LI-COR LI-7820, Instruction Manual

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Important: Abrupt pressure transients up to 35 kPa above ambient pressure may
cause momentary status warnings and measurement inaccuracies. Longer lasting
pressure excursions may cause the instrument to reinitialize measurement con-
trol loops. The instrument will always record the status associated with a data
value. Under high pressures, the pressure relief valve may open temporarily until
the pressure returns to an acceptable level. Pressures in excess of 110 kPa abso-
lute pressure may damage the instrument.
Plumbing a subsample
Note: We are currently refining numerous sampling protocols for the LI-7820.
Contact LI-COR technical support (envsupport@licor.com) if you have questions
about your application.
A typical sampling application will use the LI-7820 to subsample a gas from a main
sample line. Air passes a single time through the gas analyzer before it is dis-
charged. Air supplied to the sample inlet should be between ambient and 35 kPa (5
PSI) above ambient. If the pressure is higher than that, install a 30 cm vent in the
sample line to ensure that air from the external pump does not pressurize the ana-
lyzer. The vent must be sufficiently long to prevent diffusion of ambient air into
the sample air supply.
Figure 3-3. A basic open system, where air is supplied to the gas analyzer by an external
pump. If the pressure exceeds 35 kPa above ambient, install a 30 cm vent in the air supply
line. Attach the inlet to the 'leg' of the T-fitting to avoid isotopic fractioning.
Section 3. Applications of the LI-7820
3-3 Plumbing a subsample