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MODEL SOLU COMP II
SECTION 5.0
PROGRAMMING THE ANALYZER
5.5 SELECTING THE TYPE OF MEASUREMENT
5.5.1 Purpose
This section describes how to do the following:
1.
Program the Solu Comp II to measure dissolved oxygen, pH, ORP, or redox potential.
2.
Identify the type of dissolved oxygen sensor being used.
3.
Make the following settings for dissolved oxygen
a. barometric pressure units for air calibration
b. electronic filtering of sensor current
c. salinity correction.
4.
Make the following settings for pH
a. solution temperature correction
b. analyzer isopotential point.
c. enable or disable glass impedance fault.
5.5.2 Definitions — Dissolved Oxygen
1.
TYPE OF DO SENSOR. The Solu Comp II is compatible with three types of dissolved oxygen sensors avail-
able from Rosemount Analytical: conventional DO sensors used primarily in aeration basins, dissolved oxygen
sensors for the determination of trace (ppb) oxygen in boiler feedwater, and steam-sterilizable sensors for bio-
pharmaceutical manufacturing. The sensors have different temperature elements and membrane permeability
corrections and, in some cases, require different polarizing voltages. By answering a series of questions, the
user tells the analyzer which sensor is being used. The Solu Comp II is also compatible with certain steam-
sterilizable sensors available from other manufacturers. Consult the factory for additional information.
2.
INPUT FILTER. Before converting the sensor current to a dissolved oxygen reading, the Solu Comp II applies
an input filter. The filter reduces noisy readings, but increases the response time. The level of filtering is select-
ed by choosing the amount of time required for the display to reach 63% of a step change.
3.
PRESSURE UNITS. During air calibration, the analyzer uses the barometric pressure to calculate the partial
pressure of oxygen, from which it calculates the equilibrium solubility of atmospheric oxygen in water. The user
can select the units in which barometric pressure is displayed.
4.
SALINITY. The solubility of oxygen in water depends on the concentration of dissolved salts in the water.
Increasing the concentration of electrolytes reduces the solubility of oxygen—the so called salting-out effect.
If the concentration of salts is less than about 1000 ppm, the effect is negligible. When the oxygen sensor is
calibrated, the analyzer assumes that measurements will be made in water containing a relatively low con-
centration of dissolved salts. If the salt concentration is greater than about 1000 ppm, accuracy can be
improved by applying a salinity correction. Enter the salinity as parts per thousand (
o
/
oo
) of sodium chloride. If
the water contains a mixture of electrolytes, enter the ionic strength (as parts per thousand as NaCl). One per-
cent is ten parts per thousand.
5.
PERCENT SATURATION. Percent saturation is the concentration of oxygen in the sample divided by the sat-
uration concentration. The saturation concentration is the maximum amount of oxygen the sample can hold at
a given temperature.
