OBS-3A Turbidity and Temperature Monitoring System Revision: 7/13 C o p y r i g h t © 2 0 0 7 - 2 0 1 3 C a m p b e l l S c i e n t i f i c , I n c .
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Table of Contents PDF viewers: These page numbers refer to the printed version of this document. Use the PDF reader bookmarks tab for links to specific sections. 1. Introduction .................................................................1 2. Cautionary Statements...............................................1 3. Initial Inspection .........................................................1 3.1 Ships With............................................................................................2 4.
Table of Contents 6.13 6.14 Excel Spreadsheets ............................................................................ 41 Erasing Memory Data........................................................................ 42 7. Calibration .................................................................43 7.1 Turbidity............................................................................................ 43 7.1.1 Equipment and Materials............................................................ 43 7.
Table of Contents Tables 6-1. 7-1. 7-2. 9-1. Working and Maximum Depths ...........................................................7 Mixing Volumes for Formazin Standards ..........................................46 Sample Durations for Sediment Calibrations .....................................48 Battery Life (Hours)...........................................................................
Table of Contents iv
OBS-3A Turbidity and Temperature Monitoring System 1. Introduction The OBS-3A combines our OBS® probe with pressure, temperature, and conductivity sensors in a battery-powered recording instrument. Batteries and electronics are contained in a housing capable of operating at depths of up to 300 meters—depending on the pressure sensor installed. Before installing the OBS-3A, please study: • • 2. 3.
OBS-3A Turbidity and Temperature Monitoring System 3.1 Ships With CSI pn 21229 Accessory Kit ResourceDVD CSI pn 29225 HydroSci Software on DVD 4. Overview The heart of the OBS-3A is an OBS® sensor for measuring turbidity and suspended solids concentrations by detecting near infrared (NIR) radiation scattered from suspended particles. With a unique optical design, OBS sensors perform better than most in situ turbidity sensors in the following ways: 1. Small size and sample volume, 2.
OBS-3A Turbidity and Temperature Monitoring System FIGURE 4-1. Anatomy of an OBS sensor 4.2 Temperature and Optional Sensors Temperature is measured with a fast-response, stainless steel-clad thermistor. Pressure is measured with a semiconductor piezoresistive strain gage. Conductivity is measured with a four-electrode conduction-type cell. Working depths for available pressure sensors are listed in TABLE 6-1. 4.
OBS-3A Turbidity and Temperature Monitoring System Light transmission in water is attenuated by scattering (deflection by water molecules, and suspended matter) and absorption, which converts light to heat. Attenuation, absorption, and scattering are inherent properties of water that are affected only by impurities such as color and suspended organic matter. Optically pure water is not readily available; however deionized water that has passed through a 0.2 µm filter is adequate for most practical purposes.
OBS-3A Turbidity and Temperature Monitoring System 5.1 5.2 5.3 5.4 Measurement Range Turbidity (AMCO Clear): 0.4 to 4,000 NTU1 Mud (D50=20 µm): 0.4 to 5,000 mg/L Sand (D50=250 µm): 2 to 100,000 mg/L Pressure2: 0 to 10, 20, 50, 100, or 200 m Temperature: 0° to 35°C Conductivity (salinity): 0 to 65 mS/cm (40 PSU, o/oo) 1 0 to 100, 0 to 250, 0 to 500, 0 to 1000, 0 to 2000, and 0 to 4000 NTU ranges are available. 2 Range depends on pressure sensor option chosen.
OBS-3A Turbidity and Temperature Monitoring System Battery capacity: 18 A h Maximum battery life: 8,000 hours Data protocols: RS-232 / RS-485 Maximum housing depth: 300 m (984 ft) Infrared wavelength: 850 nm Operating temperature range: 0° to 35°C Storage temperature range: –20° to 70°C 5.5 Physcial Length / diameter: 362 mm (14.3 in) / 76 mm (3.0 in) Weight (w/o batteries): 1.5 kg (3.4 lb) Weight (submerged): 0.2 kg (0.5 lb) 362 mm (14.3 in) USE HOSE CLAMPS HERE ↑ 76 mm (3.
OBS-3A Turbidity and Temperature Monitoring System TABLE 6-1. Working and Maximum Depths Pressure Sensor Working Depth Maximum Depth 0.
