Teledyne 6020 - Photometric analyzer - Manual (Page 84)

3 Maintenance Model 6020
3-6 Part II Teledyne Analytical Instruments
b. If the measuring peak is equal to or within 1 volt of thereference peak,
the system is optically balanced and ready for calibration.
c. If the peak is still too short, repeat the procedure, but thistime put a
screen behind the measuring filter to shorten its peak.
7. After the peaks are balanced, adjust the gain control until the tallest
of the two peaks is 8 to 9 volts. The peaks should still be within1 volt of each
other.
8. It is always good practice to operate the analyzer with as low a gain
as possible. Therefore, with the gain control just barely off its stop, once again
remove or add screens in the light path to obtain as high a voltage as possible
without exceeding 9 volts for the highest peak. Read-just gain for 8 to 9 volts.
This concludes the balancing procedure and the instrument is ready for
calibration.
3.5.6 Setup of the Logarithmic Amplifier
The amplifier is inverting and continuously taking the logarithm of the
output signal of the second amplifier. You can observe the output by connecting
the scope probe to TP4.
The correct wave shape has a rounded negative going pulse that is the
signal and a flat-topped positive pulse that depicts saturation of the log amplifier.
You should not permit distortions or oscillations in the rounded peaks.
When the positive going pulse is not flat or is distorted, adjust trimpot R3
only enough to obtain a flat positive pulse. If you over adjust, you may lose part
of the second decade of absorption and affect the accuracy of analysis for high
concentrations of the component of interest where the measuring pulse can
become very short. The log amplifier saturates because the amplifier is
incapable of taking the logarithm of the slightly negative baseline.
3.5.7 Inverting Amplifier
The amplifier is inverting and has a gain of 1. It inverts the output signal
of the logarithmic amplifier and acts as a buffer between the logarithmic
amplifier and the reed switch and integrators. To observe the output of the
inverter, connect the scope probe to TP5. The wave must be a duplicateof that
observed on TP4, except that it is inverted.