Calibrating the Probes
Calibration of the probes:
To calibrate the probes, a two point method is used. The computer or calculator takes two voltage readings to which a specific, set value is assigned.
Calibration using the LabPro and a Graphing Calculator:
Turn on the calculator and go to the DataMate Program using the APPS button. Select the DataMate Program. Connect the nitrate, ammonium, calcium, and dissolved oxygen probes to the side of the LabPro in the four available channels. The calculator should read "Checking Sensors". The next screen should list each of the sensors in proper order, except for the dissolved oxygen probe. You will have to identify the dissolved oxygen probe for the calculator by selecting "Setup" from the menu. On the next screen, select channel four, where the dissolved oxygen probe is connected, and press the Enter button. There should be a list of various probes from which to select Dissolved Oxygen. Now the program has recognized each of the probes.
Calibrating the ISE Probes:
Go back to the previous screen (the "setup" screen) and select one of the probes to calibrate, then select the command "calibration." From the next screen, select "calibrate now" . Leave the probe soaking in the High Standard for the first point selection. The calculator will take a voltage reading of the standard solution. When this reading stabilizes, press Enter. The next screen will prompt you to enter the value for that point. For the first point, enter the value of the high standard solution,located on the bottle, for that particular probe . Remove the probe from the soaking bottle and empty the high standard solution. Rinse the bottle with distilled water, pour this water out, and fill the bottle three-quarters full with the low standard solution for that particular probe. Press Enter again and the calculator will immediately begin taking the second voltage reading. When this reading stabilizes press Enter and then enter the valuefor the low standard solution, located on the low standard solution bottle. Press Enter . This will return to the calibration menu. From this screen, select "OK." This will return to the setup menu. Now select the next probe to be calibrated. Repeat this calibration procedure for each of the ISE probes (Nitrate, Ammonium, Calcium.)
If you are going to the field to take measurements immediately after calibration, store the calibrated probe in its empty "short term storage" bottle. If you are not going to take measurements in the field immediately after calibration, store the calibrated probe in its high standard solution until measurements will be taken. However, the probes cannot soak for longer than twenty-four hours in either of the standard solutions.
Calibrating the Dissolved Oxygen Probe:
If the probe is still in the 75 ml of distilled water, remove the probe from the water. On the calculator, select the dissolved oxygen probe from the "setup" menu and then select "calibration," and then "calibrate now." For the first calibration point used, use the sodium sulfite calibration solution. This solution keeps oxygen from dissolving in it (if it is stored properly, brim-full) and so can be used as a zero calibration point. When the voltage reading stabilizes, press Enter and then the number zero. Remove the probe and prepare the standard solution for storage. The standard solution for the dissolved oxygen probe must be carefully stored. Squeeze the bottle so that the liqiud is even with the top of the bottle, and while still squeezing, screw the top on to the bottle. This is necessary to keep from trapping any air in the sealed bottle, which would then contribute oxygen molecules to dissolve in the solution, changing the standard value.
Locate the small plastic bottle for use with the dissolved oxygen probe. Fill the bottle about 1/4 of an inch full of water. If it is not already attatched, slide the lid and grommet onto the probe. Without allowing the probe to get wet, screw the lid and probe on the bottle keeping the probe above the water level. If you have not already done so, press Enter which will immediately begin the next voltage reading. When this stabilizes, press Enter and enter a saturated dissolved oxygen value. To calculate this value, use "Table 1" on page five of the vernier manual for the dissolved oxygen probe. This table assists in extracting the dissolved oxygen value at the present air temperature and barometric pressure. After calculating this number, enter it in the calculator and press Enter. Follow the commands to take you back to the "setup" screen.
After performing the calibrations for each of the probes, you will need to save these numbers in a program on the calculator. From the "setup" screen, select "save/load experiment." Select "save" from the following screen. The calculator will prompt you to name the experiment. Save the experiment as the date of collection. Press Enter and return to the setup screen.
Disconnect the probes from the LabPro, and connect the conductivity and flow rate probes. The calculator should indicate that it is checking sensors, and should recognize both of these probes.
Calibration of the Conductivity Probe:
Go to the calibration screen, as performed earlier with the other probes, and select "calibrate now" and perform the zero calibration point. Hold the probe in the air, out of any solution, and when the voltage reading stabilizes, press Enter and enter the number zero. Press Enter again and place the probe in the sodium chloride standard solution. When the voltage reading stabilizes, press Enter and enter the value of the standard solution (located on the label of the bottle) and press Enter again. Follow the commands to get back to the "setup" screen again.
Calibration of the Flow Rate Probe:
This sensor does not need to be calibrated.
As before, you will need to save the calibration performed for the conductivity probe. Follow the commands from the earlier section and name the experiment as the date of collection, part B.
Calibration of the pH Probe:
Locate the pre-mixed standard pH solutions with a pH of 7 and 4. Attatch the pH probe to the Oyster pH Meter, place the probe in the pH 7 solution and turn the meter on. Allow the probe to remain in the solution for two minutes or until the meter stabilizes. Once the value has stabilized, adjust the "CALIB" dial (on the right of the meter) until the display value is 7.00. Remove the probe from this solution and rinse it with distilled water. Now place the probe in the standard solution of pH 4. Allow the probe to remain in the solution for two minutes or until the value stabilizes. Now use the "SLOPE" dial (on the left of the meter) to adjust the value on the screen until it reads 4, which is the value of the pH of the solution it is in. Turn the pH meter off, rinse the probe with distilled water and store the probe in its protective bottle.
Now you are ready to take measurements in the field. Before leaving,
make sure you have all six probes: Nitrate, Ammonium, Calcium, Dissolved
Oxygen, Conductivity, and Flow Rate. Be sure to take a thermometer, something
to measure pH, a data collection sheet, and something to write with.
Developed by Emily Blackwell with assistance from Dr. Mark Lassiter
This procedure is a modified version of the procedures for
:
| Vernier LabPro Probes | Extech Economy Oyster pH Meter Kit |
| Vernier Software & Technology | Extech Instruments Corporation |
| 13979 S.W. Millikan Way | 335 Bear Hill Road |
| Beaverton, OR 97005-2886 | Waltham, MA 02154 |
| www.vernier.com | Fax: (617) 890-7864 |
Site prepared by Mark Lassiter, 1/23/2002