Using the YSI-85

The D.O. meter will be used to measure dissolved oxygen (DO), electrical conductivity, and salinity. The device measures six different water parameters, and is intended for use in moving water. The ``MODE'' button on the meter switches between the following in the order given below. Press the ``MODE'' button and wait for a few seconds for the mode to move to the next entry.

Note that D.O. is measured by the rate of consumption of oxygen at the tip of the probe, so it requires continual movement of water past the tip (an up-and-down motion seems to work best, keep the probe tip submerged). Stable readings will not be possible while the temperature of the sample is changing.

Figure 4.10: Dissolved oxygen-electrical conductivity-temperature meter (see manufacturer). Black probe is inserted into stream (or sample container) for measurement.

On/Off

Press the ON/OFF button to turn on the meter. The instrument will activate all segments of the display for a few seconds, which will be followed by a self-test procedure and will last for several more seconds. The Model 85 will display the cell constant of the conductivity probe when the self-test is complete (with ``CEL'' shown at the bottom of the LCD display). Then it will switch to D.O. % mode.

Temperature ( ${\rm ^\circ C }$)

always displayed as the last line in the readout

Dissolved Oxygen %

a measurement of oxygen in percent of saturation. If you are measuring D.O. in a bottled sample, stir with the probe so that water moves past it at a rate of around 1 $\rm\frac{ft}{sec}$. Wait until changes in reading are less than 1% over 15 seconds to record your reading.

Dissolved Oxygen $\rm\frac{mg}{L}$

a measurement of oxygen in $\rm\frac{milligrams}{liter}$ (same as parts-per-million)

Conductivity

a measurement of the conductive material in the liquid sample without regard to temperature (units are micro-siemens or $\mu S$). Be sure the two holes near the cable on the sensor are submerged; these make the conductivity measurement

Specific Conductance

also known as compensated conductivity which automatically adjusts the reading to a calculated value which would have been read if the sample had been at 25 ${\rm ^\circ C }$(units are micro-siemens or $\mu S$)

Salinity

a calculation done by the instrument electronics, based upon the conductivity and temperature readings (units are parts per thousand, or ppt)