73
Calibration
U
SER
G
UIDE
CARBON
DIOXIDE SENSOR OPTION (-CO2)
SMART-S
ENSOR
™
2004 – 2014 Reliable Controls
®
Corporation. All rights reserved.
F
IGURE
69: A
UTOMATIC
CALIBRATION
ONCE
EVERY
TWO
WEEKS
If the lowest CO
2
value recorded is 600 PPM, as shown in Figure 69, the sensor will be
automatically calibrated down by 200 ppm (600 - 400). In other words, the calibration will
offset all readings by minus 200.
In the above example, the lowest CO
2
value recorded by the sensor during the two-week
period was 600 ppm, resulting the sensor being automatically calibrated downwards by
200 ppm. If the lowest value recorded actually was 600 PPM, the sensor would be out of
calibration by 200 ppm following execution of the automatic calibration algorithm. For
applications such as continuously occupied rooms, or in densely populated cities, manual
calibration will be required.
M
ANUAL
Manual calibration should be performed on the CO
2
sensor whenever the lowest CO
2
reading in the building does not drop to about 400 PPM at least once every two weeks.
The sensor must be exposed to fresh air at least once every two weeks for the automatic
calibration algorithm to provide an accurate calibration. It doesn't matter when the fresh air
will be sensed, just that it will be sensed at some point during the period.
CO
2
Concen
tratio
n
(PPM
)
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
< Two Weeks >
