Circuit Description; Source Module - Teledyne 514 Instruction Manual

2.0 Operational Theory
At this point the reference signal is fed back to the automatic gain
control loop to maintain the desired system gain. In addition, both the
measuring and reference levels are fed to selector switches in order to
enable direct meter indication, which greatly eases the task of balancing
the system during initial system installation and periods of calibration.
The DC voltage levels are fed to a logarithmic ratio amplifier which
produces a voltage output that is proportional to the logarithm of the ratio
of the two DC input voltages. This output voltage, directly proportional to
the concentration of sample, is, within certain limits, a linear function of
the concentration. For purposes of transmission, the voltage signal is
converted by an E-to-I converter; thus, the output signal from the analysis
unit is a current signal that is proportional to the concentration of sample in
the sample module.
Upon arrival at the control module, which is normally located in a
remote location away from the analyzer unit, the signal is processed
through an I-to-E converter which incorporates fine zero and span controls
for calibration. Following the span control, a buffer amplifier provides
isolation between the calibrated signal and any of the selected output
devices. This signal is then sent to the meter driver circuit and readout
meter, to the alarm comparator circuits, voltage output circuits, current
output circuits, etc., depending upon the particular application requirement.
There is also an option of providing an automatic zero circuit (see
drawing B-14729) in the control unit. This circuit provides electrical
signals for switching a fluid which contains none of the material to be
measured into the sample module, electrically adjusting the zeros and
switching back to sample.
2.1

2.1.1 Source Module

The source module is the source of infrared energy. This is provided
through the use of a high-intensity quartz iodine lamp operating directly
from a 6.3 V transformer. To ensure a stable source of radiation in the face
of line-voltage variations, the lamp transformer derives its input directly
from a line voltage-regulating transformer, selected for its ability to main-
tain a constant output voltage level regardless of fluctuations in the input
line voltage within the control range of 105 to 130 VAC.
In some applications where we have an abundance of energy due to
low sample absorption, the focusing lens is removed to avoid excess
energy reaching the detector. However, other systems have high energy
2–2
Teledyne Analytical Instruments
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Circuit Descriptions