Week -2

1. DOORBELL USING SOLENOID BLOCK

DESCRIPTION: An electromagnetic doorbell uses a solenoid, which is an electromagnet with a wire coiled around it, surrounded by a piston which consists of a non-magnatic metal bar. It can move forward or backward 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 ring sound.

The simulink model (fig 1.1) depicted shows the arrangement of a doorbell using solenoid block. The signal builder is used to generate a pulse signal for 2 second as an input signal. The input signal reaches the PS part of the switch placed between the solenoid and battery through the simulink-PS convertor which converts the inut signal from the signal builder 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 solenoid, representing electrical grounding. In the solenoid block, port R and C represents the 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 port of the ideal translationnal motion sensor is connected to the fixed point C of the solenoid. A mechanical translational reference is taken and connected between the respective C ports of the ideal translatioal sensor and the solenoid. The output ports of the ideal translational motion sensor V and P represents velocity and position respectively. As we are taking position of the plunger into consideration, the output signals from the P port is to converted back to simulink value by passing through PS-Simulink converter and connected to the scope.

Fig 1.1 Simulink model of doorbell using solenioid

RESULT: The below image (fig 1.2) depicts the input signal from the signal builder block, where the pulse amplitude 1 generated for 2 seconds(from t=4 to t=6). The scope at the output provides the graph (fig 1.3), which shows the physical movement of the plunger. Here X-axis denotes the time and Y-axis denotes the postion of the plunger. We can detect a noise at t=4 sec and at t=6 sec. The noise level change according to the damping of solenoid, here the daming is given 4N*s/m. By increasing the damping we can smoothen the noise signal. The output graph shows oscillation from 0 to a negative value, getting damped over time and reaches zero.

Fig 1.2

Fig 1.3

2. THERMISTOR :

DESCRIPTION: Thermistor is a semiconductor device. Its resistance varies with the change in the temprature, ie its a thermally sensitive resistor. There are mainly two types of thermistors, mainly negative temprature coefficient(NTC) and positive temprature coefficient(PTC). In this challenge a NTC is used. The simulink model(fig 2.2) depicts the thermistor arrangement. The input signal is built by a signal builder by changing the following parameters. Firstly the time range is changed to 0-50 seconds. Then signal is changed by customizing new time(X) values:[0 0 10 30 30 50] and Y values:[293 293 300 300 296 296]. The newly built signal is converted to physical signal by simulink-PS convertor and is sent to the PS part S of a controlled temprature source. A positive temprature difference causes temprature at port B to be greater than temprature at port A. the controlled temprature source provides the required temprature, according to the signal provides to its port A inlet of the controlled temprature source. The port A controlled temprature source grounded by a thermal source and port B is connected to thr thermal port A of the thermistor. The thermistor block has a positive and negative terminals, along with the thermal port A .The battery source is connected in parallel with thermistor and the resistor block is in series with the thermistor. An electrical reference is connected in between thenthe battery source and the resistor. A voltage sensor block is provided across the resistor to measure the voltage change during the temprature inputs. The output signal of the voltage sensor is converted to a simulink value by PS-simulink convertor and sent to port 2 of the switch, which checks the condition wheter the following simulink value is greater or less than the threshold value of the switch and turns on the port satisfying the above condition. The port 1 is connected to a constant block of a value 1 and port 3 is connected to a constant block of value 0. So, when the simulink value at port 2 is greater than the threshold value of the switch, port 1 is turned on with value 1 and if the simulink value is less than threshold value, the port 3 is turned on with value 0. To find the threshold value, a display block is connected betweeen the switch and the voltage sensor and the input signal is taken from a constant block, removing and commenting out the signal builder block(as in fig 2.1). The constant value is 298K(25 C) as given in the question. By running the stimulations the display shows the values of 0.01189, which is taken as the threshold value of the switch and is inputed into the switch.

Temprature source: 20°C from 0 to 10sec, 27°C from 10 to 30 sec, and 23°C from 30 to 50sec.

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

Fig 2.1

Fig 2.2

Fig 2.3

RESULT: The fig 2.3 depicts the operation of the thermistor that measures the temprature to turn ON/OFF the fan on the basis of above conditions. The following are the result;

• During the time intervel;t=0 to t=10 sec, at 20°C(293K), the port 3 of the switch is turned ON, as the simulink value from convertor is less than the threshold value,0.01189.And the fan is turned OFF during this intervel as the temprature is less than 25°C.
• From t=10 to t=30 sec, at 27°C(300K), the port 1 of the switch is turned ON, as the simulink value from the convertor is greater than the threshold value.And the fan is turned ON as during this intervel as the temprature is greater than 25°C.
• From t=30 to t=50 sec, at 23°C(296K), the port 3 of the switch is turned ON, as the simulink value from the convertor is less than threshold value. And the fan is turnned OFF again during this untervel as tge temprature is less than 25°C.