Temperature control
Here is the circuit of a simple and inexpensive temperature controller which can control temperature from about 20°C to 200°C with an accuracy of 0.5°C
PARTS LIST
| R1 , R2 , | 8.2 K |
| R4 | 1K THERMISTOR |
| R5 | 470 Ohm |
| R6 | 22 K |
| R7 | 820 Ohm |
| R3 | All 100 Ohm |
| D1 | Zener diode 5.1V 400mW |
| D2 , D5 , D6 | 1N4001 |
| D3 , D4 | 15V 1W |
| IC1 | op-amp 741 |
| T1 | BC147 |
| X1 | 18V |
| C1 , C2 | Capacitor 470μ 50 V |
| R1 | RELAY 12V 250Ω |
| S1 | 1-POLE, 10 way switch |
CIRCUIT DIAGRAM
CIRCUIT DESCRIPTION
The controller has been designed and fabricated using the op-amp IC 741 and a 1k thermistor as the temperature sensor. It is based on the principle of Wheatstone bridge. The ratio arms R1 and R2 of the bridge are kept fixed (say unity). The voltage across the thermistor, i.e. across the arm R4, is compared with the voltage across the variable arm R3 which is kept fixed for a particular temperature (using the op-amp).
When the bridge is not balanced the output of 741 drives transistor BC147 to conducting state. Thus, the relay is energised and switches the heater on. As the temperature increases, the voltage across the thermistor decreases and when this voltage is equal to the voltage across R3 (i.e. the preset value) the output of 741 becomes zero. The transistor then stops conducting, the relay is de-energised, and the heater is switched off. Band switch S1 gives the different ranges of temperature and potentiometer VR1 is used for fine adjustments
I AM WANT TO JOIN THE PROJECT TEAM.
I WANT TO MAKING A BEST PROJECT.
i made one using a sensor
I am using a temp.controller made by eltech.It contains electronic circuit with ic and 6v relay ,a tranformer230 to6v.This controller i am using on plastic moulding machine where polyacetal copolymer requires precision temp.Company stopped making this product and i am unable to repair it as its ic no. is scrathed.I need such controller.
could a K or J type thermocouple be use instead of the thermistor
Thank you very much for sharing this circuit. I attempt to adapt it to variety of homemade plastic-melting devices, operating between 200 and 300 celcius degrees. Would you be so kind as to inform me which components should be replaced, in order to make this circuit operate on such a temperature range?
I have an extremely limited education in electronics, so any clarification would be greatly appreciated.
Yours,
Emilio Leotta.
Buenos Aires, Argentina.
How to increase the temperature range? Can u suggest some idea?
if any one can design the values of following resisters r6, r5, r8, vr1
can any one help me for designing using LM35
Can I use the circuit to control temperature up to 250 C centigrade.
And what modifications should be done to do so.
Thank you and best regards.
I have several outdoor installations where I will need to turn on a low wattage heater when the temperature drops below a -20 F°. I was wondering since I have a 24vdc power supply, can I eliminate D5, D6, X1 and substitute the bridge with a resistor between S1 and R1 as shown by the dotted line R3.
so what is R8 and vr1?
according to temp control circuit ,what is value of R8 and vr1.
What is the Value of Resistance R8, in the given circuit
I built this circuit, but i am not getting any voltage at the output.