Teledyne 5000B - Near Infrared Photometer - Manual (Page 95)

Part II: Maintenance/Analysis Unit Maintenance 5
Part II: 5-5 Teledyne Analytical Instruments
The procedure is purely mechanical and consists of adjusting the amount of
light passing through either the measuring or reference filter, never both. Screens
(wire mesh) of varying density are used for this operation and are part of the small
took kit accompanying the instrument.
1. Observe the oscilloscope and judge if optical balancing is
needed. When the difference is less than 1 volt, balancing is not required. The
tallest of the two peaks should be adjusted to 8 or 9 volts with the gain control
R2 on the detector PC board. When this cannot be done because both peaks are
too short or too long, search for screens mounted in the light path, usually located
in a holder on the light pipe which interconnects the detector and sample module,
and remove or add screens, as necessary.
2. When balancing is needed, identify the peaks as outlined under
Section
3. For example, if the reference peak is the shorter one, stop the
filter wheel with your hand and see if screens are located behind the reference
filter. The reference filter is identified by the letter “R” engraved on the filter
wheel.
4. If screens are found, remove them after taking the filter wheel off
the shaft with the special Allen wrench supplied in the tool kit.
5. After removal of the screens and remounting the filter, mount the
filter wheel back on the shaft. Position it correctly on the shaft by lining up the
two paint marks on shaft and wheel.
6. Turn on the instrument and observe the balance on the oscillo-
scope.
a. If the reference peak is now too tall, remove the filter wheel and
add a screen of lesser density behind the reference filter. Repeat this procedure
until the peaks are within 1 volt of each other.
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.