Teledyne gfc 7000ta operation manual Optical Bench & GFC Wheel, Temperature Control, IR Source

Theory of Operation Model GFC7000TA Carbon Dioxide Analyzer

9.3.3. Optical Bench & GFC Wheel

Electronically, the Model GFC 7000TA’s optical bench, GFC wheel and associated components do more than simply measure the amount of CO2 present in the sample chamber. A variety of other critical functions are performed here as well.

9.3.3.1. Temperature Control

Because the temperature of a gas affects its density and therefore the amount of light absorbed by that gas it is important to reduce the effect of fluctuations in ambient temperature on the Model GFC 7000TA’s measurement of CO2. To accomplish this the temperature of both the sample chamber and the GFC Wheel are maintained at constant temperatures above their normal operating ranges.

Bench Temperature: To minimize the effects of ambient temperature variations on the sample measurement, the sample chamber is heated to 48°C (8 degrees above the maximum suggested ambient operating temperature for the analyzer). The heat source is a strip heater attached to the underside of the chamber housing. The temperature of the sample chamber is sensed by a thermistor attached to the sample chamber housing.

Wheel Temperature: To minimize the effects of temperature variations caused by the near proximity of the IR Source to the GFC wheel on the gases contained in the wheel, it is also raised to a high temperature level. Because the IR Source itself is very hot, the set point for this heat circuit is 68°C. The heat source is a cartridge heater implanted into the heat sync on the motor. The temperature of the wheel/motor assembly is sensed by a thermistor inserted into the heat sync.

Both heaters operate off of the AC line voltage supplied to the instrument.

9.3.3.2. IR Source

The light used to detect CO2 in the sample chamber is generated by an element heated to approximately 1100oC producing infrared radiation across a broad band. This radiation is optically filtered after it has passed through the GFC Wheel and the sample chamber and just before it reaches the photo-detector to eliminate all black body radiation and other extraneous IR emitted by the various components of those components.

Teledyne Analytical Instruments 200