I have myself a MG-811 sensor with a sandbox electronics board for signal conditioning (http://sandboxelectronics.com/store/index.php?main_page=product_info&cPath=66&products_id=197
) and I have mixed feelings about it.
- It is not too expensive ($54, I think) considering that CO2 gas sensors are not the cheapest gas sensors.
- It needs heating, so there is a DC input on the board. This heating circuit makes the sensor use too much power for batteries.
- Heating time. I am experiencing long heating times until readings are stable. Normally, as soon as you turn it on, measures are very high. Slowly they go down to the real level. But for me, this is taking up to 10 minutes. I don't know if it is a problem with my unit or it is the usual behaviour.
- Calibration. On the specs, you can read that every unit must be calibrated
. You must calculate 2 voltages. One is for fresh air, which is ok, you can run the sensor for a period of time at your window and look for the voltage corresponding to smallest ppm concentration . BUT
you need a second calibration point with 1000 ppm gas
. This gas is quite expensive (a kit for 20 calibration costs $600).
So, by the moment I am running the device without knowing how accurate measures are.
I am seriously considering buyin a ndir CO2 sensor, which only needs fresh air calibration. Probably Cozir ambient.
Hope this helps