Sensor Selection: CO2
I’m very interested in how much CO2 collects in the lab, particularly during open-house nights so a CO2 sensor is a must. CO2 sensors don’t come cheap though – a search on digikey indicates that I can pay hundreds of dollars for a single sensor module. After doing some poking around, I found CO2meter.com, which listed two promising candidates at prices that might actually be affordable. The first is the SenseAir K-30 0-10,000 ppm CO2 sensor for $65.00. The second is the Gas Sensing Solutions COZIR 0-10,000 ppm sensor for $109.00. Both of these sensors are solid-state – they make use of Non-Dispersive Infra-Red sensor technology, which means they won’t wear out as quickly as an electrochemical sensor. COZIR sensors come in measurement ranges of 0-2,000 ppm, 0-5,000 ppm as well as the 0-10,000 ppm sensor, but I’ll probably skip the lower range sensors for a 0-10,000 ppm sensor. While atmospheric CO2 is only around 400 ppm, some comments on the forum post here suggest that a small, poorly ventilated space with many occupants will easily reach 3,500 ppm CO2 or higher. Hacklab isn’t much bigger than some living rooms, and we will sometimes have a couple dozen occupants, so I want to be able to measure very high levels.
The SenseAir K-30 module features are:
- No case/packaging.
- Measurement range of 0-5,000 ppm “within specifications”, 0-10,000 ppm “total”.
- Accuracy of +/- 30 ppm, +/- 3% of measured value.
- Outputs readings every 2 seconds.
- Serial communication with I2C and MODBUS protocols. It also has analog voltage output for CO2 indications.
- The sensor has embedded calibration code which assumes that the ambient CO2 concentration is 400 ppm most of the time and corrects accordingly once per week. I suspect this may cause trouble for me at some point if I can’t find a way to turn it off.
The Gas Sensing Solutions COZIR 10K ppm module features are:
- Finished case with 3 mounting holes.
- Measurement range of 0-10,000 ppm.
- Accuracy of +/- 50 ppm, +/- 3% of measured value.
- Outputs readings every 0.5 seconds.
- Serial communication as well as analog voltage output for CO2 indications, though it’s not clear if you have to request the analog output functionality specifically or if it ships by default.
- According to a datasheet sent to me by GSS, the COZIR sensor comes factory-calibrated and has an auto-calibration function to correct for long-term sensor drift. Again, I suspect this may cause problems unless it can be bypassed.
Right now I’m leaning towards the SenseAir K-30; it’s low-priced, accurate, and has a wide variety of communications protocol options. The readings only come in once every two seconds, but for monitoring Hacklab’s atmosphere I don’t really require the high reading rate of the COZIR sensor. I also don’t need a finished housing since I’ll be designing my own. Ultimately I think both sensors would work quite well, but right now the K-30 is looking like a very solid option, particularly if you consider cost as a major influencing factor as I do.
I’m in the process of trying to obtain one of the K-30 modules to hack on, and I’ll write an update about working with the sensor module when I’m able.