Global Water 800-876-1172 • globalw.com Global Water Instrumentation, Inc. 151 Graham Road P.O. Box 9010 College Station, TX 77842-9010 Telephone : 800-876-1172 International : (979) 690-5560, Fax : (979) 690-0440 e-mail : globalw@globalw.
Global Water 800-876-1172 • globalw.com Congratulations on your purchase of the Global Water WQ-FDO Optical Dissolved Oxygen Sensor. This instrument has been quality tested and approved for providing accurate and reliable conductivity and temperature measurements. We are confident that you will find this product to be a valuable asset for your application. Should you require assistance, our technical staff will be happy to help. Table of Contents I. Overview • • • • • • Page 3 II.
Global Water 800-876-1172 • globalw.com I. Overview The WQ-FDO Optical DO Sensor is an instrument designed for measuring dissolved oxygen in water. The optical DO sensors were developed to meet the requirements ranging from surface water monitoring programs to harsh waste water applications. The WQ-FDO has been specifically designed to meet the demanding requirements of the environmental monitoring and scientific research sectors, providing long term, accurate and reliable dissolved oxygen measurement.
Global Water 800-876-1172 • globalw.com A free software tool is available for use with Global Water’s family of data loggers that allows the WQ-FDO sensor’s two 4-20mA outputs to be monitored, along with optional conductivity and barometric pressure sensors, to determine the oxygen concentration and saturation levels. If the optional sensors are not used, provision is made for the hand entry of barometric pressure (or altitude) and conductivity (or salinity) into the calculation.
Global Water 800-876-1172 • globalw.com II. Sensor Specifications a. Specifications. Output Type: DO Range: Resolution: Accuracy: Drift: Temp. Range: Resolution: Accuracy: Service Life of Cap: Emersion Depth: Pressure Rating: Voltage Requirements: Supply Current: Warm Up Time: Response Time: Two 4-20mA outputs 0-400mbar @ 20ºC 0.1mbar +/- 0.5% <1% per year 0ºC to +50ºC (+32ºF to +122ºF) 0.01ºC (0.02ºF) 0.1ºC (0.2ºF) 1 Year minimum under normal use 6cm Minimum (2.
Global Water 800-876-1172 • globalw.com III. Cleaning and Maintenance Do not touch the sensor cap membrane with your fingers. Avoid any mechanical stress such as shock or vibration. Keep the outside of the sensor clean with tap water. Mild household detergent can also be used. Avoid cleaning in the area around the membrane. DO NOT use any cleaning products that contain alcohol. Use only a lint free microfiber cloth when cleaning the cap and membrane.
Global Water 800-876-1172 • globalw.com IV. Sensor Calibration The dissolved oxygen sensor should remain stable for the service life of the cap and membrane, which is greater than one year. This generally makes recalibration unnecessary. If the cap is replaced, recalibration should also not be necessary. The unique design of the FDO sensor allows a memory chip inside the cap to hold calibration information that is read by the sensor when a new cap is installed.
Global Water 800-876-1172 • globalw.com V. Converting Partial Pressure Measurements The calculation of dissolved oxygen concentration and saturation level is a complicated topic. Many variables affect the result including water and air temperature, conductivity or salinity, atmospheric pressure or altitude, and water vapor partial pressure. Some of these variables can’t always be calculated accurately and it is common to rely on empirical data rather than calculations.
Global Water 800-876-1172 • globalw.com Oxygen Concentration: First, calculate the oxygen concentration in mg/L (ppm) from the sensor’s partial pressure and temperature readings assuming zero salinity (Conductivity < 1000uS). C = PPO2 * [(6.906334E-2) – (1.797779E-3 * t) + (3.108257E-5 * t^2) - (2.
Global Water 800-876-1172 • globalw.com equations done by R.F. Weiss in 1970 and are generally considered to be a standard. These table entries will need to be corrected for salinity in the same way as the concentration above. Find the correction value from Tables 7.1 to 7.4. Multiply the oxygen solubility from tables 6.1 – 6.4 by the correction value to obtain the adjusted solubility. An equation can also be used, which is based on the work done by Weiss.
Global Water 800-876-1172 • globalw.com Other Calculations: Salinity: Salinity is a unitless number but is generally referred to in PSS (Practical Salinity Scale or PSU (Practical Salinity Units). Salinity can be calculated from conductivity by the equation: Salinity = A+(B*R^0.5)+(C*R)+(D*R^1.5)+(E*R^2)+(F*R^2.5) Where: A = 0.0120 B = -0.2174 C = 25.3283 D = 13.7714 E = -6.4788 F = 2.
Global Water 800-876-1172 • globalw.com VI. DO Solubility Lookup Tables Table 6.1 Solubility of Oxygen vs. Temperature (ºC) and Atmospheric Pressure (mbar) mbar 1059.6 1053.0 1046.3 1039.6 1033.0 1026.3 1019.6 1013.0 1006.3 999.6 993.0 986.3 979.6 973.0 966.3 959.7 953.0 946.3 939.7 933.0 0.0 15.3 15.2 15.1 15.0 14.9 14.8 14.7 14.6 14.5 14.4 14.3 14.2 14.1 14.0 13.9 13.8 13.7 13.6 13.5 13.4 0.5 15.1 15.0 14.9 14.8 14.7 14.6 14.5 14.4 14.3 14.2 14.
