The SB-15 is a tin dioxide semiconductor gas sensor which has an excellent performance in ropane/butane detection. The eatures are: high sensitivity, ow sensitivity to noise gases, uick response speed, strong oisoning resistance andsignificant low power onsumption design (120 mW). Tructure as sensitive   aterial s a mini bead type and aheater coil and electrode wire areembedded in the element. Thesensing element is installed in themetal housing which uses doublestainless steel mesh (100 mesh) in the path of gas flow. The mesh is ananti-explosion feature (Fig 1). Operating conditionsFig 2 shows the standard operatingcircuit for this model. The change of the sensor resistance (RS) is obtainedas the change of the output voltageacross the fixed or variable resistor(RL). In order to obtain the bestperformance and specifiedcharacteristics, the values of the heater voltage (VH) circuit voltage(VC) and load resistance (RL) must be within the range of values given inthe standard operating conditions

shown in the specification table onthe next page.Sensitivity characteristics

Fig 3 shows the sensitivitycharacteristics curves of the SB-15(typical data). Sensitivitycharacteristics of the FIS gas sensorsare expressed by the relationship between the sensor resistance andgas concentration. The sensorresistance decreases with an increase of gas concentration based