Week -2

1. Simulink model of Doorbell using Solenoid:

Objective:

To create a circuit model of an electric doorbell using solenoid with simulink.

Materials or Blocks used:

1. Pulse Generator:Block parameters: Pulse Generator attached below. The block generates pulse of amplitude 1 for a duration of 2 seconds. This signal is then converted to Physical signal using Simulink to PS Converter Block.
2. Switch:The Physical Signal is then connected or given to the switch as shown in the circuit as this converted physical signal controls the switch. The switch will be closed if the physical signal is above or greater than the threshold value. The block parameters of sitch is given below.
3. Battery: Here, we have used the battery of 24V with 4 ohms internal resistance. The block parameters are attached below.
4. Solenoid: This is the important part of the electric doorbell system. The block parameters are attached below. Here, F1 and F2 are forces corresponding strokes X1 and X2. The rated voltage is the voltage required to power the solenoid.
5. Ideal Translational Motion Sensor: This block measures the displacement mechanical translational system, here used for measuring the velocity or displacement of the plunger. The sensor is ideal since it does not account for the effect of inertia, friction, delays etc.
6. Solver Configuration
7. Mechanical Translational Reference
8. Electrical Reference
9. Simulink-PS converter and PS-Simuink Converter
10. Scope
11. Display

Theory:

Door Bell:

When we press a doorbell switch, we complete an electrical circuit that allows household electricity to flow through the doorbell's internal electromagnet. The magnetic field generated by the electromagnet is then used to power the mechanism that creates the doorbell sound. Doorbells are low voltage devices.

Solenoid:

A solenoid is a three dimensional structure of wire. When this wire is wrapped around a metallic block in a coil and electricity is passed through it, it has some special magnetic properties. Electromagnetic Induction makes it an electromagnet that can be switched on or off. The side in which the current appears to be passing in clockwise direction is south pole and in the anticlockwise direction is the north pole respectively. In other words, solenoid is a type of electromagnet, the purpose of which is to generate a controlled magnetic field through a coil wound into a tightly packed helix. Solenoid converts electrical enegy into mechanical work.

Working:

As said above, when we press the switch of the doorbell, the electric circuit will be closed and hence, the soleniod present inside the doorbell system gets enegised via the battery source as per the simulation model. Here, we are using the pulse generator inorder to control the switching operation. Here, the switch will be closed for 2 sec, after 2 sec, the switch will be opened. So, when the switch is closed, the battery charges the solenoid and hence the solenid act as an electromagnet. As we said earlier, solenoid is a deice that converts electrical energy into mechanical work, when the current passes through the solenoid, it gets magnetised and due to the magnetic force, it will attract the plunger which is a metallic strip so as to hit the bell causing to produce the bell sound.

Now, coming to the simulation model, the parts or the blocks and the connections highlighted in blue colour the electrical part. The green colour in the solenoid and the sensor represents the mechanical parts of the system. Here, it is also to be noted that the solenoid consists of both blue and green colour respectively as it is an electromechanical device. the blue colour part represents the coil and the green colour, the metallic strip which is the plunger. The movement of the plunger causes the doorbell to ring. The plunger motion is measured by a translational motion sensor which is plotted by the scope block. The simulation model of electric doorbell is attached below.

Result:

Position Signal:

For the first 2 seconds the electric circuit is closed and the doorbell rings. At t=2 sec, the circuit is open and hence the spring pulls back to it's original position. There will be slight oscillation in the plunger due to the spring stiffness for about a half second which is the damping effect. The plot is attached below.

Velocity Signal:

Below attachment is provided for the plot of the velocity signal of the plunger.

2. Temperature sensor monitor:

Objective:

To use a thermistor to sense the temperature of a heater and turn on or off the fan as per below conditions:

Temperature source: 20 deg C from 0 to 10 seconds, 27 deg C from 10 to 30 seconds, 23 deg C from 30 to 50 seconds.

