HQd LDO-Calibration From User Manual 3ed 03-2006

71 Section 8 LDO Operation and Methods 8.1 Taking a Dissolved Oxygen Measurement If complete traceability is required, enter a Sample ID and Operato r ID before measurin g. Note: The default setting for Measurement Mode is “Press to Read”. To change the mode, see Measurement Mode in section 9.5 on page 84. Important Note: A count down message appears on the screen thirty days before the sensor-cap expiration date. This message will continue to display until there are zero days remaining and the sensor cap must be replaced. All measurements taken after the sensor cap expiration date appear with the calibration ? icon at the top left corner of the screen. 1. Place the LDO probe into the sample. 2. Press the GREEN/RIGHT key under Read. 3. The display will show “Stabilizing…” and a progress bar will fill from 0 to 100% as the probe stabilizes in the sample. When the result has stabilized, the lock icon will appear and the result will be stored automatically in the data log. 4. T o make another measurement, repeat this procedure. The display will also show the temperature and pressure. If a salinity correction was entered, the correction will appear on the displ ay . 8.2 Calibrating the LDO Probe Important Note: Factory calibration is the default setting. Factory calibration coefficients are stored in the iButton ® *. Each lot of LDO sensor caps is factory calibrated. Performance will vary slightly as a function of usage history . For best performance, a one-time calibration initialization can be performed when a new sensor is installed. Additional calibrations can be performed at the operator's discretion but are not required. Manually calibrating the LDO probe will require creating and modifying a new method (see section 8.4 on page 74 ). LDO calibration can be performed manually using one of two standards: Water-saturated air (recommended). For example, use a bottle with a narrow neck such as a BOD bottle (Cat. No. 621-00). Add a small amount (1-cm) of water to the bottle, stopper and shake vigorously for several minutes, then insert the probe. • A water sample with a known dissolved oxygen concentration. The concentration must be determined by Winkler titration, or by calculation of a saturated-air water sample using existing pressure, temperature, and salinity conditions. Note: Modify the LDO Method to use a water sample as a s tandard. * iButton is a registered trademark of Maxim Inte grated Products, Inc.

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HQd LDO-Calibration From User Manual 3ed 03-2006