PASCO PS-2108 Dissolved Oxygen Sensor - Manual (Page 7)

Model No. PS-2108 Dissolved Oxygen Sensor
3 ®
The negatively charged hydroxide ions diffuse to the silver anode. There they combine with
silver (Ag) atoms from the silver anode, forming silver oxide and releasing electrons that join
the current in the electrode in the following chemical reaction:
The released electrons produce a current that passes from the electrode and is amplified. The
current due to the chemical reactions of the O
2
molecules must be corrected for temperature
variations, since the rate of reaction varies directly with the temperature.
The correction is accomplished through the use of a temperature-sensing thermistor that is
built into the probe. With the temperature sensing thermistor, the temperature of the probe is
monitored, and the gain of the amplifier is automatically adjusted to compensate for the
temperature dependence of the chemical reactions in the probe. A signal representing the
temperature-compensated dissolved O
2
concentration of the solution is fed to the computer
interface and displayed by DataStudio in concentration (mg/l) or saturation (%).
DO Sensor Setup and Calibration
Prepare the Sensor for First Use
Prior to the first use of the sensor, you will need to fill the Dissolved Oxygen Sensor electrode
membrane cartridge and cartridge housing with an electrolyte solution. See the maintenance
section for instructions.
Set up the Dissolved Oxygen Sensor with DataStudio.
1. Attach the probe to the sensor box (Figure 3).
2. Plug the sensor box into a PASPort interface or logger connected to a computer.
3. The PASPortal window should open, allowing a choice between DataStudio or EZScreen.
Select DataStudio.
4. The Digits display opens automatically. Open additional or alternate displays as desired.
4Ag 4OH
-
2Ag
2
O 2H
2
O 4e
-
Reduction potential = 0.343V
 
+ +

+
Figure 3
Plug the DO
2
probe into the DO
2
sensor box and connect the sensor box to a PASPort USB interface that is
connected to a computer’s USB port or to a USB hub that is connected to the computer.
1
Find a more detailed discussion in Michael L. Hitchman, Measurement of Dissolved Oxygen, John Wiley and Sons,
New York, 1978, pp. 59-123.