Saturday, April 27, 2019

CO2 meter

We hear so much about CO2 these days.

I want to measure indoor or outdoor CO2 concentration at a reasonable cost (~$100).

These are first reactions to HT2000, a portable recording CO2 meter which also measures temperature, humidity and dew point.

My HT2000 came from product ID: 1258981 "USB Carbon Dioxide CO2 Data Air Temperature Logger Humidity Meter Monitor LCD" US$99 and arrived promptly in a little over a week. I noticed shipping was from a depot in Mississauga.

I think what I have is an unbranded generic version since I see others like it when I search "CO2 meter". Mine is one of the cheaper ones.

The case is bigger than I thought it was going to be, about 5.5"/14cm long and about 1-1/2"/4cm thick. Case is not sealed or waterproof. It can't be, air has to move through it. You wouldn't carry it in a pocket easily, nor would it work very well in your pocket.

HT2000 needs to be out in the open on a table, desk or dashboard, for example. I've concluded that HT2000 is sufficiently sensitive to CO2 that if I hold it at arms length in an enclosed space, my own body expelled CO2 will affect the measurement.
My CO2 aura in effect.

My HT2000 arrived in a clam shell carrying case with manual, software CD, USB cable and charger (mini-USB, not micro). Under a cover on the back holds 4x AA conventional batteries. I found run time of about a day on the internal batteries since HT2000 is hungry. Draws about 1.1 watts from AC when plugged in.

I tried to measure actual battery pack current after getting inside the unit. The current drain is very peaky rising to almost 2A at 6 volts then dropping then rising. It was impossible to get a stable reading from my digital amp meter. I will try again later with an RMS reading milliamp meter. HT2000 seems pretty demanding on batteries. There is a hole in the side of the case for what might fit an optional DC input but there is only USB power or internal batteries on mine. When I plug in USB power it switches from battery but there is no indication on the display.

[click any pic to enlarge]

The manual I received is in English. A challenge to read but all the right information is there. I found another version of the manual online by searching "HT2000 manual". Between the two and fiddling with the unit, I was able to figure it out.

On power up, the unit performs a short self test and the display shows all digits and characters, some of which seem to be for other versions of the instrument since I never see them lit during use except at self test?

After self test, the unit counts down seconds from 30 to zero to "preheat" the sensor as explained in the short manual.

When I first started the unit at my desk, the CO2 numbers were over 1500ppm and I was a bit concerned that the instrument was faulty. I had been looking at it closely before starting it up for the first time. When I put it at arm's length and left it alone for a while, the number dropped to a level more like the first picture 600-800 ppm so it was quickly apparent that it was responding to me!

There are alarms for CO2 and the other measurements that can be set in the software. The default alarm for CO2 is 2000ppm. I can reach that level easily by just blowing at the instrument from a foot away! The alarm is a loud constant tone that continues until the level drops or the unit is switched off! I am glad that it didn't alarm the first time! It was close.

Yesterday was a beautiful Spring day so I spent the afternoon cleaning up winter debris in the back yard.

Outside, HT2000 gave readings from 350 to 400 ppm, about what it should be. I was burning wood scraps in a fire about 5 meters away from where this picture was taken so there may have been some effect from the fire? It seemed to me that when I got close enough to the unit to read the display, CO2 started to rise but I can't be sure of that! There was gusty wind.

The reading update frequency is changable in the software. I currently have it set for 1 second update. This is a different setting from the recording frequency which I have set for 1 minute.

The software has two main sections. The Communications section lets you connect, setup and read the instrument via USB. I am in the Data section in this picture showing the results of my first overnight test recording of CO2 concentration and temperature in my bedroom last night.

The data is scroll-able on the left side and graph-able on the right. The settings for the graph can be changed.

I found the Data view a bit restricted so tried the data export to a spreadsheet and graphed the results from there. I gave the Temp its own axis so it wasn't constrained down at the bottom of the plot.

The measurements are every minute, there are 890 measurements. #1 is 15:48 when I installed it upstairs, pushed the record button and left the room. There is no one else upstairs. You can see the CO2 and the temperature settling over the next 100 or so measurements. About #100 the CO2 goes up slightly but the temp keeps dropping slowly. I think the furnace may have started and stirred the air in the house? The windows are all closed. It is still heating season here.

About #342 (21:30) I enter the room to sleep. I don't close the door. A bit later, the furnace shuts down to overnight temperature. Temperature starts a slow decline and that's MY CO2 increase in the room! I think I can see that the variability (the envelope?) of the CO2 data also gets larger.

Around #784 (5:00 morning) the furnace starts to warm the house. Temp abruptly starts to rise and CO2 falls abruptly as my CO2 is spread around the house.

Around #852 (6:00) I rise and move around the room before exiting. I leave HT2000 in the room for another hour before taking it downstairs and downloading the data.

A look inside the unit shows the IRM300SS sensor from SemeaTech. [the gold thing at the top]

There are two versions of this sensor. This one is accurate to 5000ppm but has a 5 year life. The "non-SS" version measures to 2000ppm but has a 10 year life expectancy. These are nondispersive infrared sensors (NDIR), specifically for CO2. A "simple spectro graphic sensor" using IR light which is tuned to a specific gas.

There is one peculiarity regarding the batteries. When the batteries are low, the unit will start displaying 0 ppm. Before that occurs however, the display will start flashing what looks like "Bar" every few seconds. Really means "Bat" which was confusing the first time and alerted me to the short battery life.

To prevent problems with recordings, rely on the batteries only to move the unit when it is not recording. Or you can take measurements without recording when you have fresh batteries. Plug the unit into USB power for recordings.

Once you push the Record button you MIGHT see the REC record indicator flash ONCE briefly. It's on the left side middle of the display. From then unit is recording and you will see REC flash BRIEFLY every time it makes data. If you have recording set to once per second, you will see REC flash every second. If you have the duration set longer, you may not see it flashing easily.

One more thing: CO2 must propagate into the sensor and this takes time. There is no fan. You can speed reaction by moving the unit around in the air causing airflow through the case. There are slots in the top back and sides for airflow but it's passive. Nevertheless, unit does respond to changes in seconds. It just may take minutes to reach some equilibrium.

I purchased HT2000 because it looked potentially useful. I am not sure yet what specific uses it will find with me. It is always good to be able to measure. Do you need one? I have no idea but perhaps you now know more to help you decide. If you do find cool uses, let me know.

Thank you for your interest.

George Plhak
Lions Head, Ontario, Canada

You may also like my radon test

As is my custom, this is not a paid review nor do I receive or solicit any product in return for writing. I am not selling these products. Just ideas. I don't get a commission. I don't show ads. I don't have a fundraising or patreon page.
I write in the hope that this is interesting or useful to you.
If you would like to show support for my independent work,
please consider commenting or buying one of my books? Thank you. George

update June 24 2019 CO2 in my home varies over a wide range. This is a low I saw June 10. I haven't noticed a pattern.

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