RDO Â® Optical Dissolved Oxygen Sensor - In-Situ Inc.

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Page 2 Installing the RDO Sensor 1. Install two D alkaline batteries in the TROLL 9500 instrument. 2. Remove the standard restrictor or Cal Cup from the TROLL 9500 instrument (if attached). This allows access to the sensor block. 3. Determine the installation port(s) for the RDO sensor. For the cable connect, choose port 1 or 3. For the direct connect, you must use both ports 2 and 3. Ports 1 and 4 will be available for other sensors. 7. 8. The cap's lifetime is 1 year after the first reading has been taken with the TROLL 9500 instrument. Install by the date printed on the packaging. Perform a 2-point calibration on the sensor, as described below. Attach the flow restrictor and nose cone. RDO Cable connect 4. 5. Cable connect Direct connect Use the Sensor Removal tool to remove the plug or existing sensor from the appropriate port(s). TIP: If installing the cable connector in port 3, you may wish to remove the port 2 sensor temporarily (if installed). Attach the RDO sensor to the TROLL 9500: a. For the direct connect sensor, remove the soft cap from the connector end of the RDO sensor. Plug the sensor pins into port 3. The sensor will overlap the white port plug and the dummy will sit in port 2. Proceed to step 6. b. For the cable connect sensor, insert the front end of the TROLL 9500 through the large hole in the adapter, alongside the RDO sensor. Direct connect 9. If using a cable connect sensor with a turbidity sensor or turbidity wiper, pull the slack in the adapter cable up against the probe so that it does not interfere with wiper movement or turbidity readings. Initial 2-Point CALIBRATION For best results, perform a 2-point calibration at 100% and 0% saturation before going into the field. Procedure 1. Connect the TROLL 9500 instrument to a PC or RuggedReader handheld PC. 2. Launch Win-Situ 4 or Pocket-Situ 4; and "Find" the device. Select the TROLL in the Navigation tree. The software will automatically detect and display the installed sensors. (This can take a moment.) 3. In the Navigation tree, under Parameters, click on Rugged Dissolved Oxygen. On the right side of the screen, click Calibrate. 6. c. Remove the soft cap from the connector end of the RDO cable. Using the alignment notch, align the 3-pin connector on the cable harness with the connector in the selected port (1 or 3) of the TROLL 9500 and press it firmly into the port until it sits flush with the instrument. d. Press down on the adapter until the instrument's sensor block is flush with the adapter plate surface. Align the RDO sensor between sensor ports 1 and 2. Align the open hole for the RDO sensor cable beside port 1. e. Tighten the adapter screw with a Phillips screwdriver. Do not overtighten. Remove the RDO sensor cap from its shipping/storage sleeve. Align the arrow with the index mark and firmly press the cap onto the sensor, without twisting, until it seals over the probe body. Make sure that the o-rings are not pinched or rolled between the cap and the sensor. Avoid allowing moisture, including atmospheric humidity, inside the cap. Keep the cap in its sealed packaging until you are ready to install it. Install promptly. Make sure that o-ring grooves are dry and the o-ring is not rolled or pinched inside the cap. 4. Three options appear. To perform a calibration, select the first or second option: • Calibrate: Starting from values stored in the sensor (user-set or factory defaults) for the 0% and 100% calibration, this allows the user to redo one or both calibration points • Restore defaults, then calibrate: Restores factory defaults for both 0% and 100%, then allows the user to redo one or both calibration points. • Restore defaults, don't calibrate: Restores factory defaults for both 0% and 100% saturation and closes the Calibration Wizard.
Page 3 Indicators During Calibration • Status: NOT TESTED is displayed until you begin the calibration by selecting Run. UNSTABLE indicates the sensor response does not yet meet the criteria for a valid calibration point. NOMINAL indicates the sensor deviation meets early stabilization criteria. The Accept button becomes available when nominal stability is achieved. You may accept the early value or wait for complete stability. If you accept the early value, the calibration point will be designated “USER SET” in the calibration report. STABLE is displayed when the readings have stabilized sufficiently to take a valid calibration point. The calibration proceeds automatically to the next screen. • Reading: The current sensor response in mg/L and degrees Celsius. • Deviation: Change in sensor response between the last two readings. This enables you to follow the progress