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IAQ User experience during initial operation

IAQ User experience during initial operation
This whitepaper documents some key considerations when using CCS8xx product family of MOX gassensors for the first time and the potential impact on the Indoor Air Quality (IAQ) end-user
experience in the first few days of operation.
CCS8xx refers to CCS811 and CCS801 with MOX software libraries which include proprietaryalgorithms.

Early-Life Use
CCS8xx performance in terms of resistance levels and sensitivities will change during early life use.
The following chart shows typical early resistance over multiple devices.

Typical Early Life
900,000
800,000

700,000

Ra (ohms)

600,000
500,000
400,000
300,000
200,000
100,000
00246810Days

Typical Early Life change in baseline resistance (Ra)During the early life phase the change in resistance is greatest over the first 24 – 48hrs of operation.
Burn-in is a process to accelerate this phase of the CCS8xx, and thereby minimise changes during
normal user operation.
Cambridge CMOS sensors (CCS) recommends where possible CCS8xx runs in continuously for at least
24hrs to ensure performance is more stable and can be used to provide a more accurate indicationof the IAQ level.

Page | 1© Cambridge CMOS Sensors Ltd, Deanland House, Cowley Road, Cambridge, CB4 0DL, UKWebsite: www.ccmoss.com

Telephone: +44 1223 395 551

Date Issued: 22 Apr 2016

CC-001011-WP revision: 1IAQ User experience during initial operationConditioning Period
The conditioning period is the time required to achieve good sensor stability before measuring VOCs
after power-on. The chart below shows the average of 8 x CCS8xx sensors in DC (1s mode) andPulsed (60s mode). If the CCS8xx sensor has been left in an idle condition for 8 hours or more, thenCCS recommends running the CCS8xx initially for >20 minutes before measuring the IAQ level. Thisapplies to all IAQ modes supported by CCS8xx.

CCS8xx Sensor Conditioning Period

CCS8xx could be used with much shorter conditioning period, but this will result in inaccurate IAQ
readings until the sensor is warmed up.

Environmental Changes
TVOC and eCO2 readings generated by CCS8xx while monitoring VOCs will be impacted by humidity
and temperature changes. CCS recommends that an external temperature + humidity sensor isincluded in the system design.
This information can be written to CCS8xx by the host system and used to compensate fortemperature and humidity changes.

24hr Automatic Baseline Correction
The CCS8xx continuously monitors the baseline that is used to calculate the TVOC and eCO2
concentrations in all modes of operation. The VOC concentration levels will vary in typical indoor
environments so the recommended minimum time over which an automatic baseline correction isimplemented is 24 hours. CCS8xx automatically tracks the lowest level over a 24hr period.
Corrections are expected to be small but may occasionally be observed.
Page | 2© Cambridge CMOS Sensors Ltd, Deanland House, Cowley Road, Cambridge, CB4 0DL, UKWebsite: www.ccmoss.com

Telephone: +44 1223 395 551

Date Issued: 22 Apr 2016

CC-001011-WP revision: 1

IAQ User experience during initial operation
IAQ monitoring in a Polluted Environment
CCS8xx only detects relative changes to gas concentrations. This means the sensor will initiallycalculate the gas concentration for the ambient air treating this as clean air. This will automaticallychange when the sensor is exposed to clean air. Then if the air quality deteriorates this will produce
a more accurate IAQ reading.
To avoid accuracy issues during start-up when operating in a polluted environment for a long period,
CCS8xx supports saving and restoring of the baseline. A clean air baseline for this particular sensor
needs to be saved by the application when clean air has been encountered after the conditioning
period and not during early life. The CCS8xx has no way of retaining the baseline value in nonvolatile memory (NVM) so this needs to be saved by the host system and restored to the CCS8xx
register periodically.
The clean air baseline is considered to be unique for each sensor and is not constant, therefore willchange over the time as the sensor ages. CCS recommends that the baseline is saved periodically by
the application every 24 hours. This allows the most accurate baseline to be written to the CCS8xx
the next time the sensor is powered on.

End-User experience
CCS8xx will detect low level of VOCs typically found in indoor environments and CCS software
libraries with proprietary algorithms and example applications are available to represent themeasured values as an equivalent CO2 level.
The following table illustrates the effects of poor indoor air quality, and default levels set for good,moderate and poor indoor air quality indicators in CCS8xx.
Air Quality
Indication

POOR

VOC LevelHigh

CO2 Level

Effects of poor Indoor Air Quality> 2500 ppm

Long Term Exposure: Carcinogenic, Lungs, Liver,
Kidney & Central Nervous System damage
Eye, Nose, Throat, Skin Irritation, Headaches,Nausea, Dizziness
Significant Impairment of Performance &Decision-Making.
Eye, Nose, Throat, Skin Irritation, Headaches,Nausea, Dizziness

MODERATE

Medium

1500 – 2500 ppm
Moderate Decision-Making Fatigue, Impairmentand Concentration.

GOODLow< 1500 ppm

No impact on health or decision making

Effects of poor Indoor Air Quality

Page | 3© Cambridge CMOS Sensors Ltd, Deanland House, Cowley Road, Cambridge, CB4 0DL, UK

Website: www.ccmoss.com

Telephone: +44 1223 395 551

Date Issued: 22 Apr 2016

CC-001011-WP revision: 1

IAQ User experience during initial operation
These levels indicate issues with poor indoor air quality in your local environment and alert the enduser to take appropriate action. During early life use CCS8xx performance in terms of resistancelevels and sensitivities will change therefore the initial IAQ indication may not be accurate. CCS
recommends in the first 24hrs of operation the end-user treats any IAQ indication with caution orignores them.

Summary
To avoid IAQ inaccurate readings in first few days of operation CCS recommends the following:Due to early life behaviour the sensor should be powered-on and run in continuous
operation for at least 24hrs to avoid inaccurate IAQ readings

A conditioning (warm-up) period of >20mins if sensor have been idle for more than 8hrs



An external temperature + humidity sensor is fitted to provide feedback to CCS8xx tocompensate for environmental changes

A new baseline value is saved periodically by the application every 24 hours

In the first 24hrs of operation the end-user should treat any IAQ indication with caution orignore them.

Page | 4© Cambridge CMOS Sensors Ltd, Deanland House, Cowley Road, Cambridge, CB4 0DL, UKWebsite: www.ccmoss.com

Telephone: +44 1223 395 551

Date Issued: 22 Apr 2016