Week -2

Q: Make a Simulink model of Doorbell using solenoid block.

A: The Simulnik model of Doorbell can be built by using following blocks:

1. Solenoid block 2. Ideal Translational motion sensor 3.Battery 4. SPST switch operated through voltage trigger

A pulse generator is used to give voltage pulses over a regular interval of 2 sec so that SPST switch is ON & OFF for 2 sec. Same can be observed via Scope. Please refer attached image "Switch ON-OFF status".

The solenoid is connected to the battery via SPST switch. The solenoid can be energized and de-energized by means of SPST switch.

Ideal translational motion sensor is connected to Solenoid block, to provide the linear motion of plunger when Solenoid is energized. The response of Ideal Translational motion sensor largely depends on paramters of Solenoid block, such as spring constant, damping etc.

For example, please refer Graph-1 atatched heerwith. It represents characteristics of translational sensor with values of spring constant - 200 N/m and damping-1.5 N/(m/s)

While Graph-2 represents characteristics of translational sensor with values of spring constant - 60 N/m and damping- 2 N/(m/s).

The oscillations can be controlled by changing above parameters.

Q: Use a thermistor to sense the temperature of a heater & turn on or turn off the fan as per the below conditions:

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

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

A: The Simulink model for Fan control can be built by using following blocks:

1. Signal Builder

2. Controlled Temperature Source

3. Thermistor

4. Battery

5. Voltage sensor & Resistor

6. Switch

Signal Builder block genrates the required temperature variations i.e.

From 0-10 sec: 20 deg. C (293 K), From 10-30 sec: 27 deg. C (300 K), From 30-50 sec : 23 deg. C (296 K)

This data is fed to the physical signal port S of Controlled Temperature Soruce. A positive temp. difference casues the temp. at port B higher than temp. at port A.

Thermistor block parameters: Nominal Rsistance R0 at Ref. temp. T0 = 1000 ohm

Characteristic Temp. constant B = 3500 K

Referenec Temp. T0 = 298.15 K

A battery with 24V, Resistor of 1000 ohm and a voltage sensor are introduced in the circuit, to convert thermistor status into physical signal. The resistance of thermistor decreased with increase in temperature. So, the current through external resistance increases. The voltage sensor measures the volatge drop across external resistance and converts it into a physical signal proportional to this voltage.

The switch changes its state between ON & OFF depending upon voltage sensor output.

The model for Fan ON/OFF, plots for temperature variation, Switch ON/OFF staus and voltage sensor output are attached herewith.