48
O&M Manual
Rev-J (8/17)
Part 6 – Calibration
6.1 General
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, but it should be done during the initial installation.
The output of the optical dissolved oxygen sensor will degrade very slowly
over the lifetime of the optical element, which is normally 3-5 years. To
account for this degradation, the Q46D system should be re-calibrated
about every 6 months. 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 calibration schedule for a particular application. 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 2 hours to allow for
sensor stabilization and hydration of the optical element. Once the sensor
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),
% Saturation (air cal), and Zero. These three methods are significantly
different.
6.11 D.O. 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 Q46D 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.
