Week -2

1 Doorbell problem

Introduction

solenoid- A solenoid is a coil of wire in a corkscrew shape wrapped around a piston often made of iron.As in all electromagnets, a magnetic field is created when an elctric current passes through the wire.Electromagnets have an advantage over permanent magnets in that they can be switched on and off by the application or removal of the electric current, which is what makes them useful as switches and valvesand allows them to be entirely automated.Like all magnets the magnetic field of an activated solenoid has positive and negative poles that will attract or repel material sensitive to magnets .In a solenoid, the elctromagnetic field causes the piston to either move backward or forward, which is how motion is created by a solenoid coil.

procedure

open matlab and go to simulink blank page

according to problem we need to build a signal which is switd=ched on for 2 seconds and then released.Therefore first block which we need to focus on is pulse generator.

screenshot(14) shows pulse generator Amplitude is kept 1 .Period is kept 4 sec and accordingly % width for a 2 sec signal comes out to be 50.

Now we need to convert this simulink block into physical signal for the switch process.Therefore we used Simulink to ps converter.Threshold value of switch is kept at 0.5 in order to switch on the switch when the amplitude of input signal is greater than Thresold.Now for the solenoid to operate we need an electric supply, which is given bu=y a 12v battery.Complete the circuit accordingly.Once the electrical energy is converted to mechanical energy using a solenoid we need to sence the translational motion sensor using an ideal translational motion sensor.Also because energy conversion is taking place, we need a solver configuration to solve the partial differential equations accordingly.

we need to ground the circuits as well, therefore mechanical and electrical references are also used accordingly.At last we need to convert the physical signal of translational motion sensor into simulink signal using ps simulink converter and the results are observed in display and scope.

from screenshot(16) it is clear that displacement of piston is 0 when the switch is turned off.But when the switch is turned on (for example in 0-2sec). there is a displacement in piston is observed.Fluctuations are observed because of the damping and stiffness of solenoid.

Thermister Problem

Thermister

A thermistor is a resistance thermometer, or a resistor whose resistance is dependent on temperature. The term is a combination of “thermal” and “resistor”. It is made of metallic oxides, pressed into a bead, disk, or cylindrical shape and then encapsulated with an impermeable material such as epoxy or glass.

There are two types of thermistors: Negative Temperature Coefficient (NTC) and Positive Temperature Coefficient (PTC). With an NTC thermistor, when the temperature increases, resistance decreases. Conversely, when temperature decreases, resistance increases. This type of thermistor is used the most.

A PTC thermistor works a little differently. When temperature increases, the resistance increases, and when temperature decreases, resistance decreases. This type of thermistor is generally used as a fuse.

Typically, a thermistor achieves high precision within a limited temperature range of about 50ºC around the target temperature. This range is dependent on the base resistance.

Procedure

Open matlab and go to simulink and open a blank sheet

According to the problem we need to build a temperature source which a thermister senses and later gives the signal to the switch to turn on and off the fan.This temperature source is varying with time therefore we use the block named controlled temperature source.This source needs signal which consistsdifferent temperature values for different time intervals.This signal is built using repeating sequence stair block .For a 50 sec flow time, 10 sec is kept sample time for this block and respective temperature values are added.

From figure it is clear that angular velocity is 0 in the time interval of 0-10 sec because temperature is 20 degree.In 10-30 sec interval temperature is 27 degree hence angular velocity is non zero.In 30-50 sec interval although temperature is 23 degree angular velocity is non zero because of the inertia induced in the DC motor.