DOMeasurement Principle and Devices

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DO-Measurement Principle and Devices
Dr. Edgar Ballin
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DO-Measurement
Principles Toedt Electrodes (without membranes,
reference potential depending on the chloride
concentration of the sample) Clark
Electrodes(large membranes, small membranes,
silicone, Teflon, guard technique)
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DO-Measurement
One Solution
Analyser / Transmitter Stratos 2211 X OXY
WG21A7, Option 470
Sensor / Cable SE 707/1 / ZU 0313
Fitting ARF200 / ZU 0547
safe area
ZU0547
Power supply
4...20 mA
0 / 4...20 mA
Sensor SE 707/1
ARF200
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DO-Measurement
Stratos 2211 X OXY
Special Feature high resolution of the
measurement value 0.01 mg/l resp. 0.01 ppm or
1 µg/l resp. 1 ppb
That resolution differs from the possibilities
with Stratos 2402OXY
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DO-Measurement The Probe
The Probe
Electrolyte
Reference and Anode
Membrane
Cathode
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DO-Measurement The Principle
Reactions in the Oxygen-Electrode
Cathode
Anode
/x4
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DO-Measurement The Principle
NHE
Anode
Cathode
Reduction of Oxygen
Reference System
-
-
-
-
O
2 H
O 4e
4 OH
4 Ag 4 Cl
4 AgCl 4e
2
2
207 mV
-468 mV
Polarization Voltage 675 mV
sesor Current
-800
-600
-400
-200
0
200
400
Voltage / mV
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DO-Measurement The Principle
pO2
pO2
While equilibrium between vapor saturated air and
oxygen saturated water, the partial pressures of
Oxygen are the same!
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DO-Measurement The Principle
Solubility of Oxygen in Water
100 Saturation
8.244
80 Saturation
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DO-Measurement The Principle
Partial Pressure
d pO2 d I
I0
S pO2 I
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DO-Measurement The Principle
Saturation
SI

mg/L
Concentration
c
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DO-Measurement The Calibration
Measurement of Saturation Index
Conditions sensor can be removed for calibration
Aim monitoring and/or controlling of DO addition
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DO-Measurement The Calibration
Measurement of Saturation Index
Configuration (for Stratos) conf 1200
out 1 SAT cal
SAT
Calibration cal 1100
change the presetting for humidity from 100
rel. to 50
START the calibration at the air with ENTER
Install the probe and start the measurement
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DO-Measurement The Calibration
air with rH 50
air with rH 50
measurement mode
100.0
101.5
calibration mode
measurement mode
Oxygen saturated water
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DO-Measurement The Calibration
Components of the Air (at standard air
pressure)partial pressure in mbar or hPa
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DO-Measurement The Calibration
Measurement of Concentration
Conditions sensor can be removed for calibration
Aim monitoring and/or controlling of DO
concentration in mg/l or ppm
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DO-Measurement The Calibration
Measurement of Concentration
Configuration conf 1200 out 1
mg/l or ppm cal
SAT
Calibration cal 1100
presetting humidity 50rel. (can be adjusted)
presetting air pressure 1.013 bar

Remove the sensor and perform the calibration
START the calibration with ENTER(after the
calibration, you will get about 101.6, if the
sensor is still in the air. With the replaced
sensor he value will be correct)
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DO-Measurement
T C 25 25 50 25 25 p mbar 1013 2000 1013 1013
1013 Sal g/kg 0 0 0 20 0 pH2O
mbar 32 32 123 32 32 pO2 mbar 206 412 186 206
161 I nA 60 120 54 60 47 Concentration
mg/l 8.244 16.488 5.030 7.402 6.444 Saturation
Index 100 100 100 100 78.2
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DO-Measurement