I’m looking at the blog post, and I’m not sure whether I’ve found a tiny typo, or I’m not understanding something about how the fix is meant to work.
Under the heading “Update #2 (29 October 2024)”, there’s a written version of an algorithm. The value PM2.5_calibrated_low is calculated using two constants and the PM0.3_count. In the case that the result of the calculation is below 31, it will be is carried forward, replacing the PM2.5 value.
Is it intentional that the sensor value for PM2.5 is never used in this case, only the PM0.3? If so, why does this work?
Yes, this is intentional. The PM2.5 raw readings of some batches are lower than expected. Often they report 0 ug/m3. Unfortunately, this happens when the actual PM2.5 is indeed 0 ug/m3, as well as when the PM2.5 is supposed to be higher. This means that based on the raw reading of 0 we are unable to tell whether it was indeed 0, or whether this value should be corrected. That’s why we decided to do the workaround via the PM0.3 count instead.
hi. what to do in case I cannot read the sensor serial number (it has gotten white due to weather conditions)? I have tried setting all three epa corrections, but still results provided are too low compared to public available aqi sensors in my city.
Please contact our support through our website together with the serial number of your monitor (not the PM module). We can then have a look at your data.
Hi @Achim_AirGradient, I have one of the affected devices (PMS5003-20231218 batch) and the dashboard update has a weird interaction with this issue:
The issue is that, when the PM.03 values are super low, they tend to come back with a brief “spike” before settling back down to low values.
When I first reported this issue, the behavior on the PM2.5 setting was that it would show – temporarily and then go back to zero.
Now, on my dashboard, I am seeing large spikes of PM2.5 as well. I believe this is because the correction formula uses the unreliable PM.03 value instead of what the PMS5003 is reporting natively?
I’m wondering if 3.1.11 will come with other fixes that will remedy this, or if it’s time to give up on the PMS5003 sensor in my unit and replace it.
The air was pretty clean prior to 7PM and you can clearly see the weird “spiking” behavior. I think 7PM was about the time I cooked dinner, which resulted in the levels rising enough for the numbers to look more normal.
It’s definitely unusual. What air purification system do you have in your house? Is it only HEPA filter or also some kind of electrostatic / ionisation system? Maybe there are some interefences from other systems. If not, it’s probably a broken sensor.
The room where the unit is has a Winix 5500-2 which includes HEPA filter plus something they call “Plasmawave,” which I believe does ionization. However, I usually have that ionization feature turned off. Beyond that, the room seems fairly well-sealed from outdoor air (based on the significantly escalated CO2 levels when two people are sleeping in the room).
I’m leaning towards the broken sensor explanation myself. You had mentioned before that the PM5003 seems to result in read errors with low PM concentrations, and I see that 3.1.9 “Fixed PMS read errors in low concentrations” according to the release notes.
I think the difference with my PMS5003 sensor is that, after the read errors occur, the PM0.3 levels “spike.” I don’t think I’ve seen anyone else report this particular issue on the forums.
I have seen before very strange behavior in connection with Ionisation equipment. Would it be possible you switch that function off for a few days and see if that makes a change?
@Achim_AirGradient, I will try it with that function disabled for a few days. It doesn’t seem to have an effect if it’s disabled overnight (the “sleep” mode on the air purifier does that automatically) but I don’t think I’ve kept it off for more than 24 hours. Will report back!
@MallocArray, I actually did enable the setting in the web app. That’s when I noticed that the strange errors from my PM0.3 sensor affected the PM2.5 readings.
Without the correction enabled, it would almost always be at 0 to 1 unless the air quality outside was particularly bad and got into my home (e.g., regional forest fires). With the correction enabled, I was getting random spikes up to 50 (and I have a hard time believing that the actual PM2.5 level in my room would go from 0 to 50 to 0 within a span of 20 seconds).
I have the same issue with the pm0.3 count jumping to a very high number, often above the number registered on the outside monitor. Weird given that there is no movement in the room, the windows are closed and the air purifier is off.
@eugene@rpirsc could you please share the serial number on your PM sensor (not the AirGradient monitor). Especially the date stamp on the serial number.
Then we can have a closer look in our test lab to see if we can reproduce this.
Hi @Achim_AirGradient, the serial number on my PM sensor is PMS5003-2023121807159. I can also report that disabling the ionization function on my air purifier ~2 days ago doesn’t seem to be changing the behavior.
Once I apply the correction, should I expect the correct PM2.5 values to appear on the display of my AirGradient? I’m currently just seeing 0 on it, but the dashboard shows the actual correction.
