I need help and if anyone could help me I would appreciate it. I bought an MQ135 gas sensor and I downloaded the datasheet to know how to use it and found out that it has six pins 4 are used to fetch signals and 2 are used for providing heating current. After going through the datasheet I then connect pins 1 and 2 to VCC 5v and move to the other side where I connect pin 5 to the ground and pin 6 out and in between 5 and 6 there 10k variable resistor. After that, I connected a multimeter to read the output voltage I then turned on the power supply and placed smoke in front of the MQ135 sensor and I got an output volt from 0 to 1v or 0 to 2 but the problem was the MQ135 started to heat gradually which I found out that when I connect the pin 1 and 2 then the power supply current start to read from 0.11 on 5v which made the MQ135 to gradually heat. But when I tried it with 1 and 3 or did not heat but I got the same volt which is 0 to 1 or 0 to 2. Is it normal for it to heat? I haven't tried it before and this is my first time working on it. Any help will be highly appreciated.

 

The heater uses about 0.5W so I would expect it to get warm. If it is not warm it is not going to work correctly.

 

Certainly it must get warm to function correctly. It s the chemical reaction of oxidizing the sensed material that produces the change. I have a patent on an industrial device that uses those sensors.