Global Water 800-876-1172 • globalw.com Table 6.2 Solubility of Oxygen vs. Temperature (ºC) and Atmospheric Pressure (mbar) mbar 1059.6 1053.0 1046.3 1039.6 1033.0 1026.3 1019.6 1013.0 1006.3 999.6 993.0 986.3 979.6 973.0 966.3 959.7 953.0 946.3 939.7 933.0 20.0 9.5 9.4 9.4 9.3 9.2 9.2 9.1 9.1 9.0 8.9 8.9 8.8 8.7 8.7 8.6 8.6 8.5 8.4 8.4 8.3 20.5 9.4 9.3 9.3 9.2 9.2 9.1 9.1 9.0 8.9 8.9 8.8 8.8 8.7 8.6 8.6 8.5 8.5 8.4 8.4 8.3 21.0 9.3 9.2 9.
Global Water 800-876-1172 • globalw.com Table 6.3 Solubility of Oxygen vs. Temperature (ºC) and Atmospheric Pressure (mbar) mbar 926.3 919.7 913.0 906.3 899.7 893.0 886.3 879.7 873.0 866.4 859.7 853.0 846.4 839.7 833.0 826.4 819.7 813.0 806.4 799.7 0.0 13.3 13.2 13.1 13.0 12.9 12.8 12.7 12.6 12.5 12.4 12.4 12.3 12.2 12.1 12.0 11.9 11.8 11.7 11.6 11.5 0.5 13.1 13.0 12.9 12.8 12.7 12.6 12.5 12.4 12.3 12.2 12.2 12.1 12.0 11.9 11.8 11.7 11.6 11.5 11.
Global Water 800-876-1172 • globalw.com Table 6.4 Solubility of Oxygen vs. Temperature (ºC) and Atmospheric Pressure (mbar) mbar 926.3 919.7 913.0 906.3 899.7 893.0 886.3 879.7 873.0 866.4 859.7 853.0 846.4 839.7 833.0 826.4 819.7 813.0 806.4 799.7 20.0 8.3 8.2 8.2 8.1 8.0 8.0 7.9 7.9 7.8 7.7 7.7 7.6 7.5 7.5 7.4 7.4 7.3 7.2 7.2 7.1 20.5 8.2 8.1 8.1 8.0 7.9 7.9 7.8 7.8 7.7 7.6 7.6 7.5 7.4 7.4 7.3 7.3 7.2 7.1 7.1 7.0 21.0 8.1 8.0 8.0 7.9 7.
Global Water 800-876-1172 • globalw.com VII. Salinity Correction Lookup Tables Table 7.1 Salinity Correction Factors for Dissolved Oxygen in Water vs. Temperature (ºC) and Conductivity (uS or PSS) uS 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000 15000 16000 PSS 0.0 0.5 1.0 1.6 2.1 2.7 3.3 3.8 4.4 5.0 5.6 6.2 6.8 7.5 8.1 8.7 9.3 0 1.000 0.996 0.992 0.988 0.984 0.981 0.977 0.973 0.969 0.965 0.961 0.957 0.953 0.950 0.946 0.
Global Water 800-876-1172 • globalw.com Table 7.2 Salinity Correction Factors for Dissolved Oxygen in Water vs. Temperature (ºC) and Conductivity (uS or PSS) uS 17000 18000 19000 20000 21000 22000 23000 24000 25000 26000 27000 28000 29000 30000 31000 32000 33000 PSS 10.0 10.6 11.3 11.9 12.6 13.2 13.9 14.5 15.2 15.9 16.5 17.2 17.9 18.6 19.2 19.9 20.6 0 0.934 0.930 0.926 0.922 0.918 0.914 0.910 0.906 0.902 0.897 0.893 0.889 0.885 0.881 0.877 0.873 0.
Global Water 800-876-1172 • globalw.com Table 7.3 Salinity Correction Factors for Dissolved Oxygen in Water vs. Temperature (ºC) and Conductivity (uS or PSS) uS 34000 35000 36000 37000 38000 39000 40000 41000 42000 43000 44000 45000 46000 47000 48000 49000 50000 PSS 21.3 22.0 22.7 23.4 24.0 24.8 25.5 26.2 26.9 27.6 28.4 29.1 29.8 30.5 31.3 32.0 32.7 0 0.865 0.861 0.857 0.853 0.849 0.844 0.840 0.836 0.832 0.828 0.824 0.820 0.815 0.811 0.807 0.803 0.
Global Water 800-876-1172 • globalw.com Table 7.4 Salinity Correction Factors for Dissolved Oxygen in Water vs. Temperature (ºC) and Conductivity (uS or PSS) uS 51000 52000 53000 54000 55000 56000 57000 58000 59000 60000 61000 62000 63000 64000 65000 66000 67000 PSS 33.5 34.2 34.9 35.7 36.4 37.2 37.9 38.7 39.4 40.2 40.9 41.7 42.5 43.2 44 44.8 45.6 0 0.795 0.791 0.787 0.782 0.778 0.774 0.770 0.766 0.762 0.757 0.753 0.749 0.745 0.741 0.736 0.732 0.
Global Water 800-876-1172 • globalw.com VIII. Trouble Shooting There are no user serviceable parts inside the WQ-FDO sensor, only the cap and membrane assembly can is replaceable a. b. c. d. Check all connections Inspect the cable for damage Check that the supply voltage is within specifications Make sure the dissolved oxygen and temperature of the solution is within the measurement ranges of the sensor e. Clean the sensor according to the guidelines described in the Cleaning and Maintenance section f.
Global Water 800-876-1172 • globalw.com IX. Warranty a. Global Water Instrumentation, Inc. warrants that its products are free from defects in material and workmanship under normal use and service for a period of one year from date of shipment from factory. Global Water’s obligations under this warranty are limited to, at Global Water’s option: (I) replacing or (II) repairing; any products determined to be defective. In no case shall Global Water’s liability exceed the products original purchase price.
Global Water 800-876-1172 • globalw.com X.
