27
O&M Manual
Rev-L (7/15)
Part 6 – Calibration
6.1
Dissolved Oxygen Calibration
The instrument must be calibrated periodically to maintain a high degree of measurement
accuracy. A complete calibration will include zeroing and spanning the sensor. It is
generally unnecessary to set the zero at every calibration; however, it should be done
during the initial installation.
The output of the dissolved oxygen sensor will degrade over the cartridge lifetime as the
electrolyte and electrodes are slowly consumed. Under normal conditions (3 - 5 ppm) the
degradation occurs at a very slow rate. To account for this degradation, the Q45D system
should be re-calibrated at regular intervals. In addition, the frequency of calibration must
be determined by the application. High temperature applications or applications involving
other extreme operating conditions may require more frequent calibration than those
operating at more ambient levels. It is important for the user to establish a periodic
cleaning and calibration schedule for sensor maintenance. Before calibrating with a new
sensor for the first time, or whenever a sensor has been left unpowered for 10 days or
more, first connect the sensor to the transmitter and allow the system to operate for at
least 10 hours to properly polarize the cartridge electrodes. Failure to perform this
conditioning can result in significantly higher than normal initial readings. Once the
cartridge has been properly conditioned, the user must select the proper operating
parameters, including atmospheric pressure and solution conductivity.
The system provides three methods of D.O. calibration: 1-Point (sample), and Saturation
(air cal), and Zero. These three methods are significantly different.
6.2
Dissolved Oxygen Span Cal (1-spl)
The 1-Point (sample or comparison) method is intended to be primarily used as an on-
line calibration; however, the sensor can be removed, cleaned and then calibrated in a
bucket of clean water if necessary. During calibration, the system will display the current
ppm reading and the user can manually enter a reference value from a lab sample or
comparative reference instrument. In the Q45D system, the 1-Point calibration adjusts
the slope of the sensor output response.
1. Determine whether the calibration will be done on-line or with the sensor removed
and placed into a bucket of clean water. If the sensor is removed from the
application, rinse and clean if necessary.
2. If the sensor has been removed and placed into a bucket of water, allow sensor to
temperature equilibrate with the solution as much as possible. With the sensor coming
from an application which differs greatly in temperature, the user may have to wait as
much as 20 minutes. If the sensor is on-line, the user may want to set the output
HOLD feature prior to calibration to lock out any output fluctuations.
3. Scroll to the CAL menu section using the MENU key and press ENTER or the UP
arrow key.
Cal DO
will then be displayed.
4. Press the ENTER key. The screen will display a flashing
1-spl
for 1-point, a
2-sat
for
Saturation calibration, or a
3-zer
for zero calibration. Using the UP arrow key, set for
a 1-spl calibration and press ENTER.
