Teledyne GAS Filter Correlation, Absorption Path Lengths for GFC 7001E and GFC 7001EM

Theory of Operation Model GFC7001E Carbon Dioxide Analyzer

Lengthening the absorption path is accomplished partly by making the physical dimension of the reaction cell longer, but primarily by adding extra passes back and forth along the length of the chamber.

Table 11-1: Absorption Path Lengths for GFC 7001E and GFC 7001EM

MODEL	TOTAL NUMBER OF	DISTANCE BETWEEN MIRRORS	TOTAL
			ABSORPTION LIGHT
	REFLECTIVE PASSES
			PATH
GFC 7001E	32	437.5 mm	14 Meters
GFC 7001EM	8	312.5 mm	2.5 Meters

IR

Source

Band-Pass Filter

Sample Chamber

Photo-Detector

IR Beam

Figure 11-1: Measurement Fundamentals

Upon exiting the sample cell, the beam shines through a band-pass filter that allows only light at a wavelength of

4.7µm to pass. Finally, the beam strikes a solid-state photo-detector that converts the light signal into a modulated voltage signal representing the attenuated intensity of the beam.

11.2.1.GAS FILTER CORRELATION

Unfortunately, water vapor absorbs light at 4.7 µm too. To overcome the interfering effects of water vapor the GFC 7001E/EM adds another component to the IR light path called a Gas Filter Correlation (GFC) Wheel.

Measurement Cell

(Pure N2)

Reference Cell

(N2 with CO)

Figure 11-2: GFC Wheel

Teledyne Analytical Instruments 230