These are of 3 differet types

Flame Electrode Sensor

Applications : Gas oven / Gas Stove / Gas Heating

Material : Alumina with alloy steel

Thickness : 2 mm

Photo Voltaic Flame Sensor

Principle: Photo Voltaic

Material : Alloy Steel

Sensing Range : 400 mm

Photo Resistor Flame Sensor

Principle : Resistive

Resistance : 5 K to 10 K ohms

Max Operating Temperature : 70 degrees