documents/PurpleAir_CF=ATM_vs_CF=1.md
In MazamaScience/AirSensor: Process and Display Data from Air Quality Sensors
This is a verbatim copy of the similarly named .pdf file in this directory.
This document was a personal communication on May 8, 2020 and is reproduced here
as a .md file for easy reading.
PurpleAir CF=ATM vs CF=1
This document describes the meaning and labeling of CF=ATM and CF=1 fields in
the PurpleAir sensors. It will discuss a bug that caused the labels for these
two sets of particulate readings to be swapped and what PurpleAir has done about
that.
Background
Plantower laser counters used in the PurpleAir sensors output two sets of
particulate measurements with different “correction factors”. These correction
factors were developed by the manufacturer, Plantower, and the methodology of
the development of these correction factors is unknown. While there are unknowns,
the manufacturer has provided direction in the operational manual for the PMS5003,
stating that the CF=1 is applicable for a standard environment (indoors / chamber)
while the CF=ATM is applicable under atmospheric environment (outdoors / am202bient).
The PMS5003 operational manual can be accessed here:
http://www.aqmd.gov/docs/default-source/aq-spec/resources-page/plantower-pms5003-manual_v2-3.pdf?sfvrsn=2
History
When PurpleAir started, we had no detailed manual for the PMS laser counters and
as such no clear understanding of the meaning of, or the differences between these
two sets of data.
We knew that the one set read lower at higher concentrations and since the sensors
were already known to read high, these numbers were chosen to be used to display
on the map.
What Happened?
PurpleAir mistakenly labeled the lower readings CF=1 and the higher set of
numbers CF=ATM. All three readings for PM1, PM2.5 and PM10 were swapped. This
bug was present from day one and did not change during the firmware updates all
the way up to version 4.11.
How we are fixing it
ThingSpeak Data
On October 20th 2019, PurpleAir updated the download tool
(www.purpleair.com/sensorlist), fixing the labels so any files downloaded after
that date will have the correct column headers. There will not be any changes to
thingspeak data fields uploaded by the PurpleAir firmware. All past downloaded
data is still valid if you use the new column headers.
JSON data
Firmware version 5.0 will be an update that corrects the labels in the json
produced by the sensor and uploaded to PurpleAir servers as well as third party
providers such as custom servers and Azure. JSON data uploaded to Weather
Underground does not change.
SD Card Data
In firmware V5.00, the same data is written to the same columns. The only change
is in the CSV headers which are updated with the correct labels. All past data
is still valid assuming you use the new headers.
PurpleAir Map
The PurpleAir map has always used the lower of the two numbers (CF=ATM). PurpleAir
updated the map on 21 November 2019 to selectively use CF=ATM or CF=1 values for
outdoor and indoor sensors respectively. The PurpleAir map will interpret the
older firmware’s messages correctly, swapping the fields as needed.
Summary of changes
- Thingspeak: The fields uploaded to thingspeak do not change in that the same
data is uploaded to the same fields after version 5 firmware. The labels in the
download tool (www.purpleair.com/sensorlist) were corrected on the 20th October
2019.
- SD Data: Column order does not change. The same data is written to the same
columns. Only the headers were updated to swap CF=ATM and CF=1 labels.
- Custom data providers using JSON: CF=ATM and CF=1 labels will be swapped in f
irmware V5.00 and up. All firmware prior to V5.00 will have the CF=ATM and CF=1
labels swapped in any JSON.
- Weather Underground data is not affected and always had CF=ATM data uploaded
to the service.
How to determine what data is what
Since CF=ATM values only differ from CF=1 values at higher concentrations, you
will not see any difference between the values till the concentrations reach
around 50ug/m3. The CF=ATM values will always be the lower of the two, so it
would be safe to assume that if one field is lower in value, that field is the
CF=ATM value.
Summary:
| Plantower PMS Sensor Bytes Data | PA JSON <= 4.11 | PA JSON >= 5.0 | Thingspeak | Weather Underground
---- | ---- | ---- | ---- | ---- | ----
4,5 | PM1.0 CF=1 | pm1_0_atm | pm1_0_cf_1 | field1 - primary data |
6,7 | PM2.5 CF=1 | pm2_5_atm | pm2_5_cf_1 | field2 - primary data |
8,9 | PM10 CF=1 | pm10_0_atm | pm10_0_cf_1 | field3 - primary data |
10,11 | PM1.0 CF=ATM | pm1_0_cf_1 | pm1_0_atm | field7 - secondary data | Uploaded as PM1.0
12,13 | PM2.5 CF=ATM | pm2_5_cf_1 | pm2_5_atm | field8 - primary data | Uploaded as PM2.5
14,15 | PM10 CF=ATM | pm10_0_cf_1 | pm10_0_atm | field8 - secondary data | Uploaded as PM10
Questions? Contacting PurpleAir
We hope this document helped to explain the differences and labeling of CF=ATM
and CF=1 values.
If you have any questions or concerns about this or other topics, please contact
PurpleAir by email at contact@purpleair.com, by phone on 1-800-474-0696 or on
our web site at www.purpleair.com/contact.
