Attaching gas analyzers

The LI-8250 Multiplexer is compatible with LI-COR gas analyzers, gas analyzers from other manufacturers, and multiple analyzers at once. For LI-COR gas analyzers you'll connect tubing and cables between the gas analyzer and multiplexer.

LI-870 cables and tubes

The LI-870 connects to the multiplexer with cable assembly 9982-010. This bundle includes two pieces of tubing, a power cable, and a USB data cable. The LI-870 is powered directly from the LI-8250 Multiplexer.

Caution: The LI-870 CO2/H2O Analyzer is water-resistant, but it is not waterproof. It should not be allowed to sit in standing water or be directly exposed to driving rain. In hot environments, the LI-870 CO2/H2O Analyzer may require a cover for shade to stay within its operating temperature range (-20 to 45 °C, without solar loading).

The LI-8250 Multiplexer and the LI-870 CO2/H2O Analyzer both use quick-connect fittings for air tubes.

  1. Connect the cables and tubes to the LI-870.

    The power cable has a knurled connector; tighten it until snug. The USB cable has clips on the top and bottom; be sure both clips are locked to the connector. The tubes have quick-connect fittings that attach to the compatible port.

  2. Connect the cables and tubes to the LI-8250.

    Tighten the power cable connector until snug. Be sure both clips on the USB cable are locked to the connector. Tubes connect directly to the compatible AIR IN and AIR OUT ports on the LI-8250.

Note: Only use the supplied USB cable from the LI-870 cable assembly.

The LI-870 is powered by the LI-8250 Multiplexer. It will power on when the LI-8250 is powered on. Allow the LI-870 to warm up for 10 to 15 minutes before making measurements, or longer if starting from a very cold temperature.

LI-78xx Trace Gas Analyzer cables and tubes

This section describes how to connect tubing and data cables between the LI-78xx Trace Gas Analyzer to the LI-8250 Multiplexer.

LI-78xx Trace Gas Analyzers connect to the multiplexer with 9982-011 cable/tube bundle. This bundle includes a weather-resistant network cable and tubing for gases.

Note: Only use the supplied Ethernet cable from the LI-78xx Trace Gas Analyzer cable assembly (part number 9982-011).

  1. Connect tubes to the LI-78xx Trace Gas Analyzer.

    The tube that is wrapped in black shrink wrap connects to the IN port of trace gas analyzer; the other tube connects to the OUT port. Tubes connect with compression fittings. The nut (300-05896), along with a steel insert (300-18126), bushing, and ferrule (300-15024) are installed on one end of the tube.

    A gas analyzer inlet and outlet accepts tubing with ferrules, bushings, and a nut that must be tightened.

  2. For both tubes, thread the nut onto the gas analyzer fitting until finger tight and tighten the nut an additional ¼ turn with a wrench to seal the fitting.

  3. Connect the network cable to the network port on the Trace Gas Analyzer.

  4. On the other end of the cable/tube bundle, connect the quick-connect fittings to the AIR IN and AIR OUT ports on the LI-8250.

  5. Connect network cable to the LI-8250

    Any available network port will work. Be sure that both clips on the network connector are locked on the connector.

Caution: LI-78xx Trace Gas Analyzers are water-resistant, but they are not waterproof. They should not be allowed to sit in standing water, be directly exposed to driving rain, or be deployed outdoors without weather protection.

Connecting multiple gas analyzers

The LI-8250 Multiplexer can simultaneously connect to both an LI-870 CO2/H2O Analyzer and an LI-78xx Trace Gas Analyzer or multiple Trace Gas Analyzers with the T-split tubing (part number 9982-073). The power and communications connections are the same as those used in LI-870 cables and tubes and LI-78xx Trace Gas Analyzer cables and tubes. If you are using three Trace Gas Analyzers, the tubing configuration is described in Attaching gas analyzers with the calibration manifold.

Figure 2‑2. The LI-870 and one Trace Gas Analyzer are connected using the tube t-split.
Figure 2‑3. Two Trace Gas Analyzers are connected using the tube t-split.

Connect the long leg to the respective IN or OUT port on the LI-8250 Multiplexer. Then connect the short legs (8 cm) to the respective ends of the analyzer LI-870 and LI-78xx cable assemblies. If you are using three Trace Gas Analyzers, the tubing configuration is described in Attaching gas analyzers with the calibration manifold.

Each "leg" of a T-split tubing will add 15 cm of tubing length to the total tubing for one gas analyzer.