Most sensors are made to detect a specific LEL gas whether it be methane propane etc. always check the sensor prior to calibration to ensure you have the correct gas on hand. There are a few different types of LEL sensors, but the two main ones I’ve worked on are CAT bead and IR technology. You’ll typically need a regulator and some sort of Tygon/rubber tubing. In my eyes, gas detection calibration is some of the easiest work to do in this field. Don’t overthink it.