YSI 58 - Manual (Page 16)

In the discussion of calibration below instructions for Air Calibration are given for calibrating in the
% air saturation mode, while instructions for Air Saturated Water Calibration are given for calibrating
in the mg/L mode. Take note that either calibration technique can be performed in either mode. Use
of the percent air saturation mode is normally easier since the instrument automatically compensates
for temperature variation in that mode. The operator may nevertheless elect to calibrate in the mg/L
mode if he intends to make measurements in that mode, since doing so will eliminate any possible
mode-to-mode error. See final NOTE under both Air Calibration and Air Saturated Water
Calibration.
4.3.1 AIR CALIBRATION
Air Calibration is the quickest and by far the simplest calibration technique. Experience has shown
that it is reliable and is recommended for the YSI 58. Air Calibrate the YSI 58, with any field probe
as follows:
1.
Set the function switch to % Mode.
2.
To calibrate the probe, place a moist sponge or a piece of cloth in the plastic calibration
bottle. Loosen the bottle lid about ½ turn and slip the bottle over the probe guard up to the
body. Place the probe in a protected location where temperature is not changing, or wrap it in
a cloth or other insulator.
3.
The BOD probes can be placed in a BOD bottle containing about one inch of water to
provide a 100% relative humidity calibration environment.
4.
Remember that the highest accuracy of measurement is achieved when the probe is zeroed
and calibrated at a temperature as close as possible to the temperature of the sample to be
measured.
5.
Set the function switch to ZERO and readjust the display to read 0.00. Switch back to
percent air saturation mode.
6.
Determine the local altitude or the “true” atmospheric pressure. Using the pressure/altitude
chart, determine the correct CALIB VALUE for your pressure or altitude
Note: True atmospheric pressure is as read on a mercury barometer. Weather Bureau reporting of
atmospheric pressure is corrected to sea level.
7.
When the display reading has stabilized, unlock the 02 CALIB control locking ring and
adjust the display to the CALIB VALUE indicated in the pressure/altitude chart in Appendix
F. Relock the locking ring to prevent inadvertent changes.
NOTE: The oxygen content of air is affected by water vapor content. The use of air at 100% relative
humidity assures proper calibration. Moreover, air at less than 100% relative humidity can cause
evaporation of moisture from the probe’s temperature sensor, producing a local cooling effect. Errors
of up to 8% can result from calibrating in dry air.
NOTE: Should the user elect to air calibrate in the mg/L mode, Air Saturated Water Calibration steps
2-5 should be followed.
YSI Incorporated YSI 58 DO Meter 12