YSI 3200 Operation Manual

Contents

YSI 3200 Operation Manual Manual pdf 54 page image

Principles of Operation Section 88.3 SALINITYSalinity is determined automatically from the Model 3200 conductivity and temperature readingsaccording to algorithms found in Standard Methods for the Examination of Water andWastewater (ed. 1995). The use of the Practical Salinity Scale 1978 results in values which areunitless, since the measurements are carried out in reference to the conductivity of standardseawater at 15°C. However, the unitless salinity values are very close to those determined by thepreviously-used method where the mass of dissolved salts in a given mass of water (parts perthousand) was reported. Hence, the designation "ppt" is reported by the instrument to provide amore conventional output.8.4 TOTAL DISSOLVED SOLIDSTotal dissolved solids (TDS) is determined automatically by the Model 3200 by multiplyingconductivity by an empirical factor (Standard Methods for the Examination of Water andWastewater ed. 1995). The factor may vary from 0.55 to 0.9, depending on the composition of thewater and the temperature.8.5 TEMPERATUREThe Model 3200 system utilizes a thermistor of sintered metallic oxide that changes predictablyin resistance with temperature variation. The algorithm for conversion of resistance totemperature is built-in to the Model 3200 software, and accurate temperature readings in degreesCelsius or Fahrenheit are provided automatically. No calibration or maintenance of thetemperature sensor is required.8.6 SOURCES OF ERRORSCELL CONTAMINATIONThis error is usually due to contamination of the cell by some previous solution. Normally this isin the form of an organic film that reduces the solution-electrode interface conductance. Followthe cleaning instructions carefully.An entirely different form of contamination sometimes occurs when cells are stored for longperiods of time wet; alga and other life forms grow on the electrodes. While rare, such depositshave, on occasion, markedly reduced the effectiveness of the cell by reducing the solution-electrode interface conductance.CELL PLATINIZINGCells that have begun to lose their electrode coating of platinum black when measuring solutionshaving high conductivity values can introduce errors. The effect of poor platinization is a loss oflinearity and a noticeably large change in conductance from range to range on the instrument.When you suspect a problem with the cell platinization, follow the instructions for electrodeinspection and replatinization carefully before attempting any critical measurements.YSI Incorporated Model 3200 50