Teledyne 6600 - Manual (Page 68)

1-4 Part II
1 Operational Theory Model 6600
Teledyne Analytical Instruments
To obtain analyzer options that are linearly related to the concentration
of the component of interest, the output of the I to E converting amplifier is fed
to the input of a logarithmic amplifier, which produces a signal that represents
the logarithm of the output signal of the second amplifier. The output of the
logarithmic amplifier is fed to the input of an inverting amplifier, which acts like
a buffer between log amplifier and switch and inverts the input signal for further
processing.
The output of the inverting amplifier is fed to a magnetically activated
SPDT reed switch, synchronized in such a way that all measuring pulses are
collected on one switch contact and all reference pulses on the other.
The pulses pass through diodes that isolate the integrating networks
from each other. The integrators convert the reference and measuring pulse
energy to a DC level representing them. These reference and measuring DC
levels are applied to the subtracting amplifier in the Control Unit. The output
of the subtractor is a DC voltage linearly related to the concentration of the
component of interest.
From the subtractor, the signal progresses to the analog to digital
converter on the motherboard of the Control Unit.
The microcontroller reads the A to D converter and displays the result
on the front panel.
The procedure to set up the optical bench, the signal processing front-
end amplifiers, the standardization of outputs, and alarm systems are described
in separate sections of the manual.
1.4 Automatic Zero System
To compensate for zero drift, which may occur during sampling, the
analyzer zero reading is updated by the Auto-Cal function of the controller. An
electronics timing circuit provides a timing cycle that is user programmable.
The Auto-Zero system is turned off (see chapter 3 section 5). You have
the option of setting the analyzer for one six minute zero cycle during hourly
intervals of time from one to 23 hours, and daily from one to 30 days.
The Auto Zero system compares the present zero reading of the zero
fluid with the zero reading of the zero fluid as it was in the last zero calibration.
When there is a difference, the electronic zero circuit sets the zero reading to