of the stabilization, but deviation from the previous reading is not necessarily the best indicator of stability as the software is looking at longer-term trends. • Barometric Pressure is shown in your selected unit. Preparation for 100% Oxygen Calibration 100% DO calibration is performed in water saturated with air. We recommend a container of clean water aerated with the In-Situ RDO bubbler cal kit (see Replacement Parts list) or an aquarium pump. Fill the bubbler cup with clean water. Turn on the pump and regulate with the pinch valve. Insert the TROLL 9500 instrument into the bubbler, resting the RDO adapter plate on the rim of the cup. Ensure that the temperature sensor is submerged at least ½ in, and the RDO sensing foil is not in the direct path of the bubbles. 5. After allowing 5 – 10 minutes for temperature stabilization, click the Run button. Follow the on-screen instructions to complete the 100% calibration point. 6. Continue with the 0% Oxygen Calibration for a 2-point calibration or select Next, then Finish to finalize the calibration. Preparation for 0% Oxygen Calibration 0% D.O. calibration is performed in an oxygen-depleted solution. Sodium sulfite (Na 2 SO 3 , see Replacement Parts list) is available from In-Situ Inc. Bubbled nitrogen may be used; in this case allow plenty of time for the oxygen to be completely purged from the water. Units and Calculated Measurements Four units of measurement are available for DO: TIP: To change unit preferences: In Win-Situ 4, select Preferences on the Options menu. In Pocket-Situ, select the Home site, then tap Setup in the command bar. • Oxygen concentration in milligrams of oxygen per liter of water (mg/L). Since a liter of pure water weighs 1000 grams, and a milligram is 1/1000 of a gram, this is equivalent to ppm (parts per million). • Oxygen concentration in micrograms of oxygen per liter of water (µg/L). This is equivalent to parts per billion (ppb). • Oxygen concentration in microMolar (µmol/L) = mg/L x 31.25 • Oxygen saturation in % —100% DO being the maximum (equilibrium) amount of oxygen that can be dissolved in water at a given atmospheric pressure, water temperature, and salinity. The percent saturation output is automatically corrected using the TROLL 9500 instrument's temperature, conductivity, and barometric pressure values (from a barometric sensor on vented cable or from a user-entered input). If no conductivity sensor is present, salinity is assumed to be zero. USAGE RECOMMENDATIONS AND CAUTIONS The amount of oxygen that can be dissolved in water decreases at higher temperatures and with increasing altitude (i.e., as barometric pressure drops) and salinity. In other words, as water becomes warmer and saltier, it can hold less DO. During tests that include the RDO channel, the TROLL 9500 instrument automatically measures barometric pressure and temperature for compensation of DO readings. The barometric pressure value at the time of calibration is stored in the sensor and will be used to correct DO readings for weather-induced pressure fluctuations taken at the same relative barometric pressure as the calibration. However, the large changes in barometric pressure due to changes in elevation are best accommodated by performing a recalibration. If you calibrate at sea level, for example, and deploy the instrument in the mountains, you should perform a recalibration at the new altitude. Exposure to direct sunlight can bleach the sensing foil over time but this effect is minimized with the protection provided by the opaque optical isolation layer. However, the frequent application of strong blue light (blue LED during readings) will eventually have a bleaching effect on the foil. In-Situ recommends sampling intervals of greater than 1 minute for longterm deployments. Warning: The RDO sensor is not compatible with organic solvents. Salinity Since the absolute solubility of oxygen is lower in saline waters, it is advantageous to compensate DO concentration readings (µg/L, mg/L, µmol/L) to ensure that the sensor accurately reports the concentration of DO in the presence of significant salinity. This can be accomplished by storing a salinity value in the sensor before taking measurements. The compensation algorithm is applied internally before the concentration is reported. The degree of compensation is minimal at very low salinities, and but may affect readings by several percent at higher levels. To store a salinity value in the RDO sensor, connect in Win-Situ 4 or Pocket-Situ 4, select RDO in the Navigation tree, click Edit and in the next screen select "Edit RDO Salinity Value."
Page 1: TROLL ® 9500 Water Quality Instrum

RDO Â® Optical Dissolved Oxygen Sensor - In-Situ Inc.

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