Each gas has the ability to conduct heat at a specific rate. This is known as the thermal conductivity of the gas. This property is utilized in the Thermco thermal conductivity detector. Heated metal filaments are exposed to the zero and sample gases. The amount of heat carried away by the gas changes the rate of cooling of the wire filament and therefore, its temperature change. This temperature change causes a resistance change. Since the filaments are arranged in a Wheatstone bridge, the resistance change can be converted to an electrical current that is read out on a meter.

Traditionally, a drawback to using the thermal conductivity method has been the non-linear signal created from virtually all-binary gas mixtures. The user had to refer to a curve in order correct for the non-linearity. The model 6900 is a significant improvement in the technology of handling the signal from the thermal conductivity detector. The unique curves generated by the 9 binary gas pairs are each programmed at the factory into the microprocessor in the Model 6900. The user selects the range of interest from the front panel of the *yzer is able to read out directly in the percent gas *ysis for that particular gas mixture.

The calibration stability of the model 6900 *yzer is exceptional, especially compared to the infrared t*e or chemical cell t*e gas *yzers which may require recalibrations on a daily basis. It is recommended that the calibration be checked once per year, if used on a spot checking basis.

CUSTOM RANGE

The user may encounter a gas mixture pair other than the nine standard ranges built into the *yzer. In this case, the user may perform an *ysis by inputting his own calibration data into the *yzer. This can be accomplished by utilizing the push buttons on the front meter. Guidance is available from the factory concerning the thermal conductivity response of a wide variety of gas pairs.

3 GAS MIXTUR*

Although the Model 6900 is not normally intended to measure a 3-part mixture, mixtures of Ar / CO₂/ O₂may be approximately measured if the user knows the oxygen level in the mix. Contact Thermco for details.

SERVICE

Thermco has been providing service for their *yzers since 1951. The Thermco repair department can normally complete repairs in two weeks.

*TICE

The Model 6900 is not intended to measure oxygen/nitrogen mixtures for breathing air, oxygen purity, or other medical applications.

The Model 6900 is not designed to be used with toxic gases or gases corrosive to br* or nylon.

ACC*SORI* SUPPLIED

Along with the *yzer are supplied two 10 ft. lengths of tubing to run from the ports on the Model 6900 to cylinder regulators.

ORDERING INFORMATION

Orders may be placed through many local industrial gas suppliers. Orders may also be placed directly with the Thermco factory.

In the interest of continued product improvement, Thermco reserves the right to change design features without prior notice.

Sale of this equipment is under the terms of the Thermco warranty available on request.