TGA200

Upgrades are now available to operate the TGA200 with a thermoelectrically cooled (TEC) laser, enabling the TGA200 to no longer require liquid nitrogen refills. Upgrading a TGA200 requires a new TEC laser module, TGA200A Input Module, TGA200A Output Module, and TGA TEC software. Contact Campbell Scientific for more information.

The TGA200 Trace-Gas Analyzer measures trace-gas concentration in an air sample using tunable-diode laser absorption spectroscopy (TDLAS). This technique provides high sensitivity, speed, and selectivity. The TGA200 is a rugged, portable instrument designed for use in the field. Common applications include gradient or eddy-covariance flux measurements of methane or nitrous oxide and isotope-ratio measurements of carbon dioxide.

Measurement Specifications

The typical 10-Hz concentration measurement noise is given as the square root of the Allan variance with no averaging (i.e., the two-sample standard deviation). This is comparable to the standard deviation of the 10-Hz samples calculated over a relatively short time (10 s). The typical 30-min average gradient resolution is given as the standard deviation of the difference between two intakes, averaged over 30 min. Values shown in Table OV7.7-1 are for ambient concentrations.

TABLE OV7.1-1. Typical Concentration Measurement Noise

The TGA200 multiple-scan mode can be used to measure suitable pairs of gases. Typical performance for some examples is given in Table OV7.1-2.

TABLE OV7.1-2. Typical Concentration Measurement Noise

Typical performance for isotope ratio measurements is given in delta notation. For example, the δ¹³C for CO₂ is given by:

where R_s is the ratio of the isotopolog concentrations measured by the TGA200 (¹³CO₂/¹²CO₂) and R_VPDB is the standard isotope ratio (¹³C/¹²C). δ¹³C is reported in parts per thousand (per mil or ‰). The 10 Hz noise is the square root of the Allan variance with no averaging. The calibrated noise assumes a typical sampling scenario: two air sample intakes and two calibration samples measured in a 1-minute cycle. It is given as the standard deviation of the calibrated air sample measurements.

TABLE OV7.1-3. Typical Isotope Ratio Measurement Noise