Induction furnace control system

3.6.4 LM 335Z  (Precision temperature sensor) :

This circuit is a very accurate temperature sensor that will switch off a motor when a predetermined temperature level is reached.

Circuit diagram:

Internal structure of LM335Z
Circuit diagram for LM335Z

Components

  1. SW1 = Toggle switch
  2. R1 = 10k ohm
  3. R2 = 10k ohm
  4. R3 = 1200 ohm
  5. R4 = 1k ohm
  6. R5 = 1200 ohm
  7. VR1 = 10k ohm
  8. VR2 = 10k ohm
  9. Power FET Transistor (BUK100)
  10. 7805 the voltage regulator
  11. Temperature sensor (LM335Z)
  12. 741 operational amplifier
  13. Motor/Solenoid (12V)

Operation:

The operational amplifier is used in the comparator mode. When the voltage at pin 3 is less than the voltage at pin 2, then the output at pin 6 is low (1.8V) approximately. When the voltage at pin 3 is greater than the voltage at pin 2, then the output the voltage at pin 6 is high (7V). R1 and R2 and the variable resistor VR1 placed in series form a voltage divider network and as such, the voltage on the wiper connection can be set to any required value.  This wiper connection is attached to pin 2 of the op amp. For ease of explanation a hypothetical voltage of 3.03V is set on pin 2.

The LM335.is a temperature sensor which produces an output of 10 mV / degree Kelvin.

To convert degrees Centigrade to degrees Kelvin, simply add 273 to the Centigrade scale, i.e. 30 degrees Centigrade = 273+30 = 303 degrees Kelvin.

The LM335 converts temperature levels to the voltage levels.

Thus the voltage drop across the sensor = 303 x 0.010 =3.03V.

The sub circuit R4, VR2, LM335 is arranged as shown.  Note the junction of R4 and VR2 is connected to pin three of the op amp.  VR2 is placed in the circuit to calibrate the sensor.

To carry out this task, a thermometer and voltmeter are required.

The temperature in which the sensor is placed must be recorded, add 273 to convert this temperature into degrees Kelvin, and then multiply the result by 0.010.  The voltage at pin 3 must be set to this value; i.e. the circuit is calibrated.

Consider now the ambient temperature is 25 degrees Centigrade.  Voltage output at pin3 = (273+25) x 0.010 = 2.98V.  Thus, the voltage at pin 3 is less than the voltage at pin 2, so output at pin 6 is low.

Consider now a temperature of 32 °C, Voltage at pin 3 is now 3.05 V.  Voltage at pin 3 is now greater than the voltage at pin 2, so output (pin 6) now is high.

The LM 335 sensor is so precise that even a very small voltage fluctuation can upset it. For this reason the rail voltage must be constant, as the output from a small battery is liable to change a voltage regulator is inserted.  To clamp the voltage rigidly to 5 V i.e. a voltage regulator-7805 is used.

Output: In this case, a special transistor is used as a switching device (BUK 100).

With less than 2V on the GATE, the transistor is switched off.  No current can flow through the motor. With more than 2V, the transistor switches on, current can now flow in the 12V circuit.  Note the output of 741 Op-amp is connected to a voltage divider circuit R3, R4.  Connection to the gate of the transistor is from the junction of R3, R4.

CIRCUIT DIAGRAM :

Circuit diagram of Induction furnace control system
Circuit diagram of Induction furnace control system

Working:

Our circuit is mainly based on the working of transistor. We know that, a transistor can work in two different ways; as an amplifier and as a switch.

Here we are using transistor as a switch. Working of transistor as a switch can be understood with the help of circuit diagram given in the figure. Positive terminal of 5V battery is connected to the collector of transistor while negative terminal is connected to emitter after a lamp.

Transistor as a switch
Transistor as a switch

When switch ‘S’ is open, there is no current through base terminal and hence collector-emitter is also isolated. Thus, the lamp will not glow. Now if we close switch S, 0.2V battery will be connected to base, which will give very small current to the base terminal. This small  current will short collector to emitter and the lamp will glow. Here lamp will glow due to 5V battery but not due to 0.2V battery.

In short, if we provide very small current to the base terminal, collector and emitter will be shorted.

In this circuit, we are controlling opto-isolator’s L.E.D. through software using printer port also called parallel port. In an opto-isolator, if L.E.D. integrated inside I.C. is lighted, it generates small current for base terminal of the integrated transistor.

Thus, the transistor is switched on. We also use one external transistor for delivering proper & operating current to the Relay.

Now, when L.E.D. is lighted by software, it switches on the internal and thus the external transistor, which further switches the relay or supply potential difference to the relay coils. Now if there is a potential difference across the relay coils, the iron core of relay coil converts into Electro-magnet.

This Electro-magnet attracts the iron connected to the moving hand of relay thus switches on the mains supply.

3.9 FLOW CHART :

Flowchart of the program
Flowchart of the program
Editorial Team
Editorial Team

We are a group of young techies trying to provide the best study material for all Electronic and Computer science students. We are publishing Microcontroller projects, Basic Electronics, Digital Electronics, Computer projects and also c/c++, java programs.

3 thoughts on “Induction furnace control system

  1. Some very fascinating factors however i think your analysis and bias leaves rather a lot to be desired. Then of course, that’s just my opinion. Have an amazing day undoubtedly a thought-frightening post.

Leave a Reply

Your email address will not be published. Required fields are marked *

Get the latest updates on your inbox

Be the first to receive the latest updates from Codesdoc by signing up to our email subscription.

    StudentProjects.in