K-O2 Oxygen Sensor
5/20/2022
Kele, Inc. • 3300 Brother Blvd. • Memphis, TN 38133
Page 8
www.kele.com
5
S
ENSOR
C
ALIBRATION
The sensitivity of the galvanic oxygen sensor used on the K-O2 series decreases as the sensor ages. Over the
sensor’s lifetime its accuracy decreases by about 30%. Without intervening calibrations, the sensor will typically
indicate about 14.7 % oxygen concentration in fresh air after 5 (for the K-O2-x5) or 10 (for the K-O2-x10) years.
Required calibration frequency depends on the accuracy requirement of the application. To maintain the accuracy
specified in Table 5 over the full operating range of the K-O2 series, a full calibration interval of 6 months is
recommended. Annual calibration will typically maintain an accuracy within about 0.5% O
2
(for K-O2-x5) and
about 0.3% O
2
(for K-O2-x10).
For best accuracy, the full two-step calibration process that provides the sensor module with oxygen-free ‘zero’
gas, and then a 21% ‘span’ gas is required. Two calibration buttons (
ZERO
and
SPAN
) are provided on the main
board to initiate each calibration operation as shown in Figure 8.
For applications between 18% and 21% oxygen, a span-only calibration is often adequate and requires no
calibration gas. All that’s required is the certainty of fresh air around the sensor. For accuracy at lower oxygen
percentages, a zero calibration before the span calibration is recommended.
To perform a gas-less span calibration
: follow the procedure in section 5.4, ignoring all instructions regarding the
application or removal of calibration gas or fittings.
The ‘sensor expired’ test will be performed at the end of a span calibration.
If the sensor’s sensitivity has fallen
below manufacturer’s end-of-life specification, the K-O2 goes into Sensor Expired mode with the front cover LED
slowly blinking RED, the analog output at a constant 4 mA and the warning/ventilation relay activated. The
oxygen sensor is no longer operational and must be replaced (See section 6).
The status of the calibration process is indicated by the flash pattern of the front cover LED as shown below.
Blinking Green
Successful sampling. Waiting for user to confirm cal
gas removal.
Blinking Red
Failed calibration attempt. Waiting for user to
acknowledge with either a re-try or an exit.
Green/Yellow
During ambient equilibration period after successful
calibration.
New calibration is applied.
Red/Yellow
During ambient equilibration period after failed
sampling.
Old calibration is unchanged.
Table 10:
Meaning of Status LED Blink Patterns During Calibration.