How can the IntelliCAL™ LDO101 electrode accuracy be checked?

Document ID

Document ID TE3093

Published Date

Published Date 10/01/2019
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Question
How can the IntelliCAL™ LDO101 electrode accuracy be checked?
Summary
Accuracy check on IntelliCAL™ LDO101 probe
Answer
Although slope may be a good measure of accuracy on some probes, it is not a good measure of accuracy on our LDO and LBOD probes. (See also: What does the slope percentage indicate after a calibration on an IntelliCAL™ LDO101 Luminescent/Optical Dissolved Oxygen Probes?)

The best way to check the accuracy of a user calibration on an LDO or LBOD probe is to take a reading using the user calibration on an air saturated water sample. Since that sample should be 100% at a given temperature and pressure, one can use the DO charts to look up the theoretical mg/L reading at that measured temperature and pressure. (Please note, the probe does measure both temperature and pressure, and the units displayed can be changed in the meter to match the units used in the reference chart.)

There are two ways to do that. The easiest way to is take a reading on a 100% air saturated water sample after calibration. The difference between the displayed percentage of saturation and 100.0% can be interpreted as the percent error, since the reading should be 100.0% if the air saturated water sample was prepared correctly.

A more detailed way is to reference a table of theoretical DO values. Take a reading on a 100% air saturated water sample after calibration. Record the mg/L reading from the meter. Then, use the displayed temperature and pressure to look up the theoretical saturated DO for the corresponding temperature and pressure. Dividing the meter’s reading by the theoretical reading from the chart, then times 100, will give the calculated % saturation. The difference between that and 100.0% will give your percent error.

A quick, easy tool to use to determine what the theoretical dissolved oxygen value should be can be obtained off the USGS Dissolved Oxygen Solutibility Tables website.
Alternatively a table chart can be downloaded here: Dissolved Oxygen for Water, Wastewater, and Seawater

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