OBS-3A Turbidity and Temperature Monitoring System the cable grip and connector and put chafe protection on the sensor head where it contacts the wire rope. FIGURE 6-1. Components 6.1.2 Battery Installation If unit is wet, perform the following operations with the unit held sensor end up. Remove the three hex screws from the end with the handle and pull the cap down and out of the housing.
OBS-3A Turbidity and Temperature Monitoring System FIGURE 6-2. Battery installation For extended deployment time, lithium batteries are a good alternative to alkaline batteries. Campbell Scientific sells a D-cell-sized battery spacer (pn 21906) that allows lithium D-cell batteries to be used with the OBS-3A. Lithium D-cell batteries have a higher voltage than their alkaline counterparts, necessitating the spacer. Campbell Scientific does not sell lithium D-cell batteries. 6.
OBS-3A Turbidity and Temperature Monitoring System 6.3 Running HydroSci 1. Select the HydroSci program to start the program. 2. Physically connect the OBS-3A to a PC with the test cable as shown in FIGURE 6-3. This can be an RS-232, RS485, or USB plug. FIGURE 6-3.
OBS-3A Turbidity and Temperature Monitoring System 3. Select OBS-3A on the lift side of the screen and select the appropriate COM Port and Baud Rate at which to communicate. Press the Connect button. 4. Upon successful connection, the Monitor screen will appear: 5. Synchronize the OBS-3A clock with your PC by clicking Set OBS-3A Time. 6. Configure your OBS-3A as desired. For more information on configuration options, see Section 6.8, OBS-3A Configuration.
OBS-3A Turbidity and Temperature Monitoring System 7. 6.4 After you have finished interacting with your sensor, click on the Connection tab and press the Disconnect button to disconnect from your sensor. Testing Sensors Before daily operations and deployments, verify the instrument works by pressing Survey Configuration and Start Survey. Then press Monitor to see the plot.
OBS-3A Turbidity and Temperature Monitoring System Blow on the temperature sensor to observe an increase in temperature (red trace line on the top plot). Dip the sensor in salty water and conductivity will increase (aqua trace line on the top plot). Wave your hand in from of the OBS sensor; the turbidity signal will fluctuate and data will scroll (green trace line on the middle plot). Blow into the pressure sensor and a small elevation in the pressure signal will occur (blue trace line on bottom plot).
OBS-3A Turbidity and Temperature Monitoring System Show Terminal tab brings up a terminal screen that allows you to view the commands being sent to the OBS-3A and the responses that are returned. 6.7 Connection The default communication settings are: 115 kbps, 8 data bits, no parity, no flow control. These settings will work for most applications and with most PCs. If the OBS-3A does not connect this screen will appear: If the OBS-3A is sampling, you have the option to stop the test.
OBS-3A Turbidity and Temperature Monitoring System 6.8.2 Operations Put OBS-3A to Sleep Press the Sleep button to put the OBS-3A in low-power, sleep mode. This should be done when the OBS-3A will not be used for an extended period of time to conserve battery capacity. Use the drop-down button to specify how often the OBS-3A will wake to check for communication.
OBS-3A Turbidity and Temperature Monitoring System HydroSci will confirm if you want to put the OBS-3A to sleep. Clear OBS-3A Data Storage Press the Erase Flash Button to clear all data stored in the OBS-3A. HydroSci will confirm you want to clear all the data stored. Stop Current Operation Press the Stop button to end any operation currently running in the OBS-3A. Baud Rate Setting Specifies the baud rate at which the OBS-3A will communicate.
OBS-3A Turbidity and Temperature Monitoring System Barometric Correction The OBS-3A measures absolute pressure so a correction must be made for barometric pressure. Press the Run Correction button to run a barometric pressure correction. NOTE Be sure to do this while the OBS-3A is at the surface. Doing so when the instrument is submerged will result in large errors in the depth measurement.
OBS-3A Turbidity and Temperature Monitoring System Change to RS-232 To switch from RS-485 communication to RS-232 communication, press the RS-232 button and then remove the RS-485 converter. NOTE Once the button is pressed, you will no longer be able to communicate via RS-485. However, if you accidently push this button, the OBS-3A can be reset by removing and reinserting the batteries.
