Match Valve Mismatch

With the LI-6400XT Portable Photosynthesis System

Printable PDF: Match Valve Mismatch

Tech tip for checking the position of the match valve.

The match valve in the LI-6400XT Portable Photosynthesis System is one of the most important but also one of the most overlooked components. Using the match valve allows you to flow the same air stream through the reference and sample analyzers. When the same air flows through both analyzers, the LI-6400XT software can account for minor offsets which could affect the data. It is important to match before the first measurement of the day and periodically throughout the day, especially when there is a large change in CO2 concentration, temperature, or flow rate, or if it has been more than 30 minutes since the last match. If the match valve isn’t working, there will be no (or wrong) corrections for minor analyzer offsets, which may mean increasing errors in your data as the measurement progresses.

How can you know if your match valve is properly installed and working correctly? It’s simple; the picture below shows the match valve’s proper orientation when match mode is OFF.

Figure 1‑1. The match valve appears in this orientation when in the Off position.

When you are in Match Mode (menu level 1, key f5) and the match valve is ON, the match valve should be in the opposite orientation, as shown below:

Figure 1‑2. The match valve appears in this orientation when in the On position.

If the match valve does not move when entering match mode, there may be a pinched wire or another problem with the valve. Follow the tips in the Match Valve Maintenance section of Chapter 19 of the LI-6400XT instruction manual to free the valve or otherwise determine the problem. If you are unable to determine what’s wrong or solve the issue, please contact our technical support team at 800-447-3576 or 402-467-3576, or email