Characteristics of TGS-813
The TGS-813 is basically a sintered type of semiconductor primarily made up of tin dioxide (SnO2). When it comes in contact with any gaseous element, its internal resistance immediately drops.
As the concentration of the gas rises, its resistance drops proportionately and can become as low as 20 times to its normal value.
The TGS-813 is rated as one of the most reliable and longest lasting gas sensors.
As shown in the diagram, it consists of six terminals, two of which are connected to a heater coil, while the other four contacts are wired across a gas sensing resistor.
To initiate the sensor, a preheating of the heater coil is necessary. It may take approximately three to five minutes before the actual sensing of the gases can take place.
The electrical parameters of the sensor are as follows:
As discussed above the heater coil needs preheating for about five minutes; to do this a 5-volt DC supply is applied across it.
The resistance of the heater coil is around 30 Ohms, and thus the current required is quite significantly high, about 200mA.
Ideally a voltage regulator is recommended for this purpose. The versatile IC 7805, which should be able to supply 5 volts at 1 amp maximum current, can be used,.
The dynamic resistance of the sensing element of TGS-812 in normal conditions, i.e. in clean air, is approximately 50 K and may fall to about 3 K in the presence of a gas around it.
Even a puff of cigarette smoke when released from a distance of about 3 meters would make its resistance fall significantly.
You may refer to the shown diagrams in its DATASHEET to know more regarding the technical data of gas leakage sensor (TGS-813).
ImageTGs-813 credit : http://www.professionalequipment.com/product_images/G278_product.jpg