TOXIC_GAS_DETECTOR

Published:2009/7/1 0:41:00 Author:May | From:SeekIC

The major device in the circuit is SR1(a TGS812 toxic-gas sensor manufactured by Figaro Engineering Inc.) The gas-sensitive semiconductor (acting like a variable resistor in the resence of toxic gas) decreases in electrical resistance when gaseous toxins are absorved from the sensor surface. A 25,000 ohm potentiometer(R5) connected to thesensor serves as a load, voltage-dividing network, attd sensitivity control and has itscenter tap connected to the gate of SCR1,When toxic fumes come h contact with thesensor,decreasing its electrical resistance,current flows through the load (potentiometer R5)．The voltage developed across the wiper of R5,which is connected to the gate of SCR1,triggers the SCR into conduction。With SCR1 now conducting,pin 1-volt Supplyfor the semiconductor elements of the TGS812 h1 spite of the suggested 10 volts,thusreducing the standby current．A 7805 regulator IS used to meet the 5-volt requlrementfor the heater and semiconductor elements.



Reprinted Url Of This Article:
http://www.seekic.com/circuit_diagram/Measuring_and_Test_Circuit/TOXIC_GAS_DETECTOR.html

Print this Page | Comments | Reading(3)