Water Analytics AquaMetrix AM-2250 Installation And Operation Manual
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302250-series Operating Manual rev 2.05.3.1 About Conductivity CalibrationAs with ORP calibration there are no recognized standard calibration standards so there is no autocalibration option. Also, as with ORP, conductivity calibration standards are not buffered and can change.Stability of the conductivity standard is only a problem for standards of very low conductivity, whereintroduction of impurities in the solution can induce large changes in conductivity. At conductivitystandards below 5 μS/cm just carbon dioxide in the air can increase the actual conductivity.In those cases where a conductivity standard is not available one may enter the cell constant of the probeas an approximate surrogate to calibration. Obviously, the calibration using the known cell constant isonly as good as the cell constant is known. Usage of the probe will cause some scaling or fouling of theelectrodes, which will result in an increased nominal cell constant. Therefore, calibration using real a realconductivity standard is always preferred.Most conductivity analyzers employ a calibration routine that uses only one calibration standard. This isactually a two-point calibration routine inasmuch as the other point is assumed to be zero, i.e. that theconductivity for a zero-conductivity sample is zero. The AM-2250 allows as many as 16 points. Thoughone point is sufficient for most applications the ability to calibrate over several points allows one to useconductivity measurements to determine acid and base concentrations. As the figure below showsconductivity as a function of acid/base concentration is very non-linear and, therefore, several points areneeded to construct the curved relationship. Therefore, multi-point calibration also enables greateraccuracy over a wider range of conductivities.Figure 5-1 Relationship between Concentration of solution and conductivity (at 25° C)5.3.2 Manual Conductivity Calibration or Wet CalibrationThe procedure for manual conductivity calibration is similar to that for manual pH and ORP calibration.The only exception is that user can calibrate using as many as 16 points.1. Select Manual Calibration.2. Select the number of calibration standards to be used. In most cases choose 1. For greateraccuracy choose 2 or 3. Only for measuring acid and base concentrations or conductivities over awide range are more points needed. Press Enter to accept the number of points.0100,000200,000300,000400,000500,000600,000700,000800,000900,0001,000,0000 10 20 30 40 50 60 70 80 90 100Conductivity, μS/cmConcentration, %NaCINaOHHCIH2SO4HNO3HF |
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