OBS-3A Turbidity and Temperature Monitoring System If it becomes necessary to load coefficients from a saved file, press the Load Coefficients from File button. Select the appropriate file from the resulting browsing window and press Open. You will be asked to confirm that you really want to replace the coefficients from the corresponding sensor. Press Yes and the coefficients from the file will be loaded into the OBS-3A.
OBS-3A Turbidity and Temperature Monitoring System Calibration The Calibration box can be used to calibrate the OBS-3A for NTU or mg/L measurements. Press the Calibrate button. You will be asked to select NTU or mg/L. After selecting the units, you will be taken to the calibration screen. For more information on calibration, detailed procedures are found in in Section 7, Calibration. 6.8.
OBS-3A Turbidity and Temperature Monitoring System You will be asked whether or not you want to log data to a file on your computer. NOTE In survey mode, data is not saved to the OBS-3A. Data will not be saved if you choose not to log data to a file. After the survey is started, you can select the Monitor tab to view the data. When you have finished logging data, return to the OBS-3A Configuration tab and press the Stop Survey button to stop the survey.
OBS-3A Turbidity and Temperature Monitoring System You can press the Load Configuration From File button to load a configuration that has previously been saved. The configuration can then be edited and/or started in the OBS-3A.
OBS-3A Turbidity and Temperature Monitoring System Units of Measure Select the units for depth (Meters or Feet). Sensor Measurements Select the check boxes next to the sensor measurements you wish to make. Water Density Specify the water temperature and salinity. The specified temperature and salinity only affect the depth calculation. They do not influence temperature or salinity measurements. Data Logging Rate Rate is the frequency of sampling. Select 12, 30, 60, or 120 lines per minute. 6.8.
OBS-3A Turbidity and Temperature Monitoring System You will be asked whether or not you want to log data to a file on your computer. After setting the parameters, you can also press the Save Configuration To File button to save the configuration to be used at a later time. You can press the Load Configuration From File button to load a configuration that has previously been saved. The configuration can then be edited and/or started in the OBS-3A.
OBS-3A Turbidity and Temperature Monitoring System • NOTE Wave Setup Wave Setup fields are only enabled when Depth is selected under Sensor Measurements and the Depth Statistics is set to Depth, Hs, Ts. o Record Length When wave measurements are selected, this sets the time in seconds for which depth measurements are made for the wave-spectral computations. Use a record length of 512 seconds for inshore waters (lakes and rivers), protected bays and estuaries.
OBS-3A Turbidity and Temperature Monitoring System o Rate Rate is the frequency of sampling for the duration of measurements. All sensors are sampled at the same rate, typically 2, 5, 10, or 25 times per second (Hz). For example, a rate of 25 Hz for a 60-second duration will produce a sample with 1500 measurements for each sensor. When wave statistics are chosen, the rate must be selected in the Wave Setup box. o Duration This is the length of time in seconds that the OBS-3A is measuring its sensors.
OBS-3A Turbidity and Temperature Monitoring System Go to the Connection tab and press Disconnect to disconnect from the OBS3A. Unplug the test cable. Install dummy plug and locking sleeve. The instrument is then ready for deployment. After setting the parameters, you can also press the Save Configuration To File button to save the configuration to be used at a later time. You can press the Load Configuration From File button to load a configuration that has previously been saved.
OBS-3A Turbidity and Temperature Monitoring System • Water Density Specify the water temperature and salinity. The specified temperature and salinity only affect the depth calculation. They do not influence temperature or salinity measurements. • NOTE Wave Setup Wave Setup fields are only enabled when Depth is selected under Sensor Measurements and the Depth Statistics is set to Depth, Hs, Ts.
OBS-3A Turbidity and Temperature Monitoring System • Sample Settings o Duration This is the length of time in seconds that the OBS-3A is measuring its sensors. The duration must always be less than the interval. The minimum duration is five seconds and the maximum is the longer of the wave record length or the 2048 / rate. NOTE The product of the rate and the duration cannot exceed 2048. o Rate Rate is the frequency of sampling for the duration of measurements.
OBS-3A Turbidity and Temperature Monitoring System 6.8.6 Setpoint Configuration Setpoint Configuration mode is used for fast sampling of events such as storms, floods, dredging operations, and construction activities. The unit will revert to slow recording between events. Sample events two to five times faster than the rate chosen for the periods between events.
