LI-840 Description

Sophisticated Technology

The LI-840 is an absolute, non-dispersive, infrared (NDIR) gas analyzer based on a single, interchangeable optical path, and a dual wavelength infrared detection system.  It includes a 14 cm optical path coupled by the source and detector.  Air enters through the inlet port (a pump is needed), passes through the optical path and exits through the outlet port.

A built-in pressure sensor and thermostatically controlled optical bench provide excellent stability over time and pressure changes.  This reduces the need for frequent zero and span adjustments.

User-defined 0-5 V high and low alarm relay outputs allows control of CO₂ and/or H₂O within a desired range.  For example, the analyzer can be configured to trigger exhaust fans in a greenhouse to vent excess CO₂ or H₂O.  These relays can also trigger devices such as automatic dialers, audible alarms, pumps, or valves in industrial applications.  Activated alarms are also indicated by LEDs on the instrument top panels.

Making Measurements

The LI-840 is a very simple gas analyzer to use.  A pump is connected to the inlet port so that air passes through the optical path and exits through the outlet port.  You have four choices for data output (see Software and Data Output section). 

The LI-840 optical path is a thermostatically controlled IR detection system that provides excellent stability over both time and temperature, which extends the required interval for calibration. Integrated thermistors and a pressure transducer provide for high accuracy in the concentration calculation over the entire measurement range.

The optical path of the LI-840 features:

• Gold-plated reflectors and optical paths that increase energy transmission

• Narrow band optical filters that allow simultaneous measurement of CO₂ or H₂O in a single path

• Optical path is in direct contact with source and detector housing to achieve thermal equilibrium

• Pressure transducer within the gas flow path to minimize variability due to changes in barometric pressure

• A foam enclosure surrounding the optical path to maintain a controlled thermal environment and protect the bench from mechanical shock and vibration

The LI-840 is powered by 12-30 VDC input voltage.  Batteries or AC power (requires AC adapter) can be used to power the instrument.  Low power consumption (~ 0.3 A @ 12 V average after warm-up) makes the LI-840 suitable for a wide range of applications where power is limited.