MQ136 Sensor Question

Using Arduino Sensors
1

I tried searching the forum for a similiar issue, so hopefully it hasn't been addressed already.

I'm trying to get an MQ136 sensor calibrated for a project at work. I bought the SainSmart breakout board to simplify what I need to do, but am having an issue with responsiveness. I've performed a burn-in time of over 48 hours, per the data sheet instructions on the SainSmart page. I'm currently using an external 5V 1A power supply for the heater, as the instructions I've read make it unclear whether or not the power output abilities on the 5V arduino pin is enough. The Arduino is grounded with the board, and I am getting stable results.

When I expose the sensor to a known concentration of H2S, the sensor response. However, the issue is that it takes a very long time, up to an hour, for the sensor to return back to it's normal, pre-exposure, resistance/output. I've tried blowing on the sensor to see if I can 'clear' up any gas, but that doesn't seem to be the issue.

Someone at work suggested that the sensor might simply be damaged or shorted out. But before trying a different sensor, I figured to make sure it's not a simple mistake that I'm making. Any leads on posts or information to read, or suggestions, would be greatly appreciated.

2

Which H2S concentration did you use for the calibration? Was it H2S in N2 or where any other gases present?

3

It's standard calibration gas, H2S in N2. I've used both 25ppm and 40ppm. As it should, it does give a higher response to the 40 ppm gas.

4

What you did sounds ok. The sensor is specified up to 100ppm, therefore 25ppm and 40ppm are reasonable values for calibration. Did you preheat the sensor for 24h as recommended in the data sheet before using it?

5

Ya. It's been even longer now. The first time I tried it, I hadn't done the burn in, and I was getting random and sporadic results. Now, the output is very stable.

For instance, right now I was getting an analog input of 14 mV and when I exposed it to 40ppm gas for a brief second, it went up to ~122mV. In 40 minutes, the reading has gone up to about 141mV. It is now stabilized at 141mV. Usually, in a few hours, the reading is back down to the 14mV level.

6

An update for anyone who might be interested:

I simply got a new sensor, and with the same hook-up and same settings, the new sensor responded as it should. The sensor must have been damaged or have been defective.

7

I'm incorporating this same sensor board into a project and would appreciate a peek at your code if you don't mind sharing.

8

Hi sorry i am newbie
Wow it's so cool, how to calibrate MQ 136 sensor in the code program?
can you share your project please?

Thanks