OBS-3A Turbidity and Temperature Monitoring System • Sensor Measurements Select the check boxes next to the sensor measurements you wish to make. For Depth and OBS (NTU) use the drop-down boxes next to Statistics to select the desired statistics for the measurement. • Units of Measure Select the units for depth (Meters or Feet). • Water Density Specify the water temperature and salinity. The specified temperature and salinity only affect the depth calculation.
OBS-3A Turbidity and Temperature Monitoring System • Interval Settings o Slow Interval The time, in seconds, between the start of one sample and the beginning of the next, when an event is not occurring. The interval must be longer than the duration plus some time for statistical computations. HydroSci will prompt you if too short an interval is selected. o Fast Interval The time, in seconds, between the start of one sample and the beginning of the next, when an event is occurring.
OBS-3A Turbidity and Temperature Monitoring System Temperature, Salinity, Concentration, and Depth are shown on the charts. Only the sensor measurements that were chosen in the configuration will be shown. (Temperature and Salinity are shown as different traces on the same chart. The temperature scale is on the left axis, and the salinity scale is on the right axis.) You can change chart properties by pressing the Chart Properties button.
OBS-3A Turbidity and Temperature Monitoring System All sensor measurements selected in the configuration will be shown in the table view. Use the scroll bar to scroll through the data. Select the Pause Data Output check box to temporarily pause the table from updating. If a survey is not currently running, the Monitor screen shows the current Sensor Time and PC Time. Press the Set OBS-3A Time button to set the OBS-3A time to the current PC time.
OBS-3A Turbidity and Temperature Monitoring System 6.10 View Data The View Data screen can be used to view data stored on the OBS-3A from cyclic, scheduled and setpoint surveys. (When running in survey configuration, data is not stored to the OBS-3A.) All of the available files will be shown in the List of Data Files. Click on a file in the list to have its contents displayed in Data File Contents.
OBS-3A Turbidity and Temperature Monitoring System 3. A screen asking if the OBS-3A is currently sampling will appear. If you are ready to stop sampling, select radio button Stop sampling data. If you are not ready to stop, select Let the sample continue to run. If you selected Stop sampling data, a screen will appear saying The OBS-3A has been successfully stopped. Press OK. Otherwise, Let the sample continue to run will ask you if you would like to log data to a file? Select Yes or No.
OBS-3A Turbidity and Temperature Monitoring System 4. Go to View Data to save data in a file. 5. Highlight the data with the start and end times you want. The Data File Contents shows a preview of the data you have selected. You can also click View Data File to view the complete data file.
OBS-3A Turbidity and Temperature Monitoring System 6. Once the correct data is selected, press Save Data File. The Save As screen will appear, name your file and press Save. When viewing data within View you have the ability to view, graph and print the data from the file. 6.10.2 Graphing and Printing To graph the data, select which columns you wish to display. They will be highlighted when selected.
OBS-3A Turbidity and Temperature Monitoring System Then press the New Line Graph various graphing options. button and a new screen will appear with Categories can be selected and unselected to appear in the graph. Graph Width allows you to select the period the graph is showing and adjust how many data points show at once. Printing buttons.
OBS-3A Turbidity and Temperature Monitoring System . The spreadsheet of data can also be printed. 6.11 Show Terminal The Show Terminal tab brings up a terminal screen that allows you to view the commands being sent to the OBS-3A and the responses that are returned.
OBS-3A Turbidity and Temperature Monitoring System 6.12 Shutdown From the OBS-3A Configuration | Operations tab, select Put OBS-3A To Sleep. It will ask you to confirm your request. Press Yes and the OBS-3A will disconnect from HydroSci. You are then able to unplug your sensor. 6.13 Excel Spreadsheets To make an Excel spreadsheet from OBS-3A data, start Excel and set file type to All. Open a data file and select Delimited in Step 1 of 3 of the Text Import Wizard.
OBS-3A Turbidity and Temperature Monitoring System 6.14 Erasing Memory Data To erase the memory data on the OBS-3A, go to OBS-3A Configuration | Operations | Clear OBS-3A Data Storage | Erase Flash. It will have you confirm that you wish to erase all the data from the OBS-3A.
