Last modified July 8, 2021
This question about reliability, precision and accuracy of home CO2 meters, appears repeatedly and, the truth, I felt that it was time to write a few lines about it because there are very little informed opinion on the internet and it can be difficult to know the truth among so many opinions.
Although the answer is not that simple, I will start by saying that yes, that home meters are just as reliable, accurate and precise as commercial ones (be careful, the range we are talking about), although there are always some nuances. Next, I will reel off why.
DISCLAIMER OF LIABILITY
I have wanted to publish this article for a long time, without daring at all.
Of course I will start by saying that this is just another opinion, my informed and honest opinion. I hope nobody gets on top of me ...
I don't have to be right, I have simply dedicated myself to writing what I think about this matter.
I will not be held responsible if my opinions cause a new political conflict, world disorder or the zombie apocalypse.
I am aware that I am getting into a Marshy ground, where there are important economic interests of a booming industry. I'll accept all kinds of criticism in the comments, as long as they're polite, though I will prefer the constructive ones.
This article is pending review, differentiating between reliability, accuracy and precision and making their difference clear.
- 1 The reliability, precision and accuracy of a homemade meter
- 2 What is a CO₂ meter like?
- 3 What does a commercial CO₂ meter provide?
- 4 And now the landlord. What can go wrong (or right)?
- 5 User testing
The reliability, precision and accuracy of a homemade meter
The first difference we find between a user who has a commercial meter and one who has a self-made meter is that you know what materials you have built it with.
There are many cheap (and not so cheap) commercial meters that they look very good, but have very bad sensors that are not valid for our purposes when we measure CO2 in the environment. Sensors must be NDIR, non-electrochemical, and other types.
When you build the meter yourself you know that the sensor you use is NDIR and not another type.
Keep in mind that, unless you compare it with a € 10,000 meter, the NDIR CO2 sensor that the "professional" meter will carry is exactly the same as the home one (or worse, because the Senseair S8, which we are using is one of the best, within "What you can afford", and there are many commercial meters that use sensors terrible). In addition, this CO2 sensor is already factory calibrated by the manufacturer, so you should check acceptably well from the first moment and improve with the days thanks to its automatic calibration system.
I bet the vast majority of manufacturers of commercial CO₂ meters are not calibrated by their manufacturers one by one, but simply rely on the calibration of the sensor manufacturer, as we do. The difference is that there are many other CO2 sensors that are very poorly calibrated from the factory.
Sensors, over time they are decalibrating (Also the meters of 200 or 300 €) and that commercial meter for which you have paid 100, 200 or 300 € is decalibrated just like yours, so its precision in the measurements will be the same as yours and will depend exclusively on the care you put when calibrating it (the same as yours, homemade, as the one for € 300).
Here we can talk about something important, and that is "The education" (information and knowledge) that most of the people who buy a commercial sensor have is little pulling to null (not to mention the rickety manual you would normally get with the commercial meter), while A user who builds his meter with love, following a tutorial like the one in this blog, has the concern and desire to learn and does not have a rickety manual, but a whole blog with a lot of information about it and a community of users who participates, helps and contributes their knowledge and experiences.
How many manuals of commercial meters correctly explain to the user how to calibrate the device?
Notice that the only commercial meter that I have bought in my life, of which there is an analysis in this same blog, came badly calibrated and measured high over 150-200 ppm and continues to measure high because You don't even have a procedure to calibrate it, to trust commercial meters!
Definitely, the home CO₂ meter will measure very well if it is based on a good project (exactly the same as the € 300 commercial) but the exact CO2 concentration will depend on the actual one at the time of calibration (same as in the 300 €) and like, both one and the other, you have to calibrate them from time to time, you will never know the exact CO2 concentration unless you have it calibrated to a laboratory (both one and the other).
What can we expect in terms of precision in the measurements, both in one case and in another (and as long as the calibration is done correctly)? 100 ppm? It seems enough to me! When we talk about health and CO₂ (or Covid and CO₂) it's not those little differences that make the difference.
What makes the difference is that some users live with very high concentrations of CO₂ without even suspecting it And it is having a CO₂ meter that opens their eyes. Some users have said in the Telegram group (come over and see it) "I have built the meter, but it does not work well, it shows more than 1000 ppm and it does not stop going up" to realize that those figures they were correct. Not already 1000 ppm, but it is easy to have 2000, 3000 ppm and more, if we neglect the ventilation (myself in the room where I work, if I do not ventilate, at the end of the day I am always above 3000 ppm).
What is a CO₂ meter like?
A CO₂ meter is a device used to measure the concentration of carbon dioxide in the air and that consists of a detection sensor, electronic components and firmware, or computer program, that makes these three parts work.
