YSI Professional Plus, Калибровочные советы, Страница: 13 / 28

Dissolved Oxygen
The dissolved oxygen sensor should be calibrated every day the instrument is used. It is not necessary to
calibrate in both % and mg/L or ppm. Calibrating in % will simultaneously calibrate mg/L and ppm and vice versa.
CALIBRATION TIPS
1. The Pro Plus can be calibrated in air-saturated water, water-saturated air or against a Winkler Titration. You
can perform a 1 or 2 point DO calibration. A 2 point calibration includes 1 point in a zero oxygen environment
and the 2
nd
point at full saturation.
2. For both ease of use and accuracy, YSI recommends that you perform a 1 point calibration in water-
saturated air.
3. Make sure that there is a good membrane with fresh electrolyte (O2 probe solution) installed on the DO
sensor. The membrane should be clean and free of wrinkles. There should not be any air bubbles present
under the membrane. Membranes should be changed regularly and generally last 2-8 weeks depending on
use and storage.
4. To perform a 1 point calibration in water-saturated air, place the sensor in a 100% humid environment. This
can be accomplished several ways:
a. For the 60520 and 6052030 cables, moisten the sponge in the gray calibration sleeve with a small
amount of clean water and place it over the sensor guard.
b. For the 6051020 and Quatro cables, place a small amount of water in the calibration/storage cup and
place it over the sensors. When screwing the calibration cup onto the sensor bulkhead, only engage
one or two threads. Do not screw the calibration cup completely onto the sensor bulkhead. The goal
is to have air exchange between inside and outside the calibration cup.
The sponge and calibration sleeve/cup should be clean since bacterial growth may consume oxygen and
interfere with the calibration. Be sure the sensor is in air, not water, and that there are not any water droplets
on the membrane or temperature sensor.
5. After entering the % calibration mode, wait approximately 5 to 15 minutes for the storage container to
become completely saturated and, if using a polarographic sensor, to allow the sensor to stabilize.
6. Salinity affects the ability of water to hold oxygen and is used by the instrument to calculate DO mg/L (ppm).
The Salinity value displayed near the top of the DO calibration screen is either the salinity correction value
entered in the Sensor menu or the Salinity value as measured by the conductivity sensor in use. If you are
using a conductivity sensor, ensure that it is calibrated and reading correctly in order to obtain accurate DO
mg/L (ppm) measurements. If you are not using a conductivity sensor, the Salinity correction value should be
the salinity of the water you will be testing. Highlight Salinity and press enter to modify this setting if
necessary. The salinity of fresh water is typically 0-0.5 ppt and seawater is typically 35 ppt.
7. After accepting the calibration, navigate to the GLP menu and record the DO sensor’s value (sensor current
in uA). The acceptable sensor currents when calibration is performed at 25°C, in a 100% saturated air
environment at 760 mmHg are:
1.25 mil PE membrane (yellow membrane): Average 6.15 uA (min. 4.31 uA, max. 8.00 uA)
2.0 mil PE membrane (blue membrane): Average 3.38 uA (min. 2.37 uA, max. 4.40 uA)
1 mil Teflon membrane: Average 16.29 uA (min. 11.40 uA, max. 21.18 uA)
8. If you receive a warning message stating that the calibration is questionable, do not continue with the
calibration. Instead, select ‘No’ and investigate what is causing the questionable results. If you accept a
questionable calibration, your DO readings will be erroneous. Typical causes of a calibration error message
include: incorrect sensor, membrane or port setup in the instrument, incorrect barometric pressure
information, a bad membrane or a sensor that needs reconditioned.
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