OBS-3A Turbidity and Temperature Monitoring System 7. Calibration It is a good idea to use the Retrieve and Save Coefficients to File button (under Operations on the OBS-3A Configuration screen) to save the original coefficients before performing a calibration. 7.1 Turbidity This section briefly describes the materials and equipment you will need and the basic procedures for calibrating OBS sensors with AMCO Clear and sediment.
OBS-3A Turbidity and Temperature Monitoring System • 100 ml to deliver (TD) volumetric pipette • 25 ml TD measuring pipette • 2 gallons filtered distilled water (purified water from the super market works fine) • Slotted stainless steel stirring spoon 1. Experience has shown that only three calibration points are needed to get sub-1% accuracy.
OBS-3A Turbidity and Temperature Monitoring System WARNING 3. Prepare the next NTU standard and put the OBS-3A in it. Repeat steps 1 and 2 for all calibration values. 4. After all calibration values have been recorded, click the Calculate Fit button. 5. Look at the plot of residuals (blue line) which shows the differences between the standard and computed NTU values.
OBS-3A Turbidity and Temperature Monitoring System The formula for preparing turbidity standards other than shown in TABLE 7-1 is: ⎡ Vstk ⎤ Tstd = Tstk ⎢ ⎥ ⎣Vdw + Vstk ⎦ ⎡ Tstd × Vdw ⎤ Vstk = ⎢ ⎥ ⎣ Tstk − Tstd ⎦ or Where: Tstd = Turbidity of the standard solution; Tstk = Turbidity of the stock solution, usually 4000 NTU; Vstk = Cumulative volume of stock solution at each calibration point; Vdw = Initial volume. TABLE 7-1. Mixing Volumes for Formazin Standards 7.
OBS-3A Turbidity and Temperature Monitoring System 7.2.1 Equipment and Materials • Dry, completely disaggregated bottom sediment or suspended matter from the monitoring site, • 1-gallon (4 L) brown Nalgene polypropylene bottle with top cut off, • 1-liter, Class A volumetric flask, • 2 gallons filtered distilled water (purified water from the super market works fine), • Hand-drill motor, • Paint stirrer. 7.2.2 Sediment Preparation Sediment preparation is a critical factor in calibration quality.
OBS-3A Turbidity and Temperature Monitoring System 60 50 Turbidity (NTU) 40 3-min. Sonic Probe 30 15-min. Sonic Bath 20 Hand Shaking 10 0 10 20 30 40 Sediment Concentration (mg/l) 50 FIGURE 7-1. Effects of disaggregation Preparation 1. Clean containers and glassware with detergent and rinse with filtered water. 2. Perform the calibration under fluorescent lighting. 3. Based on the material, select the appropriate sample duration from TABLE 7-2. TABLE 7-2.
OBS-3A Turbidity and Temperature Monitoring System Sediment concentrations are calculated with the following equations: Ms = mg/l ⎡ Ms ⎤ Vi + ⎢ ⎥ ⎣ ρs ⎦ ; Ms = ppm Mi + Ms Where: Ms = Mass (mg) of sediment in suspension Mi = Initial water mass, 1× Vi ( kg ) Vi = Initial volume (L) ρ s = Sediment density (usually 2.65 × 10 3 mg / l ) 7. For the zero calibration point you will need a clean black 20 x 14 x 16 inch container filled with clean tap water. A Rubbermaid® plastic storage box is suitable. 8.
OBS-3A Turbidity and Temperature Monitoring System FIGURE 8-1. Component locations Unit does not communicate with PC. There are several possible causes for this symptom. 1. The test/umbilical cable is damaged or improperly connected. 2. The OBS-3A is sleeping and will not wake up. 3. The batteries are dead. 4. The OBS-3A and PC are not set to the same baud rate or communication protocol (RS-232, USB, RS-485). a. 50 Click and check COM port settings on the Connection tab.
OBS-3A Turbidity and Temperature Monitoring System b. If the OBS-3A still fails to respond, try changing baud rate speeds by selecting Attempt to find the baud rate to communicate. If this fails, switch the PC back to 115.2 kB and go to the next step. c. Reconnect the cable and try to connect again. d. Replace the main batteries; see Section 6.1.2, Battery Installation, and try to connect again. e. If you have a survey cable, connect instrument to external power and try to connect again. f.
