YSI 550A - Manual (Page 10)

Page 6
Y S I
Environmental
YSI 550A
DISSOLVED OXYGEN CALIBRATION
Dissolved oxygen calibration must be done in an environment with known oxygen content. The
YSI 550A DO Instrument can be calibrated in either mg/L or % saturation. Sections below include
instructions on how to calibrate in either mode.
BEFORE YOU CALIBRATE
To accurately calibrate the YSI 550A, you will need to know the following information:
• The approximate salinity of the water you will be analyzing. Fresh water has a salinity of
approximately zero. Seawater has a salinity of approximately 35 parts per thousand (ppt). If you are
uncertain what the salinity of the sample water is, use a YSI 30 Salinity-Conductivity-Temperature
instrument to determine a salinity value.
• For calibration in % saturation mode, the approximate altitude (in feet) of the region where you are
located is required. This information can be obtained over the internet or from a local airport or
weather station. To convert from meters to feet, divide by 0.3048.
For best results:
• Check calibration with each use and recalibrate as necessary to prevent drift. Dissolved oxygen
readings are only as good as the calibration.
CALIBRATION IN % SATURATION
1.
Ensure that the sponge inside the instrument's calibration chamber is moist. Insert the probe into
the calibration chamber.
2.
Power the instrument on and allow readings to stabilize. This may take 5 to 15 minutes, depending
on the age of the instrument and condition of the probe.
3.
Press and release both the UP ARROW and DOWN ARROW keys at the same time to enter the
calibration menu.
4.
Press the Mode key until “%” is displayed on the right side of the screen for oxygen units. Press
ENTER.
5.
The LCD will prompt you to enter the local altitude in hundreds of feet. Use the arrow keys to
increase or decrease the altitude. When the proper altitude appears on the LCD, press the ENTER
key.
EXAMPLE: Entering the number 12 here indicates 1200 feet.