Installing the pCO2 system

The pCO2 system should be installed on a bench in a protected area on a ship or lab, close to a dependable power supply. The room should have adequate ventilation and remain near room temperature (25 °C) with relative humidity below 85%. The system needs a water supply (around 3.5 liters per minute (lpm) with 60 pounds per square inch (4.14 bar) pressure) and a drain for water after measurement.

Warning: The components of this product are heavy. Use caution to avoid injury when lifting and securing components. Moving the fully assembled product should not be undertaken without appropriate precautions (e.g., a mechanical lift system, two-person lift, or other suitable lifting method). See Specifications for weights.

Figure 2‑1. When deployed, the pCO2 system will be connected to gas standards (3 to 5) and the LI-7815 Trace Gas Analyzer. The pCO2 system connects to a computer with a USB cable. The gas analyzer connects to the computer with a network cable. The Airmar weather station connects with a serial cable. The ambient air intake should be open to ambient air and protected to prevent water from entering the tube.

Connecting data cables

The pCO2 system connects to the computer with a USB cable. The LI-7815 connects to the computer with a network cable (RJ-45). Connect the Airmar Weather Station data cable to the serial port on the right side of the pCO2 system. Configuration information is provided in Initial configuration. For the final installation of the weather station, be sure it is in an open area with a clear view of the sky away from elements that can interfere with wind measurements.

The LI-7815 attaches to the computer with a network cable. The LI-850 attaches with the USB cable.
Figure 2‑2. The computer controls the pCO2 system. It also logs data from the pCO2 system and measurements from the gas analyzer and weather station.

Connecting the power supply

The pCO2 system requires either 110 VAC at 60 Hz or 220 VAC at 50 Hz. Be sure the device is compatible with the power source before connecting the power cable. Both the computer and gas analyzer can be powered by 110 to 220 VAC, 60 or 50 Hz. They can be connected to a power supply with the included power adapters. The LI-7815 includes two rechargable batteries, which can be installed in the gas analyzer so it continues running if the main power supply is disrupted. A surge protector may be used to protect the instrument. An uninterruptible power supply (UPS) may be used to prevent unexpected power disruptions.

Warning: An earth ground is required to reduce the risk of electric shock. Do not disable the earth ground. Failure to use an earth ground presents the risk of injury or death

Caution: Be sure that the instrument is compatible with the power supply. Connecting to an incompatible power supply may damage equipment or cause injury.

After connecting power cables, you can power everything on. The gas analyzer should be allowed to warm up for about one hour before taking measurements.

Attaching gas standards

Gas connections are made with tubing to the connections on the side of the pCO2 system. Gases should be connected to the pCO2 system with 1/8" OD copper or stainless steel tubes. Each tank should be equipped with a two-stage regulator. An additional low pressure regulator may be needed if the pressure is too high.

Warning: Compressed gas cylinders present hazards. Safe handling is critical for your safety and the safety of others. Risks of an unsafe deployment include explosion, suffocation, or crush hazards. Be sure to understand and comply with local laws regarding compressed gas cylinders. If you work for an academic or governmental organization, additional safety rules may apply.

These recommendations are offered for general safety, but are not authoritative or complete. You are responsible for your own safety and the safety of others who are working with or nearby your equipment. If you do not understand how to use a gas cylinder in a safe manner, defer to someone who does or get professional training. Be mindful of the following recommendations:

  • Gas cylinders must be installed in a vertical position. Do not lay them over.
  • Gas cylinders must be secured in accordance with local laws. A permanent structure may be required.
  • Gas cylinders should not be exposed to heat in excess of the specifications on the tank.
  • Gas cylinders should be stored in a well-ventilated area.
  • Enclose the cylinders in a locked cage or shed to prevent access by unauthorized people and other animals.
  • Additional security may be required if cylinders are deployed in a public area.

Connect 1/8" OD stainless steel or copper tubing to the CO2 standard ports on the right side of the system. Three gas standards are adequate; up to five can be used.

Figure 2‑3. Gas standards connect to panel connectors 1 to 5 with copper or stainless steel tubing. A ferrule, bushing, and nut are used to secure tubing to the connectors on the gases panel. A coil in the tubing can allow for flexibility to relieve strain.

Tighten the nut to finger tight and then, while holding the fitting body with a wrench, tighten the nut another 3/4 turn. For 1/8" tube fittings, wrench sizes are 1/2" for the body and 7/16" for the nut.

After connecting all reference gases to the system, you can adjust the two-stage regulators to a delivery pressure of 15 psi (1 atm), pressurize the system, and make sure there are no gas leaks. When not taking measurements, close the valves on the tanks to prevent loss of the gases.

Attaching the ambient air supply

Use 1/4" OD gas-tight tubing for the ambient air intake. For ship-borne measurements, the inlet of the atmospheric tube should be on or near the highest point on the bow of the ship to avoid sampling exhaust gases or eddies created by the ship. In order to avoid possible contamination from the ship exhaust gases, atmospheric CO2 data should be used only when the ship is moving and the wind is blowing from the bow. To keep water from entering the inlet, cover the inlet with an upside-down bottle or a rain/splash shield. To tighten the 1/4" tube fittings, use 5/8" and 9/16" wrenches. Hold the fitting with one wrench while you tighten the nut with the other wrench.

One tube provides amibient air to the system.
Figure 2‑4. The ambient air intake connects to the Air In connection.

Attaching gas analyzer tubing

Use two pieces of 1/4" OD Bev-a-line® tubing - each about 1 meter long - to connect the gas analyzer air inlet with the LI-5405A. One tube connects TO ANALYZER from the pCO2 system to air IN on the gas analyzer. The other tube connects FROM ANALYZER to air OUT on the analyzer (see Figure 2‑5). Tighten each nut to finger tight, and then an additional 1/4 turn with a wrench.

Figure 2‑5. The trace gas analyzer connects to the pCO2 system with 1/4" Bev-a-line tubing. Use plastic ferrules with plastic tubing.
Figure 2‑6. The gas analyzer can be set on top of the pCO2 system with the display and handle facing forward for easy access. It can be secured to the top with the two brackets.

Attaching the sample water supply

The sample water supply connector is on the front of the system. Remove the cap from the intake.

A water pump with a flow rate between 2.5 to 5 liters per minute (lpm) (ideally 3.5 liters per minute (lpm)) at 60 pounds per square inch (4.14 bar) should be used to supply sample water to the pCO2 system.

Many research vessels have a water sample pump that can be used to supply water if the flow rate and the pressure meet the criteria. A pressure regulator may be used to prevent variations in water supply when the source water is shared with other devices in the ship. The water pump needs to shut off or split before the water inlet to relieve pressure when the shut-off valve in the pCO2 system in engaged.

Install the yellow connector on the water inlet. Tighten no more than four full turns when connecting it to the system. After four turns, it may feel that it still could be tightened, but stop here and do not overtighten it. Over-tightening will compromise the O-ring and may cause leaks.

Attaching the waste water discharge tubes

Remove the cap. A piece of 3/4" pipe or soft hose is used for water discharge. Water flows through the equilibrator inside the system and is discharged by gravity. Allow the outlet of the equilibrator to drain into a sink or floor drain. If a tube or a pipe is attached to the outlet, ensure it is not pinched or restricted in any way.

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.