Using the LI-870

The basic operation of the LI-870 involves connecting the USB data cable, connecting the tubing, and connecting the power cable between the LI-870 and Smart Chamber or LI-8250 Multiplexer, as described here.

Connecting the cable assembly

Connecting the LI-870 to the Smart Chamber or LI-8250 Multiplexer is simple, only requiring a few steps.

First, attach each end of the cable assembly to the LI-870. The USB-B end of the USB-A to USB-B cable is attached to the LI-870, while the USB-A end is attached to the Smart Chamber or LI-8250.

Note: Only use the supplied USB-A to USB-B cable from the LI-870 to cable assembly (part number 9982-010).

Next, attach the cable assembly to the Smart Chamber or LI-8250. Connect the steel quick connect fittings for the air tubing, and thread the power cable on to the power-in and power-out connectors on each panel. Tighten snugly to ensure a water-tight seal. Follow the detailed instructions in the Smart Chamber or LI-8250 instruction manual for additional details.

Warning: The power output is 10-17 VDC with a center positive pin . The output has a 2 amp maximum and is designed to only power the LI-870 CO2/H2O Analyzer Accessory. Only use the power cable supplied with the LI-870 cable assembly (P/N 9982-010), and do not attempt to power any other devices with the Smart Chamber or LI-8250. Drawing a current in excess of 2 amps will trip the self-resetting breaker. If you trip the self-resetting breaker, you will need to wait for a few minutes before attempting to re-power the LI-870.

Powering the analyzer and making measurements

After connecting the power cable, you should power on your Smart Chamber or LI-8250 and launch the user interface software. Power to the LI-870 is supplied directly from the Smart Chamber or LI-8250.

Identifying the LI-870 serial number

In the Settings page of the Smart Chamber or LI-8250 interface, you will need to connect to your LI-870 using the serial number. The label is on the bottom of the case.

Warm up time

The LI-870 will boot up as soon as power is supplied from the chamber. The optical bench should be allowed to warm up prior to taking measurements. The LI-870 optical bench is temperature- and pressure-controlled, so a sudden influx of ambient air into an optical bench that has not been allowed to warm up and stabilize will likely produce noisy data. For this reason, it is critical that your analyzer is allowed to warm up prior to taking measurements. In most cases, 10 to 15 minutes of warm up time will allow the optical bench to stabilize, but warmup time depends largely on ambient temperature.

In the Smart Chamber and LI-8250 interface, you can see when your LI-870 optical bench has stabilized when the dot in the upper-left portion of any screen by the time stamp is green. If the bench is not stabilized, this dot will be red.

You can also visualize the optical bench temperature and pressure from the Home Page of the Smart Chamber or LI-8250 interface to assess whether they have stabilized. After connecting to the Smart Chamber or LI-8250, from the Home Page, select Click to Set. In the Select a variable... window that opens, open the LI-870 list, and you can select Cell Temperature and Cell Pressure.

These variables will now be in the grid on the Home Page. Click them again to graph the values live.

The axes auto-scale, so pay close attention to the axis labels to assess stability. In the example graph above, the bench temperature, for example, is stabilized within roughly ± 0.1 °C from the median value/middle of the graph. Once the values have stabilized like this, you can begin taking measurements following the instructions in the Smart Chamber or LI-8250 manual.

Storing the LI-870

The post-purge function of the Smart Chamber is designed to allow for ambient air to flush CO2- and water vapor-rich air from the cable assembly tubing and analyzer after each measurement. When you are performing your last measurement(s) of the season, or when you return to the lab or desk after taking your last measurements, you should perform a measurement or two with the Smart Chamber to allow dry ambient air to flow through your chamber. This will help to remove humidity before storage.

Note: For more information on post-purge, consult the Smart Chamber manual or find resources online at licor.com/env/support.

The LI-870 should be stored in non-condensing conditions. If the instrument is stored in high humidity or moderate humidity for a long time while powered off, some optical components may temporarily become saturated with humidity. If this occurs, the instrument may need to run for several days before readings return to normal. If possible, store the instrument in an air conditioned environment.