TD 269 OPERATING MANUAL
OXYGEN OPTODE 4330, 4831, 4835
June 2017
page 17 of 93
All the user configurable properties that can be changed for each individual sensor, i.e. calibration
coefficients, are called sensor properties. The properties can be displayed and changed using the Smart
Sensor Terminal protocol via an RS232 port, refer CHAPTER 5 for communication with the sensor using
a terminal communication program. Examples of typical terminal emulation programs are Hyper Terminal
and Tera Term
The Oxygen Optode will perform a measurement sample and present the result within the first 1.5
seconds after the Optode has been powered up.
2.2 Sensor Parameters
Engineering data are calculated by firmware in the sensor based on measured raw data and sets of
calibration coefficients stored in the sensor:
•
The Oxygen content is presented in
µ
M (1 Molar = 1 mole/litre). Conversions to other commonly used
engineering unit values are:
o
1 ml/l = 44.66 µM, (real gas STP)
o
1 mg/l = 31.25 µM.
Please observe that to obtain absolute concentrations of oxygen these values needs to be
salinity and pressure compensated (see below).
•
The relative Air Saturation is presented in % relative to the nominal air pressure (1013.25 hPa).
These values do not need to be salinity compensated.
•
The ambient Temperature is presented in ºC.
The optode raw data are the phase and amplitude of the returned signal after the luminophore quenching:
CalPhase(deg):
Calibrated phase
TCPhase(deg):
Temperature compensated phase
C1RPh(deg):
Phase measurement with blue excitation light
C2RPh(deg):
Phase measurement with red excitation light
C1Amp(mV):
Amplitude measurement with blue excitation light
C2Amp(mV):
Amplitude measurement with red excitation light
RawTemp(mV):
Voltage from thermistor bridge.
The 4831 analog channel 1 may be set to output either; µM or %Saturation or CalPhase.
Calibration coefficients are stored in the sensors flash and are updated when recalibrated. If raw data are
not needed the user can select to turn off the delivery and logging of these.
2.3 Salinity Compensation of Data
The O
2
concentration sensed by the Optode is the partial pressure of dissolved oxygen in water.
Since the foil is only permeable to gas and not water, the optode cannot sense the effect of salt dissolved
in the water, hence the optode always measures as if immersed in fresh water.
If the salinity variation on site is minor (less than
±
1ppt), the O
2
concentration can be compensated in
real-time inside the sensor by setting the internal property ‘
Salinity’
to the average salinity at the
measuring site.