Really CO2 measurement is performed by a single component, the CO₂ sensor, and the rest of the components and firmware only works for that sensor to work and tasks related to the use of those readings.
When I say "make that sensor work," I mean things like:
- Provide you with feeding correct
- Yes there are drums, keep it charged and in optimal condition
When I say "tasks related to the use of those readings" I mean things like:
- Allow us to see the measurements in some way (a screen, for example). Can you imagine a meter that had no way to see the measurements?
- Allow the user to communicate with it (turn it on, off, calibrate it, configure alarms, if it has them, etc.)
- Various things such as self-tests, measure and show us the temperature or humidity (in the models that have these functions), etc.
Really the precision of the meter will depend, fundamentally on the following things:
- Of the sensor used (there are better and worse)
- Of the quality of the electronics (that the sensor supply is stable and clean)
- From the user: That he knows what he is doing, that he calibrates it properly and gives it good use, maintenance, etc.
In the image below you can see the inside a commercial CO₂ meter, Kecheer brand (although it is also sold under other brands such as Baugger, KKmoon, KKTECT, S SMAUTOP and Brisunshine). As you see, it's not very different from ours. In this case it uses a CO₂ sensor from the manufacturer Honeywell, but this same meter They also sell it with the Senseair S8 sensor that we usually use in our project (and probably with other sensors).
What does a commercial CO₂ meter provide?
If we think about it, a commercial meter provides the following advantages:
Everything ready for use
Normally with a commercial meter all you have to do is buy it, open the box and press the power button.
This, which in principle is very good, has an important disadvantage: the user has no idea how that device works and, therefore, it is very likely that it is misused and not properly maintained.
Many users do not know that their meter must be calibrated by themselves from time to time to provide correct measurements (and there are even commercial meters that do not have no type of calibration, As the DM306 meter that I analyzed here).
Clear instructions (or not?)
Normally, a commercial quality meter comes with Clear instructions, even if it's in English, most of the time.
Clear instructions, often means instructions short and scarce without entering any point that the user may find a complication.
Brands are very concerned that their product is presented as easy to use. Often this means that the instructions will disregard warnings, cautions and procedures relatively complex that can give the user the appearance of difficulty.
The above is about quality commercial CO2 meters, but what about non-quality ones?
The market is flooded with Chinese origin meters of a very low quality, and this is reflected in the manual. On many occasions they are terrible translations into English, which leave a lot to be desired. When the translation is into Spanish the result is usually even worse, having many manuals that it is better not to read.
An aesthetic product with a good finish
Here we have an important point in favor of commercial meters.
A meter enters through the eyes and most of the people they distrust a meter with a homemade look, thinking that their measurements cannot be of quality, confusing the part for the whole.
To the fans, there is no doubt, what costs us the most is to give our projects a good finish. No matter how hard we try, we can't compete (with some honorable exceptions) with commercial terminations.
Even the most basic and cheap commercial CO2 meters look good (regardless of whether their construction materials look more or less cheap). No hanging wires or holes that are not perfectly round will be visible, and they usually have a good lettering.
The manufacturer's warranty
The manufacturer's warranty, I said? Sorry to laugh!
There is no doubt that there are manufacturers that ensure a exceptional service, with a service quality aftermarket (selling your product at a price consistent with this service).
But most of the time we will not have this quality service.
When we talk about the lower-middle range of commercial CO₂ meters, which is what most users buy, what we find are very low-quality Chinese products that, like so many other low-priced Chinese products, are intended for give the minimum and fail to the minimum. They are intended to be cheap.
CO2 meter approval
To be able to sell a CO2 meter in Spain (or anywhere in the European Union) it is necessary that it complies with European regulations, and shows the CE Marking. So that, in theory, if we buy a CE meter in Europe it should have the CE Marking (in practice I have seen Many commercial models of CO2 meter without CE Marking).
Does the CE Marking mean that the meter is going to be more accurate, accurate or reliable than a homemade one?
Well the answer is no.
To understand it, we are going to reel off this aspect to see what must a CO2 meter meet to obtain CE Marking.
Although it is a device that measures, it is not necessary to comply with the directive 2014/32 / EU that regulates the marketing of measuring instruments.
As it has no moving parts, it is not a machine either, so directive 2006/42 / CE, which is the Machinery Directive, does not have to be applied.
Once we have excluded the previous rules, we are left with this type of device being in the electrical and electronic equipment category.
Electrical and electronic equipment must apply the following standards and directives:
▪ Directive 2014/30 / EU of Electromagnetic Compatibility (CEM).
