YSI 55 - Manual (Page 12)

8
5. Calibration
Dissolved oxygen calibration must be done in an environment with a known oxygen content.
Since the amount of oxygen in the atmosphere is known, it makes an excellent environment for
calibration (at 100% relative humidity). The calibration/storage chamber contains a moist sponge
to create a 100% water saturated air environment.
5.1. Before You Calibrate
Before you calibrate the YSI Model 55, complete the procedures discussed in the Preparing the
Meter and Preparing the Probe chapters of this manual.
To accurately calibrate the YSI Model 55, you will need to know the following information:
• The approximate altitude of the region in which you are located.
• The approximate salinity of the water you will be analyzing. Fresh water has a salinity of
approximately zero. Sea water has a salinity of approximately 35 parts per thousand (ppt). If
you are not certain what the salinity of the sample water is, use a YSI Model 30 Salinity-
Conductivity-Temperature meter to determine it.
5.2. The Calibration Process
1. Ensure that the sponge inside the
instrument's calibration chamber is wet.
Insert the probe into the calibration
chamber.
CALIBRATION CHAMBER
2. Turn the instrument on by pressing the
ON/OFF button on the front of the
instrument. Wait for the dissolved oxygen
and temperature readings to stabilize
(usually 15 minutes is required after
turning the instrument on).
3. To enter the calibration menu, use two
fingers to press and release both the UP
ARROW and DOWN ARROW keys at
the same time.
4. The LCD will prompt you to enter the
local altitude in hundreds of feet. Use the
arrow keys to increase or decrease the
altitude.
EXAMPLE: Entering the number 12 here indicates 1200 feet.