Preparing for measurements

This section describes the how to prepare to take measurements. It assumes you have assembled the system and prepared all of the components as described in Installing the pCO2 system.

Powering on

Press and release the power button to turn on the LI-5405A. A ring around the button illuminates to indicate that the device is powered on. Allow the LI-5405A to warm up for 30 minutes before taking measurements.

Power on the gas analyzer. The LI-7815 will power when power is supplied; if it does not, press the power button. The gas analyzers may take 30 to 45 minutes to warm up depending on the ambient temperature.

Power on the computer. Log in and start the pCO2 application.

Checking the setup

After the initial installation, before opening the water supply or starting measurements, take a moment to check the system.

  • Verify that the equilibrator drain valve is closed (perpendicular to the flow direction).

  • Verify that both blue filter drain valves at the bottom of the water filters are closed (perpendicular to the direction of flow).

  • Verify that both air vents are closed.

  • Verify that the primary and secondary flow valves for the SBE 45 are partially open.

Figure 3‑1. Before opening the main flow valve, be sure the air vents, equilibrator drain valve, both blue filter drain valves are closed. The primary and secondary flow valves for the SBE 45 should be partially open.

Adjusting the water flow rate

Be sure the water supply is connected to the system, capable of providing a range of 2.5 to 5 liters per minute (lpm), with 3.5 liters per minute (lpm) ideally and 60 pounds per square inch (4.14 bar).

  1. Open the intake valve until water is evenly and gently sprayed in the equilibrators.

    Open is parallel to the direction of flow; closed is perpendicular. Water will flood the system, flow through the equilibrators, and exit from the discharge tube.

    • Pressure too low: Water is dripping or flowing as large drops, a single stream, or a few streams.
    • Pressure too high: Water is sprayed forcefully against the sides of the equilibrator.
    • Pressure just right: Water is sprayed evenly and gently. Some flows down the inside of the equilibrator after forming small droplets.

    If you see a water leak, take a moment to fix it now. Tighten loose fittings or press tubing into quick-connect fittings.

  2. Test flow through both filters.

    Switch both filter valves simultaneously to flood the other filter. Be sure neither of the filters leak.

  3. Adjust the SBE 45 primary flow valve until the meter indicates 20 gallons per hour (76 liters per hour).

    The flow rate range should be between 10 to 28 gallons per hour (38 to 106 liters per hour).

  4. Adjust the secondary flow valve to achieve an ideal flow pattern in the equilibrator.

    Continue to adjust both valves until both the flow pattern and flow rate are both ideal.

Caution: The water sample flowing through the equilibrator must be discharged freely under gravity. If the discharge pipe is clogged, the measurements may be inaccurate and equipment may be damaged. Be sure the discharge pipe is set properly.

Initial configuration

Launch the Underway PCO2.exe program and allow it to initialize. You'll be presented with options to connect to components and configure measurements. Some options are no longer supported, as indicated.

Note: If the interface does not fit on the screen, adjust the display settings. Press the Windows key (), type display, and press Enter. In Display settings, change Scale and Layout to either 125% or 100%.

  1. Select the sensors that are part of the system.

    Click In Use or Not In Use for each sensor that is part of your system.

    • GPS and Honeywell Durafet - pH are no longer supported and should be Not In Use.
    • Aanderaa Dissolved Oxygen, Cyclops Chlorophyll and Weather Station should be set to In Use if these components are part of your system.

  2. Configure the devices - click Device Config..

    Configure settings for the gas analyzer, GPS source, overflow alarm criteria, chlorophyll sensor calibration, and peristaltic pump.

    • LI-COR Model: Select the gas analyzer model from the list. Currently, only LI-7815 is supported. Select the model and then enter the Hostname (on the serial number label). Click Set to apply the changes.
    • GPS Input: Leave these at the default settings. GPS data are provided by the Airmar Weather Station. Other GPS sources are not supported.
    • Overflow Alarm: Criteria to trigger an alarm and abort a measurement. Choose 1X or 2X to set the number of times the overflow events happen before triggering the alarm, and set the time to wait between overflow triggers.
    • Chlorophyll Sensor: The default coefficients are fine for many applications. Later, in Experiment Setup, you can choose the gain setting for the sensor. You can also improve the performance of the sensor with a manual calibration, if desired (see User calibration). Click Set to apply changes.
    • Peristaltic Pump: Peristaltic pumps evacuate water from the condenser. The default settings will work for many situations, but you can make adjustments. Interval (mins) is the time that the pumps are off. Pump ON (mins) is the time that the pumps run between idle periods. The pumps always run after the measurement is initiated (by clicking Start Sample) and the Interval timer starts at that time. Click Save to apply the changes.

  3. Save the settings - click System Init. in the upper left to save the settings.

  4. Click Connect to establish communication between the device and program.

    The interface will display the status of each device. If you observe a failed status, check communication cables, power supplies for powered components, and make sure the gas analyzer is powered on.

If everything checks out, you are ready to collect data. Proceed to Measuring pCO2 in water.