoid block :
Description : An electromagnetic doorbell uses a sollenold, which Is an electromagnet with a wire coiled around it; surrounded by a piston which consists of an iron core mounted on a non-magnetic metal bar. It can move forwards/backwards through the electromagnetic field. When the switch Is turned on, the current flows through the electromagnet which draws the Iron core to the magnetic field;where the end of the piston strikes the bell,mainly placed in both sides of the piston, producing the ringing sound.
The slmullnk model(l.O) depicted below 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 sec with a pulse width(%) of 50%.As shown In the fig, a pulse Is produced 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 converts the input signal from the pulse generator to physical signals. This switch is controlled by an external physical signal(PS) and for it to work, the provided PS should be greater than the threshold value(0.5) of the switch. An electrical reference Is connected in between the negative terminals of the battery and the solenoid,representing electrical grounding/earthing. n the solenoid block, ports 'R' and 'C' represents plunger and fixed point respectively. The R port 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'(casing) port of the ideal translational motion sensor is connected to the fixed point ('C') of the solenoid. A mechanical translational reference is taken and connected In between the respective 'C' ports of the Ideal translational motion sensor and the solenoid. The outputs ports of Ideal translational motion sensor 'V' and 'P', representing velocity and position respectlvely of the plunger. As we are mainly taking the position of the plunger Into consideration, the output signal from the 'P' port ls converted back to a slmulink value by a PS-slmullnk converter and sent to the scope to generate a graph to detect the change in the position of the plunger.
Result : The below graph(flg 1.2) represents the Input signal from the pulse generator, where pulse of amplitude 1Is generated for every 2 seconds(Je, having a pulse width of 50%) for a total time period of 10 seconds. The scope at the output provides the graph(fig 1.1), 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 disturbance/noise at the initial time(t= O sec),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 oscillations from O to a negative value, which gets damped over time and at the next 2 second interval,it again oscillates from O to a positive value, getting damped over time and it continues to do so at the next 2 second interval. By increasing the damping,we can also smoothen the noise signal
fig 1.1
fig 1.2
- Thermistor :
Description: It is a semiconductor device,having a resistance capacity more than conductors and less than Insulators. ts resistance varies with the change in the temperature, ie Its a thermally senslt.ive resistor. There are mainly two types of thermistors, mainly negative temperature coefficient(NTC) and positive temperature coefficient(PTC) thermistors. A negative temperature coefficient thermistor's resistance decreases with the Increase In temperature, while a positive temperature coefficient thermistor's resistance Increases with the increase in temperature . n this challenge, a NTC Is used.
The slmullnk model(flg 2.1) depicts the thermistor arrangement. The Input signalIs built by a signal builder block depending upon the conditions given In the question. The Input signal Is built by a signal builder by changing the follow ing parameters; firstly the time range is changed to the Interval 0-50 seconds. Then, signal is changed by customizing new time(X) values: [O 10 10 30 30 5O] and Y values(in Kelvin): [293.15 293.15 300.15 300. 15 296.15 296. 15]. The newly built signal is converted to physical signal(PS) by simullnk-PS converter and Is sent to the PS port 'S' 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, according to the signal provided to its port A/source inlet of the controlled temperature source. The port A of the controlled temperature source is grounded by a thermal reference and port B is connected to the thermalport 'A' of the thermistor. The thermistor block has a positive and negative terminals,along with the thermal port{A).The battery sourceis connected In parallel with the thermistor and the resistor block in series with the thermistor block. An electrical reference is connected in between the battery source and the resistor,representing earthing/grounding of the 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 simullnk value by PS-slmullnk converter and sent to the port 2 of the switch. This particular switch has three input ports;
- Port 1is turned on when the signal value Is greater than the threshold val
- Port 2 Is used to find the condition of the signal Input In the swi le, whether the following slmullnk value Is greater than or less than the threshold value of the switch.
- Port 3 is turned on when the the signa l value is less than the threshold val
The simullnk value from the PS-simulink converter is given to the port 2 of the switch,which checks the condition whether the following simulink value is greater/less than the threshold value of the switch and turns on the port satisfying the above condition. The port 1is connected to a constant block of value 1and port 3 is connected to a constant block of va lue o. So, when the simulink value at port 2 is greater than the threshold value of the switch,port 1Is turned on with value 1and if the simulink value Is less than the threshold value, port 3 Is turned on with value 0. To find the threshold value of the switch,a display block is connected In between the switch and the voltage sensor and the input signalIs taken from a constant block, removing and commenting out the signal builder block. The constant which is taken as the input(fig 2.2) is given the value 298. 15K(25° C) as given in the question and running the program, the display shows the value 0.01196; taken as the threshold value of the switch and is inputed into the switch. The output of the switch is then connected to the scope.
fig 2.1
fig 2.2
Result :The graph(fig 2.3) below depicts the operation of the thermistor that measures the temperature to turn ON/OFF the fan on the basis of the above conditions. The followlng are the observations taken;
- 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 slmulink value from the converter Is less than the threshold value(0.01196) of the switch. The fan Is turned OFF curing this Interval as the tempemture ls less than 25 °C(298.15 K).
- During the time lnterval(t= 10 30 sec),at 27 °C(300.15 K), the port 1of the switch (1) Is turned on as the slmullnk value from the converter Is greater than the threshold value. So,the fanIs turned ON during thisInterval as the temperature is greater than 25 c.
- During the time lnterval(t= 30 50 sec),at 23 °C(296.15 K), the port 3 (0) Is turned on as the slmulink 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 greater than 25 •c.
fig 2.3