MazamaScience/AirSensor documentation built on April 28, 2023, 11:16 a.m.
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This is a verbatim copy of the similarly named .pdf file in this directory.
This document was a personal communication on May 8, 2020 and is reproduced here
as a .md file for easy reading.
PurpleAir CF=ATM vs CF=1
This document describes the meaning and labeling of CF=ATM and CF=1 fields in the PurpleAir sensors. It will discuss a bug that caused the labels for these two sets of particulate readings to be swapped and what PurpleAir has done about that.
Background
Plantower laser counters used in the PurpleAir sensors output two sets of particulate measurements with different “correction factors”. These correction factors were developed by the manufacturer, Plantower, and the methodology of the development of these correction factors is unknown. While there are unknowns, the manufacturer has provided direction in the operational manual for the PMS5003, stating that the CF=1 is applicable for a standard environment (indoors / chamber) while the CF=ATM is applicable under atmospheric environment (outdoors / am202bient).
The PMS5003 operational manual can be accessed here: http://www.aqmd.gov/docs/default-source/aq-spec/resources-page/plantower-pms5003-manual_v2-3.pdf?sfvrsn=2
History
When PurpleAir started, we had no detailed manual for the PMS laser counters and as such no clear understanding of the meaning of, or the differences between these two sets of data.
We knew that the one set read lower at higher concentrations and since the sensors were already known to read high, these numbers were chosen to be used to display on the map.
What Happened?
PurpleAir mistakenly labeled the lower readings CF=1 and the higher set of numbers CF=ATM. All three readings for PM1, PM2.5 and PM10 were swapped. This bug was present from day one and did not change during the firmware updates all the way up to version 4.11.
How we are fixing it
ThingSpeak Data
On October 20th 2019, PurpleAir updated the download tool (www.purpleair.com/sensorlist), fixing the labels so any files downloaded after that date will have the correct column headers. There will not be any changes to thingspeak data fields uploaded by the PurpleAir firmware. All past downloaded data is still valid if you use the new column headers.
JSON data
Firmware version 5.0 will be an update that corrects the labels in the json produced by the sensor and uploaded to PurpleAir servers as well as third party providers such as custom servers and Azure. JSON data uploaded to Weather Underground does not change.
SD Card Data
In firmware V5.00, the same data is written to the same columns. The only change is in the CSV headers which are updated with the correct labels. All past data is still valid assuming you use the new headers.
PurpleAir Map
The PurpleAir map has always used the lower of the two numbers (CF=ATM). PurpleAir updated the map on 21 November 2019 to selectively use CF=ATM or CF=1 values for outdoor and indoor sensors respectively. The PurpleAir map will interpret the older firmware’s messages correctly, swapping the fields as needed.
Summary of changes
- Thingspeak: The fields uploaded to thingspeak do not change in that the same data is uploaded to the same fields after version 5 firmware. The labels in the download tool (www.purpleair.com/sensorlist) were corrected on the 20th October 2019.
- SD Data: Column order does not change. The same data is written to the same columns. Only the headers were updated to swap CF=ATM and CF=1 labels.
- Custom data providers using JSON: CF=ATM and CF=1 labels will be swapped in f irmware V5.00 and up. All firmware prior to V5.00 will have the CF=ATM and CF=1 labels swapped in any JSON.
- Weather Underground data is not affected and always had CF=ATM data uploaded to the service. How to determine what data is what Since CF=ATM values only differ from CF=1 values at higher concentrations, you will not see any difference between the values till the concentrations reach around 50ug/m3. The CF=ATM values will always be the lower of the two, so it would be safe to assume that if one field is lower in value, that field is the CF=ATM value.
Summary:
| Plantower PMS Sensor Bytes Data | PA JSON <= 4.11 | PA JSON >= 5.0 | Thingspeak | Weather Underground ---- | ---- | ---- | ---- | ---- | ---- 4,5 | PM1.0 CF=1 | pm1_0_atm | pm1_0_cf_1 | field1 - primary data | 6,7 | PM2.5 CF=1 | pm2_5_atm | pm2_5_cf_1 | field2 - primary data | 8,9 | PM10 CF=1 | pm10_0_atm | pm10_0_cf_1 | field3 - primary data | 10,11 | PM1.0 CF=ATM | pm1_0_cf_1 | pm1_0_atm | field7 - secondary data | Uploaded as PM1.0 12,13 | PM2.5 CF=ATM | pm2_5_cf_1 | pm2_5_atm | field8 - primary data | Uploaded as PM2.5 14,15 | PM10 CF=ATM | pm10_0_cf_1 | pm10_0_atm | field8 - secondary data | Uploaded as PM10
Questions? Contacting PurpleAir
We hope this document helped to explain the differences and labeling of CF=ATM and CF=1 values.
If you have any questions or concerns about this or other topics, please contact PurpleAir by email at contact@purpleair.com, by phone on 1-800-474-0696 or on our web site at www.purpleair.com/contact.
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