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I have not replaced the sensor all this time and, old as it is, seems to be working. My conclusion is there must be some source out there that is producing intermittent bursts of VOC’s. Also, I have recently seen that, by refreshing the browser page, the spikes go away.
You know that competing sensors (of which there are several) all use 10-minute averages for the default plots. This would flatten out spikes and would greatly improve the appearance of the PM graphs. This would be done at the server end of things I suppose.
This summer, the formaldehyde sensor is – for the first time ever – starting to produce some readings. I wonder if you have changed some software? or if my air is dirtier this year than ever before?
The VOC and formaldehyde readings tend to track each other (mirror image) indicating a common gas is being detected. Probably not actually formaldehyde. Both sensors respond to a a variety of gasses.
The unit is fed from a 24 volt supply and POE injector/splitter.
Actual voltage arriving at uRad is about 20 volts when using the 24 volt supply.The center portion of this graph is with the 18-volt battery supply (3×6.3).
The right hand side is back on the 24 volt supply with some added filtering – I can do more.
I can also try lowering the voltage, as I found everything else on the system works at 18 volts.
You can see the readings average about the same values with either supply.I an quite sure the O3 sensor is responding to other compounds in the air. I found it is quite sensitive to alcohol and the forest here emits natural compounds that are chemically similar to alcohol. The second photo shows the month of September. Readings are rarely below 100 ppb and tend to show a peak right after it rains, when soil bacteria naturally emit a compound that the O3 sensor seems to detect quite well.
Ken
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OK – answering my own question. The B unit has a bigger fan than the OEM “A” unit. The attached photo shows the old one on the left and the new one (already connected) on the right.
As it was, the OEM did not fit very well either. It was *very* difficult to get it out of the case.
To get the new one in I decided to cut off piece of the circuit board, remove two of the screws holding the fan on and file down one corner of the PM unit.
The result is shown in the last photo where some white space is left so you can see how it fits. It is quite impossible to mount the PM unit on top of the PCB, as both the -A and B versions are the same height as the enclosures. I have no idea how uRad was able to get the PM unit in there originally.
It has been running for a bit over ah hour now and looks like it will be OK.
Regards
KenWell – my power supply feeds two other units at the same location and they do not have problems (it is a battery-backed supply). As posted elsewhere, what is happening is that the A3 simply stops communicating over the ethernet port – even to local hosts – so nothing to do with my router. That ethernet failure apparently is in both directions so, not hearing anything coming in either, the program reboots. I have my fingers crossed now because it has run up to 410K seconds which is some kind of record for my unit….
But the topic is CO2 calibration. Update there: after about 2 weeks the A3 spontaneously decided it was time to reset the calibration so that the minimum values are about 400 PPM. This did not coincide with a reboot. I have read in another post where someone else’s unit did the something similar. I posted the month of CO2 readings so you can see what it did. The two upward steps were when I adjusted the height of the unit. No other sensor jumps coincided with the reset to 400. It was at 9:22 AM July 26. I will be watching on August 26th to see if anything interesting happens 🙂
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