▪ Directive 2014/35 / UE Low Voltage Electrical Equipment (Electrical Safety Directive).
In addition, it may be necessary to comply with the Harmonized Standard UNE EN 61010 of safety requirements for electrical equipment for measurement, control and laboratory use.
As you can see, of everything a CO2 meter needs to comply with the legislation and to be able to sell (and in its case manufacture or import) in Europe, None of these things do anything to make a commercial meter more accurate, accurate or reliable than a homemade one..
It must also be taken into account that the components we use (at least those corresponding to the tutorial on this blog to build a homemade CO2 meter) They are already approved and have the CE Marking, which indicates that said components have the corresponding tests, tests and documentation regarding their electromagnetic compatibility (not producing interference) and that of low voltage electrical equipment (being a safe component).
Clarified that building a device with components that have the CE Marking does not automatically grant the CE Marking to the built equipmentTherefore, we could not sell them as commercial equipment without first obtaining the CE Marking of the product (with its corresponding laboratory tests, technical documentation, user manual, etc.).
And now the landlord. What can go wrong (or right)?
Actually, most home CO2 meters they are quite simple devices:
- They receive the measurement from the CO2 sensor and
- They show it to the user in some way (as the sensor sends it)
In principle the meter does nothing else, does not manipulate the measurement or have to calculate anything in particular, however, there are things that can go wrong ...
There are two main types of problems that can arise with a home meter: those of software and those of hardware.
Although most meters do not have to interpret the measurements provided by the CO2 sensor, nor do they have to modify them at all, problems can occur.
- A bug in the firmware that modifies the measurement before showing it to the user
- An error in the programming of the communication with the CO₂ sensor that makes it not "understand" what the sensor is sending and take one thing for another
Both in one case and another I think the solution is simple (and it is exactly the same as you would use with a commercial meter, which is not without these problems either): Choose a homemade CO₂ meter project well documented, built by enough people, with good results, and reputable.
Here, the range of problems may be somewhat greater. Basically we can find the following problems (of the project, not of the assembly that each user does, which could give other problems if he is careless when doing it):
- Power failures. The most common and that if you follow a good tutorial you should not suffer (and not only that it teaches you to avoid them, but it teaches you to anticipate, prevent and identify them).
Did I say the range of bugs was greater? Well no. I lied. What happens is that feeding problems are not uncommon (not in commercial meters) and can be a problem.
Normally in the instructions of a project worth its salt, they will talk at length about food. You just have to read and follow the instructions. If the project does not speak to you at length about this matter, it is better that you do not take it seriously and look for another.
If you have to pay attention to one thing in particular, meter projects that include rechargeable batteries:
It is not easy to design the stage that supplies a meter that can be used both connected to current and with batteries (when it is one or the other it is not so critical). I guarantee that more than 80% of the maker projects have problems in the feeding stage (also many commercial ones).
As in the case of software, I think the solution is simple (and it is exactly the same as you would use with a commercial meter, which is not without these problems either): Choose a homemade CO₂ meter project well documented, built by enough people, with good results, and reputable.
Some of the users with access to professional meters have made some very interesting measurements. Below, I include the data of some of them, with the permission of the users:
You have used a professional CHAUVIN ARNOUX CA 1510 meter. It is a CO2 meter, not just commercial, but a professional and certified CO2 meter, which costs more than € 400.
The user has performed two rounds of measurements with the two gauges simultaneously (the Chauvin Arnoux and the Senseair S8 LP eMariete Gauge with sensor). These are the results, in his own words:
During the day
«On air for 1 hour: S8 / CH 412/426. Empty room: 656/665. Room occupied by me with closed door, evolution in half an hour: 850/868, 948/939, 1032/1020, 1063/1080 (on some occasions the Senseair scored higher). Empty room again: 726/732 and now with the door open, 798/793, the data from the photos from 10 minutes ago 802/811 »
In the evening
«Comparing during the night, very similar measures, that is if the Chauvin is« certified », the Senseair too, and even better, because it reaches lower values abroad (as I put above, I am in an unpopulated area with a small city than 8000 inhabitants below, at the bottom of the valley, 1 km away). Consulting both graphs, I report the data every hour in a room of about 25 cubic meters, with a person sleeping with the door and windows closed: S8 / CH. At 3 1371/1345, at 4 1686/1667, at 5 1833/1882, at 6 2024/2060, at 7 2165/2191, at 8 2335/2352 at 8.50 (maximum) 2374 / 2437, the window opens ajar at that time, at 9.30 534/643 and the final minimum at 10: 431/452. »
If you have also been able to do tests with a home meter and a commercial one, tell me in the Telegram group to include it!