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Automatic heat detector


walid
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Hi
I found this circuit Saved in my PC (pdf formatt) and I do not know of any site obtained.
autoheat.jpg

This circuit uses a complementary pair comprising npn metallic transistor T1 (BC109) and pnp germanium transistor T2 (AC188) to detect heat (due to outbreak of fire, etc) in the vicinity and energise a siren. The collector of transistor T1 is connected to the base of transistor T2, while the collector of transistor T2 is connected to relay RL1.

This part is what concerns me now
The second part of the circuit comprises popular IC UM3561 (a siren and machine-gun sound generator IC), which can produce the sound of a fire-brigade siren. Pin numbers 5 and 6 of the IC are connected to the +3V supply when the relay is in energised state, whereas pin 2 is grounded. A resistor (R2) connected across pins 7 and 8 is used to fix the frequency of the inbuilt oscillator. The output is available from pin 3.

This part does not really care because I will focus on how to use transistor as heat detector.

The writer wrote the following passage :
To test the working of the circuit, bring a burning matchstick close to transistor T1 (BC109), which causes the resistance of its emitter-collector junction to go low due to a rise in temperature and it starts conducting. Simultaneously, transistor T2 also conducts because its base is connected to the collector of transistor T1. As a result, relay RL1 energises and switches on the siren circuit to produce loud sound of a firebrigade siren.


My question:
Is this talk true, I mean the resistance between collector and emitter is small at high temperature. Can this circuit activate the relay to operate at a temperature of 30 degrees Celsius for example?

My friend who owned Machine chicken breeding (breeding) of the locally-made and wants to operate some internal parts when a certain temperature, can this circuit be used instead of the temperature sensor which is already not available (HERE). Thanks

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Hi Walid,
That is an extremely old circuit.
A reversed-biased silicon diode increases its leakage current as the temperature rises. A silicon transistor amplifies its own leakage current and can also be used as a temperature sensor.
Usually a diode or transistor feeds a comparator IC to switch something at a certain temperature.

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Thank you, I am very happy about your presence among us more than happy to answer, because I miss you and I intend to send a special message to you. I thank God that you are fine.

That is an extremely old circuit.

Possibilities in Canada very large, but in Palestine almost nothing, we are therefore interested in those circuits, which can be dealt with.
index.php?PHPSESSID=ea5c56fa44e6ae1b39d5
From the graph, I think it would be difficult to build a circuit to deal with temperature = 30
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