Fan Conditions: ON if the temperature is above 25 deg C, OFF otherwise.

Model:

The simulation model for the above temperature sensor is attached below.

Blocks Used:

Signal Builder:

The Signal Builder Block allows us to create interchangeable groups of piecewise linear signal sources and use the in a model. We can quickly switch the signal groups into and out of a model to facilitate testing. In the Signal Builder window, create signals and define the output waveforms. The signal used for this model is shown in the attachment below.

Controlled Temperature Source:

The Controlled Temperature Source block represents an ideal energy source in a thermal network that can maintain a controlled temperature difference regardless of the heat flow rate. The temperature difference is set by the physical signal por S. A positive temperature difference causes the temperature at port B to be greater than the temperature at port A.

Simulink-PS Converter:

This Block converts the Simulink input signal to a Physical Signal.

PS-Simulink Converter:

This Block converts the input physical signal to a Simulink output signal.

Thermistor:

The term Thermistor comes from Thermal and Resistor. A thermistor is a type of resistor whose resistance is reliant on temperature; it is a resistance thermometer. They are made from metallic oxide which is molded into a bead, disk or cylindrical shape and then enclosed with epoxy or glass. There are two types of thermistors- the most commonly used is the Negative Temperature Coefficient thermistor (NTC). The NTC's resistance decreases as the temperature increases and vice versa. With the Positive Temperature Coefficient (PTC) thermistor, the resistance increases as the temperature increases and vice versa; it is normally used as fuse. The material used in the thermistor will dictate how much the resistance changes which is changed with temperature. Thermistors are nonlinear. Here, in the circuit, the temperature controller monitors the temperature of the thermistor which then instructs a heater or cooler (here, the fan or the universal motor which is used in the circuit) when to turn on or off, inorder to maintain the temperature of the sensor (Thermistor) as well as the target device. The block parameters of the Thermistor is given in the attachment below.

Positive Supply Rail:

The Positive Supply Rail Block represents ideal positive source supply. It can be used in place of the Foundation Library DC Voltage Source. The output voltage is defined relative to the Electrical Reference block. Use the Constant voltage parameter to specify the output voltage value. The block parameter is given below in the attachment.

Current Sensor:

The block represents an ideal current sensor, that is, a device that converts current measured in any electrical branch into a physical signal proportional to the current.

Battery:

We have used 12V battery with 2oh internal resistance. Block parameters are below.

Electrical Reference

Mechanical Rotational Reference

Thermal Reference

Thermal Reference

Solver Configuration

Scope

Universal Motor:

This block represents the electrical and torque characteristics of a universal motor (also sometimes called a series-wound motor). Block parameters are given below.

Ideal Rotational Motion Sensor:

This block measures angular velocity or angle in a mechanical rotational network. The sensor is ideal since it does not account for inertia, friction, delay stc. the block parameters are given below.

PS Switch:

Block parameter is given below.

Explanation:

Here in the circuit, we have used the signal builder block for providing the condition for the universal motor to be on or off. we generate a signal based on this cindition and it is fed to the controlled temperature source. The temperature source provides the input for the thermistor. The thermistor outputs a certain value of current which is detected by the current sensor and then converted into physical signals and given to the ps switch which controls the universal motor operation. Since as per the condition, the fan should be switched on above 25 deg C. For that, an input signal of 25 deg C is given to the temperature source which is given to the thermistor. The output current generated from the thermistor is set as the threshold value of the switch. So, whenever the temperature is above threshold value, the fan is switched on or switched off otherwise. Here, in this model we use universal motor instead of fan.

Results:

According to the inputs given to the model, using signal builder, the ouptu current is read by the current sensor and the angular velocity is read by the ideal rotational motion sensor. The output waveforms are given below.

Conclusion:

By the graphs provided, we can observe that the universal motor is active between the 10 sec and 30 sec, this is because this is where the temperature is above 25 deg C.