SainSmart MQ-131 Ozone Sensor

I am working on an ozone project and I have a number of the SainSmart Sensor modules. I have done the 24 hour burn in and get good stable readings from the sensors to my Arduino. I have been trying to calibrate the sensors using an ozone generator and a 2B Technologies Ozone Monitor.

The problem that I am having is the I am generating ozone and the readings go from a normal ambient reading of approximately 17 ppb to around 25,000 ppb, but my arduino readings go from a stable 37 and drop to maybe 15-17.

I know that there should be readings available between 0 and 1024, and I have seen readings as high as 994 during warmup. My question is how do I broaden the range of readings? Basically right now one unit of the arduino reading is equal to between 1000 and 1500 ppb.

Can I get a better range of values by changing the ciruit or do I need to use the mapping function in the Arduino code?

Does anyone have experience working with these sensors? I do not see very many posts that provide much more information than the data sheet. The data sheets are crap on these things as well.

Normally the value goes up, because the sensor has a lower restance with a certain gas, and the voltage over the load resistor increases. This one is the other way around. You need a higher value for the load resistor and the voltage over the load resistor goes down. Did you read a few datasheets ? Try a load resistor of about 50k to 200k (or more). Some MQ-131 require 6V for the heater.

Do you know how sensitive the sensor is ? It is extremely sensitive, it can already detect 10 ppb. Other MQ sensors are in the ppm range.

Added: Now I see the module. I has a adjustable load resistor. Do you know the value of that adjustable resistor ? Perhaps they put the wrong one on the module. Can you adjust the resistor so the default value will be around 1000 ?

Thank you,

I have been out of town working on another project for a couple of weeks but I have found that my beginning values are much higher with added resistance. I used a 22k ohm resistor and have now got readings that are stable at around 970 compared to the 30 or 40 it was at.

I found that on the module is a 2200 ohm 3362 trimpot and have found the best results with it set exactly in the middle of the range.

I am going to get back in the lab this week and use the ozone generator so that I can see if I get the range I am looking for or if I am just beginning at a higher value.

Looking at the data sheet this sensor has a range from 10 ppb to 2 ppm. This is suitable for my needs since the EPA air quality index runs from 0 ppb to 604 ppb (0.604 ppm).

I just need a bit better resolution.