Week -2

Q.1

AIM- To construct a simulink model of a doorbell using solinoid.

Theory-

For this we are making use of a solinoid block. A solinoid takes electrical input and stores the energy in magnetic field.The plunger displaces as it faces magnetic force of attraction.

The electrical end of solinoid is connected to dc voltage source through a switch.The physical signal governing the switch action is given a signal where the switch acts for 2 seconds and then it switches off. The solinoid's plunger ends r and c is connected to ideal transitional motion sensor, whose position is connected to a scope (output). To remove the transients we have used a translational damper acoss the r and c terminal of the plunger. Here we used two references, electrical and mechanical translational reference. To solve the equation we have used a solver.

Q2.

AIM- To use a thermistor to sense temperature of a heater, and switch on the fan if the temperature exceeds 25 degree CELCIUS.

THEORY-

For this we have divided the model into three parts.

1. Temperature source -

The temperature source used here is a controlled temperature source.The temperature used here is in kelvin as the default reference temperature parameters are in kelvin. The physical signal governing the temperature source is such that in a simulation time of 50 seconds, temperature is 20,27,23 degree celcius for 0 to 10,10 to 30 and 30 to 50 seconds respectively. The temperature source is connected to thermistor.

2. Electrical circuit connected to thermistor -

A thermistor is an instrument that senses temperature and generates a curent signal depending on the temperature. We have connected it to a dc voltage source and a resistor in series. Across the resistor, voltage sensor is used to detect voltage across the resistor for different temperature inputs.For temperature of 25 deg. celcius, we get a voltage of 0.01189 which is used as theshold value in the switch, connected to voltage sensor. The switch provides an if-else condition, where the logic stands : if voltage across resistor is greater than threshold voltage then a value of 10 volts will go to controlled voltage source of dc motor,otherwise 0 volts will go. Hence ensuring temperatute over 25 deg. celcius will lead to starting the motor,to which fan is connected.

3. Fan connected to motor -

A controlled dc voltage source is connected to a dc motor, which is running a fan load. the fan load has torque speed equation as T=8*e^(-8)w^2. Here T is torque and w is angular speed.

To have a clear understanding, the model is divided in subsystems, performing a particular task.

The current of the motor tells us about the state of fan, i.e. when the current is 0, then the fan is not running ,otherwise it is running. Hence finally as output, the motor current is scoped and temperatue is scoped as input.