OBS-3A Turbidity and Temperature Monitoring System Power failed due to battery clip corrosion or a broken power wire. Check for a broken red wire connecting the battery tube and circuit board. Green powder or tarnish on the battery contact parts indicates salt-water corrosion. Remove the electronics from the pressure housing. Pull batteryclip-retainer pin out with needle-nose pliers and slide the clip from its track. Clean the corroded surfaces of clip and track with a Scotch-brite® pad and reassemble unit.
OBS-3A Turbidity and Temperature Monitoring System 9. Maintenance 9.1 OBS Sensor The OBS sensor must be kept clean to measure sediment concentration or turbidity accurately. A gradual decline in sensitivity over a period of time indicates fouling with mud, oil, or biological material. Regular cleaning with a water jet, mild detergent and warm water, or a Scotch-brite® abrasive pad will remove most contaminants encountered in the field.
OBS-3A Turbidity and Temperature Monitoring System during surveys or after each deployment. A sensor that has been stored dry should be soaked in water for 15 minutes prior to use. If the sensor becomes fouled with sediment, oil, or biological material, conductivity will decline over a period of time indicating cleaning is necessary. If a water jet fails to remove contaminants, the sensor can be flushed with hot soapy water or warm alcohol. Do not use solvents.
OBS-3A Turbidity and Temperature Monitoring System 9.5 Pressure Housing The pressure housing and O-ring seals require little maintenance unless the housing has been opened since the last service. However, it should be carefully inspected every six months and serviced before all deployments longer than one month. 9.6 1. Disassemble O-ring seals and inspect mating surfaces for pits and scratches. 2. Inspect O-rings for cuts and nicks; replace if necessary using spares provided. 3.
OBS-3A Turbidity and Temperature Monitoring System 10.1 Particle Size The size of suspended sediment particles typically ranges from about 0.2 to 500 µm in surface water (streams, estuaries and the ocean). Everything else being equal (size, shape, and color), particle area normal to a light beam will determine the intensity of light scattered by a volume of suspended matter.
OBS-3A Turbidity and Temperature Monitoring System 10.2 Suspensions with Mud and Sand As mentioned earlier, backscattering from particles is inversely related to particle size on a mass concentration basis (see FIGURE 10-2). This can lead to serious difficulties in flow regimes where particle size varies with time. For example, when sandy mud goes through a cycle of suspension and deposition during a storm, the ratio of sand to mud in suspension will change.
OBS-3A Turbidity and Temperature Monitoring System 10.3 High Sediment Concentrations At high sediment concentrations, particularly in suspensions of high clay and silt, the infrared radiation from the emitter can be so strongly attenuated along the path connecting the emitter, the particle, and the detector, that backscatter decreases with increasing sediment concentration. For mud, this occurs at concentrations greater than about 5,000 mg/L.
OBS-3A Turbidity and Temperature Monitoring System 10.4 Sediment Color Sediment color, after particle size, has a major effect on OBS sensitivity, and if it changes, it can degrade the accuracy of measurements. Although OBS sensors are “color blind”, “whiteness”, color, and IR reflectivity (measured by an OBS sensor) are well correlated.
OBS-3A Turbidity and Temperature Monitoring System 10.6 Bubbles Although bubbles efficiently scatter IR, monitoring in most natural environments shows that OBS signals are not strongly affected by bubbles. Bubbles and quartz particles backscatter nearly the same amount of light to within a factor of approximately four, but most of the time bubble concentrations are at least two orders of magnitude less than sand concentrations in most environments.
OBS-3A Turbidity and Temperature Monitoring System 10.7 Biological and Chemical Fouling Sensor cleaning is essential during extended deployments. In salt water, barnacle growth on an OBS sensor can obscure the IR emitter and/or detectors and produce an apparent decline in turbidity. Algal growth in marine and fresh waters has caused spurious scatter and apparent increases of OBS output. The reverse has also been noted in fresh water where the signal increases after cleaning the sensor window.
OBS-3A Turbidity and Temperature Monitoring System Standard Methods for the Examination of Water and Wastewater, 20th Edition. 1998. 2130 Turbidity. American Public Health Association et al. Washington, DC. Standard Methods for the Examination of Water and Wastewater, 20th Edition. 1998. 2540 B Total Solids Dried at 103-105°C. American Public Health Association et al. Washington, DC. Sutherland T.F., P.M. Lane, C.L. Amos, and John Downing. 2000.
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