Week -2

Aim 1: To make Simulink model of Doorbell using Simulink block.

Solenoid:

A 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. The coil can be arranged to produce a uniform magnetic field in a volume of space when an electric current is passed through it. The term solenoid was coined in 1823 by Andre-Marie Ampere to designate a helical coil.

In the study of electromagnetism, a solenoid is a coil whose length is substantially greater than its diameter. The helical coil of a solenoid does not necessarily need to revolve around a straight-line axis; for example, William Sturgeon's electromagnet of 1824 consisted of a solenoid bent into a horseshoe shape.

In engineering, the term may also refer to a variety of transducer devices that convert energy into linear motion. In simple terms, a solenoid converts electrical energy into mechanical work. The term is also often used to refer to a solenoid valve, an integrated device containing an electromechanical solenoid which actuates either a pneumatic or hydraulic valve, or a solenoid switch, which is a specific type of relay that internally uses an electromechanical solenoid to operate an electrical switch; for example, an automobile starter solenoid or linear solenoid. Solenoid bolts, a type of electromechanical locking mechanism, also exist. In electromagnetic technology, a solenoid is an actuator assembly with a sliding ferromagnetic plunger inside the coil. Without power, the plunger extends for part of its length outside the coil; applying power pulls the plunger into the coil. Electromagnets with fixed cores are not considered solenoids.

Condition:

Create a situation where a switch is closed for 2 seconds and then released. Observe the physical movement of the plunger.

Simulink Model:

As shown in the figure the following blocks are used for the doorbell simulation. Here the electrical supply is converted to the mechanical power. The signal sent through ‘pulse generator’ is Simulink signal which can’t be read by ‘switch’. Therefore, there is a need of the ‘Simulink-PS Convertor’ to convert Simulink signal to physical signal. The provided physical signal should be greater than the threshold of the switch, for switch being closed, or else it will open. The whole electrical system is connected to the ‘electrical reference’ so that proper earthing is provided to the system. In the ‘Solenoid block’, R and C are the ports that represents plunger and fixed port respectively. Now this R is connected to the R of the ‘Ideal Translational Motion Sensor’ block which senses the position of the plunger in the solenoid block and gives the output. In the ‘Ideal Translational Motion Sensor Block’ the outputs are V and P which represents velocity and position of the plunger. We need to observe only the motion of the plunger therefore, we will connect only P port with the scope via ‘PS-Simulink convertor’. If we need to find the velocity output then we need to add another ‘PS-Simulink convertor’ and the ‘scope’. Now C is the mechanical translation conserving port, which means that the mechanical process starts from R and ends at C and the cycle goes on. Therefore, C in the ‘Ideal Translational Motion Sensor block’ is connected to the ‘Mechanical Translational Reference’ which represents a fixed point where it is rigidly clamped in real time. Similarly, C of the ‘Solenoid block’ is also connected to the same ‘Mechanical Translational Reference’ as fixed point for the solenoid.

Pulse generator block parameters:

 Pulse Generator Block Scope Result:

In this graph the X axis represents time and Y axis represents amplitude. We can see that as we have given the delay of 2 sec therefore the pulse has started from 2 sec and was maintained at amplitude 1 for the time of 2 sec i.e., up to 4 sec and hence the cycle continues in this manner.

Scope 2 for Plunger position:

Here X axis represents time and Y axis represents plunger position.

Aim 2: To make a Simulink model using a thermistor to sense the temperature of a heater and turn on or off the fan.          

Thermistor:

A thermistor is a type of resistor whose resistance is strongly dependent on temperature, more so than in standard resistors. The word is a combination of thermal and resistor. Thermistors are widely used as inrush current limiter, temperature sensor (negative temperature coefficient or NTC type typically), self-resetting overcurrent protectors, and self-regulating heating elements (positive temperature coefficient or PTC type typically). An operational temperature range of a thermistor is dependent on the probe type and is typically in between −100 °C (173 K) and 300 °C (573 K).

Depending on materials used, thermistors are classified into two types:

• With NTCthermistors, resistance decreases as temperature rises; usually due to an increase in conduction electrons bumped up by thermal agitation from valency band. An NTC is commonly used as a temperature sensor, or in series with a circuit as an inrush current limiter.
• With PTCthermistors, resistance increases as temperature rises; usually due to increased thermal lattice agitations particularly those of impurities and imperfections. PTC thermistors are commonly installed in series with a circuit, and used to protect against overcurrent conditions, as resettable fuses.

Thermistors are generally produced using powdered metal oxides. With vastly improved formulas and techniques over the past 20 years, NTC thermistors can now achieve accuracies over wide temperature ranges such as ±0.1 °C or ±0.2 °C from 0 °C to 70 °C with excellent long-term stability. NTC thermistor elements come in many styles such as axial-leaded glass-encapsulated (DO-35, DO-34 and DO-41 diodes), glass-coated chips, epoxy-coated with bare or insulated lead wire and surface-mount, as well as rods and discs. The typical operating temperature range of a thermistor is −55 °C to +150 °C, though some glass-body thermistors have a maximal operating temperature of +300 °C.

Thermistors differ from resistance temperature detectors (RTDs) in that the material used in a thermistor is generally a ceramic or polymer, while RTDs use pure metals. The temperature response is also different; RTDs are useful over larger temperature ranges, while thermistors typically achieve a greater precision within a limited temperature range, typically −90 °C to 130 °C.

Condition:

Temperature source should be 20°C for 0 to 10 sec, 27 °C for 10 to 30 sec, 23°C for 30 to 50 sec. Fan condition should be ON if the temperature is above 25°C, OFF otherwise.

Simulation Model:

For this model we need to use many different blocks like thermistor, signal builder, controlled temperature source, resistor, voltage sensor.

The positive port of thermistor is connected to the positive port of the battery and the negative port of the thermistor is connected to the positive port of the resistor. The negative port of the resistor is connected to the negative port of the battery. Electrical reference block is also connected to the negative port of the battery for the proper earthing of the circuit.  To measure the voltage across the component the ‘Voltage Sensor’ block is connected in parallel to the resistor. In this case we need the fan to get ON and OFF at different temperatures. So, to provide temperatures, we have used ‘Controlled Temperature Source block’ which only gives a specified temperature as output even though heat flow is more. To send those corresponding signals we have used ‘Signal Builder block’ to set the signal according to our requirement. When we double click on the ‘Signal Builder block’ we can see the graph of temperature and time plot which we can modify according to our specification as shown in below figure:

Now when we double click on the scope connected to the ‘Volt Sensor’ via ‘PS-Simulink convertor’ we can get the graph as shown below:

This graph is plotted according to the conditions we have input in the ‘Signal Builder block’. We can see that X axis represent time and Y axis represents voltage. During 0 to 10 seconds at 293K the voltage is between 0.0095 to 0.01 V and from the time between 10 to 30 sec at 300K the voltage is between 0.0125 to 0.013 V and for time between 30 to 50 sec at 296K voltage is nearly 0.011. As given in the condition the fan should start above 25°C, therefore according to the above graph the fan should start above 0.011 V and should shut off below 0.011 V, so we will set the value of voltage in the ‘switch block’ that is of 0.011 V. We have connected two constant blocks with number 1 and 0 to the switch block. When the value of the ‘voltage sensor block’ will be more than the threshold value of the ‘switch block’ then it will pass the value 1 and if the threshold value is more than the ‘voltage sensor block’ value then it will pass the value 0.

 We have connected another scope to the switch block which concludes that the fan is On only at 300K and at remaining point it is OFF.