Have you searched on sensors that are available? Thermal conductivity detectors are one type you might be able to make. That is, if the majority of the gas present is air, a little butane will change its thermal conductivity. A heated wire will change in temp, and that can be measured by resistance. See: Thermal conductivity detector - Wikipedia, the free encyclopedia
There are commercial, solid state devices that might be more suitable to your application.
Is your project to make the detector or to make a device for detecting leaks. If it is the device, then I woudl just buy a commercial detector. If it is to make the detector per se, the TC or flame ionization are easily doable. Have you done any search of the Internet on this subject?
my project is to make a detector . i have already try some sensor which are sensitive to LPG or butane gas. I have search bout this topic on internet and now already completed almost half . But i need gas concentration meter to improve my detector, seems like quite difficult to get it in market
ya...i know the data sheet show us the plot
but i need it to measure the concentration of gas appeared because i plan to output the value of concentration to my detector display if possible
ya...i know the data sheet show us the plot but i need it to measure the concentration of gas appeared because i plan to output the value of concentration to my detector display if possible
Perhaps if you tried to rephrase or expanded upon that (bolded) part of your question, it would be clear why that sensor is not giving you the result you need.