YSI 600DW-B, Руководство пользователя

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Principles of Operation Section 5
YSI Incorporated Drinking Water Monitoring Systems Operation Manual 5-5
59). Determination of the slope of pH vs. mv plots at temperatures different from T
c
is thus relatively
simple. In order to establish the intercept of the new plot, the point where plots of pH vs. mv at different
temperatures intersect (the isopotential point) must be known. Using standard pH determination protocol,
the sonde software assigns the isopotential point as the mv reading at pH 7 and then calculates the intercept
using this assumption. Once the slope and intercept to the plot of pH vs. mv are assigned at the new
temperature, the calculation of pH under the new temperature conditions is straightforward, and is
automatically carried out by the sonde software.
MEASUREMENT AND CALIBRATION PRECAUTIONS
1- When filling the calibration cup prior to performing the calibration procedure, make certain that the level
of calibrant buffers is high enough in the calibration/storage cup to cover at least ½ inch of the pH probe
and the temperature sensor of the 6560 probe.
2 - Rinse the sensors with deionized water between changes of calibration buffer solutions.
3 - During pH calibration, allow the sensors time to stabilize with regard to temperature (approximately 60
seconds) before proceeding with the calibration protocol. The pH readings after calibration are only as
good as the calibration itself.
4 - Clean and store the probe according to the instructions found in
Section 2.10, Care, Maintenance and
Storage of this manual.
5.6 5.6 5.6 5.6 TEMPERATURE TEMPERATURE TEMPERATURE TEMPERATURE
The sondes utilize a thermistor of sintered metallic oxide that changes predictably in resistance with
temperature variation. The algorithm for conversion of resistance to temperature is built into the sonde
software, and accurate temperature readings in degrees Celsius, Kelvin, or Fahrenheit are provided
automatically. No calibration or maintenance of the temperature sensor is required.
5.7 5.7 5.7 5.7 FREE CHLORINE FREE CHLORINE FREE CHLORINE FREE CHLORINE
CHLORINE CHEMISTRY
When chlorine gas (Cl
2
) is added to water, a reaction (called disproportionation) occurs to form hypochlorous acid
(HOCl) and hydrochloric acid (HCl). The hypochlorous acid is a strong oxidant and the active species in most drinking
water disinfection processes rather than gaseous chlorine (Cl
2
). One molecule of HOCl has the same oxidizing
capacity as a molecule of Cl
2
. Thus, the formula for “free chlorine” is really HOCl rather than Cl
2
. (Depending on the
pH of the sample some of the HOCl may also be in the form of hypochlorite ion OCl
-
). However, convention dictates
that free chorine be reported in units of “mg Cl
2
per liter” even though the active compounds in solution are HOCl and
OCl
-
. Thus, YSI free chlorine readings are expressed in units of “Cl2 mg/L” rather than “HOCl/OCl
-
mg/L” to be
consistent with standard reporting convention.
There are two categories of “chlorine” in most treated drinking water – free chlorine (HOCl + OCl
-
) and combined
chlorine which is made up of species formed in the reaction of free chlorine with ammonia which is present in the
water. Combined Chlorine is thus made up of a general class of compounds called chloramines with formulae such
as NH
2
Cl, NHCl
2
, and NCl
3
. In water which is treated just with chlorine, there will be a small amount of combined
chlorine from the natural ammonia in the water and a large amount of free chlorine; in water which is treated with both
free chlorine and ammonia there will be a small amount of free chlorine and a large amount of combined chlorine.
Total Chlorine is defined as the sum of the free and combined chlorine concentrations . Combined chlorine is