Operational Theory 2.0 - Teledyne 514 Instruction Manual

2.0 Operational Theory
The energy source for the analyzer is provided by a high intensity
quartz iodine lamp located in the source module. Quartz iodine was chosen
because it produces sufficient NIR to operate the system and maintains a
nearly constant brightness over its lifetime. (See Figures 2-1 and 2-2).
This energy is then fed through the sample, which is temperature
controlled, and into the detector module where it passes through a rotating
filter wheel before reaching the lead sulfide (PbS) detector.
The filter wheel, driven at 30 RPS or 1800 RPM by a synchronous
AC motor, contains two optical filters with bandpasses selected for each
application, thus providing reference and measuring pulses from which the
required information may be obtained.
The detector receives pulses at the rate of 60 PPS, or two pulses per
revolution of the filter wheel. Every other pulse is from the measuring
filter, while the alternate pulse is from the reference filter, so that pulses
through the measuring filter alternate with pulses through the reference
filter. A filter position sensor, which is an optical device having an integral
light source and light detector, differentiates between the two.
The two entrained pulses received by the detector each revolution are
amplified through a preamplifier which is physically located inside the
sealed compartment with the filter wheel and detector. This signal is then
sent to a clamping circuit where an exact zero reference is established.
This clamped video signal is then fed through a gain control network,
which is controlled by the automatic gain control loop, through another
amplifier, to the electronic switch. This switch is controlled by the switch
driver network which derives its information from the filter position sensor
in order to separate the entrained video signal into its component parts of a
measuring peak and a reference peak. These peaks are then fed through a
balancing network and channeled into separate peak height detectors which
produce DC voltage levels which are exactly equal to the peak height or
absolute magnitude of the voltage from the base to the peak of each of the
pulses.
Teledyne Analytical Instruments
A Business Unit of Teledyne Electronic Technologies

Operational Theory 2.0

2–1