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OdaLog® L2 – Gas Logger User Manual
7.
SENSOR OPERATION
The OdaLog® uses an electrochemical sensor to detect levels of a specific gas in ppm (parts per million).
The sensor consists of electrolytes and electrodes packaged in a small container with a diffusion barrier
that the gas passes through.
A subsequent chemical reaction causes current flow within the sensor to change in relation to the level of
gas passing through the diffusion barrier.
This current output is then interpreted within the OdaLog®, displayed on the LCD (in ppm), and recorded
in the OdaLog's data-logging chip.
While the sensors are designed to react to their specific gas type, other gases will also cause chemical
reactions within the sensor, and some of these are listed in (see Section 7.1).
7.1. Sensor Cross-Sensitivity
The presence of other gases can affect the readings of the electrochemical OdaLog® sensors. The chart
below shows how the sensors listed will likely respond to 100 ppm of interfering gases. There may be gases
not on this chart, which also interfere with OdaLog® sensors.
Table V: Cross Sensitivity of H
®
OdaLog
Sensors
H
S
CO
2
H
S
100
<2
2
7.2. Effects of Environmental Changes on OdaLog® Sensors
7.2.1. Temperature
The operating temperature range of OdaLog® sensors is -10°C to +40°C (14oF to 104oF), and within this
range, the sensors are temperature compensated, although extreme temperature swings may cause
sensor drift until the temperature sensor stabilises.
Due to the temperature sensor being located within the OdaLog® body, there is a stabilisation time of up
to an hour when significant temperature changes occur.
7.2.2. Humidity
The sensors fitted to the OdaLog® Logger can be used continuously in atmospheres of 20% to 80% relative
humidity (RH) and can be used intermittently between 0 to 20% and 80 to 99% RH. If used for extended
periods of time at low humidity, the sensor may dry out. Conversely, it may take up water and leak acid at
high humidity.
The Sensor fitted to the OdaLog Instrument is susceptible to reduced response in continuous high-
humidity environments. With the wastewater industry being a common application for the OdaLog, it
is IMPORTANT that users understand the effect humidity has on the sensor, in that it cannot operate
continuously in a „wet‟ (above 80% RH) environment without an ongoing operating and service plan
to ensure the accuracy of logged data.
P/N: 10-1000
S Sensor
2
Approximate response to Interfering Gas at 100 ppm unless noted
SO
NO
NO
2
2
<20
<6
-20
IMPORTANT NOTE ON HUMIDITY
Revision G, January 2024
HCN
HCL
NH
3
0
0
0
H
C
H
O
CH
2
2
4
4
- 20
<1
0
Page | 18
CO
2
0
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