Installing and connecting a long-term chamber

The 8200-104 Opaque Long-Term Chamber and 8200-104C Clear Long-Term Chamber are used to make continuous measurements of soil gas flux at a single location for weeks or months at a time.

These chambers uses a motor-driven strut system to automatically move the chamber bowl away from the soil collar when not taking a measurement. This ensures that the sample location is subjected to normal, undisturbed precipitation, temperature, and shading between measurements. A patented pressure vent at the top of the chamber prevents pressure spikes when the chamber closes and maintains chamber pressure at ambient levels under calm and windy conditions.

Each chamber has two gaskets: the chamber bowl seals to the base plate with a flexible gasket, and the base plate seals to the soil collar with a second gasket.

Positioning considerations

When installing the 8200-104 Opaque Long-Term Chamber or the 8200-104C Clear Long-Term Chamber it is important to first consider the positioning of the chamber. You will want to ensure there is sufficient clearance for the chamber arm and bowl to swing away. The default open position is 180° from the closed position. See Changing the open position for details on chamber clearance requirements and changing the open position.

You will also want to orient the chamber so that the LI-COR logo stamped on the motor housing faces the equator. This ensures that most of the shadows from the chamber structure are cast away from the collar area to prevent shading effects. This is especially important when making net carbon exchange measurements. See Measuring net carbon exchange for details. Even with this orientation, the collar and chamber may still shade the sample area.

Leveling the chamber

Make sure the soil collar does not shift when placing the chamber on it. The chamber edge should be as close to the soil surface as practical, so that air flow within the chamber causes mixing near the soil surface, while minimizing the amount of the collar that extends into the chamber. Each of the four legs should be adjusted so that the chamber sits evenly over the soil collar.

To adjust a leg, loosen the knob and reposition the leg. Then tighten the knob securely.

Connecting a long-term chamber

Part number:
LI-8250 or 8250-01,
8200-104/C, and 9982-056

The components needed to make this connection are the LI-8250 Multiplexer or 8250-01 Extension Manifold, a long-term chamber (part number 8200-104 or 8200-104C), and the cable assembly (part number 9982-056).

Connecting either the 8200-104 Opaque Long-Term Chamber or the 8200-104C Clear Long-Term Chamber requires the same steps. The multiplexer provides power to the 8200-104/C Long-Term Chambers directly or indirectly via an extension manifold.

The multiplexer, extension manifolds, and long-term chambers all use metal quick-connect fittings for air tubing. A male and female fitting comes factory-installed on the tubing bundle of the 8200-104/C and the cable assembly.

The chambers use a built-in thermistor for a chamber air temperature measurement used in flux calculations. The connector for the thermistor will occupy one of the SENSOR ports on the chamber and is part of the chamber tubing bundle.

First, connect the air tubing quick-connect fittings from the cable assembly to the tubing bundle on the chamber and connect the thermistor to one of the available SENSOR ports. Then, connect the power and communications (RS-422) connector to the PWR/COM port on the housing of the 8200-104/C. The fittings for the thermistor and power and communications are keyed. Be sure to align the key with the slot before tightening until snug. The connection will not fit if the key is not aligned.

Complete the connection by connecting the air tubing quick-connect fittings and the power and communications connector to the port of the chamber connection panel on the LI-8250or 8250-01 Extension Manifold. Ensure that all connections for a long-term chamber are made to the same port number.

Once the RS-422 cable is connected (and if the system is powered on) the OPEN/CLOSE button of the 8200-104/C will illuminate with a green light to indicate it is powered on.

Repeat the steps above for each chamber you need to connect.

Changing the open position

You may program each long-term chamber with one of six open positions ranging from 30° to 180° as shown in Figure 4‑4. The default open position is approximately 180° from the closed position. Five other open positions are available to avoid terrain or obstructions that interfere with the full 180° of movement. Be sure to consider possible shading effects when choosing an open position.

To change the open position:

1. Connect to your LI-8250 Multiplexer and open the user interface.
2. See Connecting to the LI-8250 Multiplexer for instructions on how to connect.
2. Open the Configuration tab and select the chamber by serial number to have the open position changed.
3. Add the Open Position block to the chamber if it is not already present.
4. Select LI-COR Chambers in the Toolbox and find the Open Position block. Then click and drag the Open Position block to the chamber block.
4. Under Open Position of the chamber you can manually enter the new open position into the field in 30° increments, or you may use the mouse over the dial to select the new open position.
5. See Figure 4‑5. The multiplexer will store this setting as the open position for this port until it is changed. If a different chamber is placed on that port, the chamber will use the open position assigned to that port.

Parking the chamber

You can manually change the position of the chamber using the OPEN/CLOSE button on the motor housing. This button has a few different uses but the most common use is to place the chamber into the park position. When in park, the chamber will raise slightly to prevent compressing the chamber gasket. This is the position you will want the long-term chamber in before transporting it, performing maintenance, or storing it.

To place the chamber into park, quickly press the OPEN/CLOSE button twice. If the chamber was open, it will first fully close and then it will raise to the park position.

Below is a complete list of the OPEN/CLOSE button functions.

• A single press will close the chamber if it is open and open the chamber if it is closed.
• Two quick presses will park the chamber.
• Pressing and holding the button will move the chamber slowly in the opposite direction of its last movement.

CAUTION: Be sure to park the chamber before transporting it, performing maintenance, or placing it in long-term storage. Handling the chamber while it is not parked can strain and potentially damage the shaft and sealing mechanism.

Tips for using the 8200-104C Clear Long-Term Chamber

Here are some tips that will help you use the clear long-term chamber.

Shading effects

Shading effects from the structure of the 8200-104C Clear Long-Term Chamber can alter the rate of photosynthesis. To minimize the effect shading has on your results, the 8200-104C should always be oriented so that the LI-COR logo stamped into the motor housing faces the equator. This ensures that most of the shadows from the chamber structure are cast away from the collar area. Even with this orientation, the collar and chamber may still shade the sample area.

Temporal variations in light intensity inside the collar area will occur due strictly to shading from both the chamber and foliage in and around the collar, as the sun moves across the sky. It is important to consider these temporal variations when examining flux data.

Measuring photosynthetically active radiation

When using the clear chamber for net carbon exchange (NCE) measurements, you will want to measure photosynthetically active radiation (PAR) to supplement your measurements. The LI-190R Quantum Sensor can be connected to the 8200-104C Clear Long-Term Chamber to measure PAR at the chamber. This sensor is available in a package (part number 190R-8200) that includes an LI-190R Quantum Sensor and leveling stake to mount and level the sensor.