Teledyne 514 - NDIR analyzer - Manual (Page 15)

2–3
Operational Theory 2.0
Teledyne Analytical Instruments
A Business Unit of Teledyne Electronic Technologies
losses in the sample module due to strong sample absorbance or exception-
ally long sample path-lengths. These systems require a focusing lens to
gather and collimate the radiation for maximum utilization of source
energy. The collimating lens is quartz.
Figure 2-1. Optical System
2.1.2 Sample Module
The sample cell, generally constructed of 316SS, is located in the path
of the NIR radiation, between the source and the detector modules. Each
compound in the sample path exhibits its own characteristic absorption
spectrum. Cell spacer thicknesses will vary depending upon the absorbance
of the component of interest at the measuring wavelength. Due to the
possible variation of absorption with temperature, it is necessary to main-
tain the sample at a constant temperature during analysis. To achieve this,
two separate methods of temperature control are employed
1. A preheater is used on the incoming sample stream to raise it to
the desired level.
2. The entire sample module is separately controlled to maintain
the sample temperature during analysis.