Development of the U-50 Series Multi-parameter Water Quality ...

dissolved oxygen (DO), pH, conductivity, ORP,water depth, and temperature is embedded into10-cm diameter probe base. The sensors forturbidity, DO, pH, and ORP are removable andeasy to replace.Membrane Cap3. Comparison of the U-20 and U-50Table 1 compares the specifications of the U-20and newly developed U-50 series. As shown in thetable, improvements were also made to eachmeasurement parameter. Significantimprovements were made particularly in theturbidity meter and dissolved oxygen electrode.The turbidity meter in the U-20 uses an LED asthe light source with a 30 degree scatteringmethod. Meanwhile, the U-50 series model U-53uses a tungsten lamp as the light source with a 90degree scattering method. This method complieswith the US EPA Method 180.1, and is strongagainst chromaticity differences while beinghighly sensitive to small particles. Prior to themeasurement, the wiper can clean the sensorwindow to reduce the influences of air bubblesand dirt.The dissolved oxygen sensor on the U-50 is basedon the polarographic method, whereas on theU-20 the galvanic battery system. This means theelectrode can be lead-free, making it exempt ofrestrictions imposed by the European RoHSregulation. As shown in Figure 3, the oxygenisolation film is shaped like a cap. This allows thecustomer to replace the film simply by tighteningthe film cap. Additionally, the measurementrange was expanded.Table 2 shows potential new measuringapplications for the U-50 series afforded by theseimprovements. The improved turbiditymeasuring accuracy enables measurement andcontrol of ground water, environmental water,and plant water with low turbidity. Turbiditysensors in previous multi-parameter waterquality checkers are not capable of measuring lowturbidity concentrations. Users who accustomedto measuring turbidity separately will appreciatethe simplified and simultaneous measurement.The expanded measuring range for dissolvedoxygen enables measurement and control of highconcentrations of oxygenated water such asoxygen enriched drinking-water and thephotosynthetically-activated environment water.The expanded measuring range for conductivityenables measurement of high salinity samplessuch as seasonings solution in the food makingindustry.DO Sensor Main BodyFig.3 Structure of DO Sensor4. Measurement ExamplesThe changes in turbidity and dissolved oxygen asmeasured continuously over 12 days in Inba-pond,Chiba prefecture is shown in Figure 4. When webegan measuring on May 28, the turbidity was20.5 NTU and the COD value was 10.0 ppm. Theturbidity and COD value dropped during themeasurement period and became 5.89 NTU and8.8 ppm, respectively, on the last day of June 9.This result suggests decrease in organic matter.The dissolved oxygen (DO) concentrationincreased from the morning to the afternoon, anddecreased from the evening to the followingmorning. This is the result of oxygen generated byphotosynthesis in the afternoon, and oxygenconsumed by breathing during thenight.Although traces of organic matter werefound on the measurement unit after 12 days ofcontinuous measurement, the wiper kept the cellwindow on the turbidity meter in a clean state.