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5.2
Full Scale Adjustment
The Sensor Head has been set at the factory and should not have to be re-
adjusted under normal circumstances. Should it be necessary to re-set the
spacing of the sensor head, the following procedure should be followed:
1. Mount the STM-1 or STM-2 System Test Module in the Faraday Cage.
2. Select the MAN mode and adjust the charging voltage to +5.0 kV.
3. Adjust the SAMPLE CHARGE meter (SCm) for zero using the ZERO adjust
knob.
4. If using the STM-1 place the system in CHARGE then set the FULL SCALE
ADJUST control to the STM-1 position. If using the STM-2 set the FULL
SCALE ADJUST control to the NORM position. The SCm should read
+5.0kV. If not, adjust the control slightly to obtain +5kV. If not, loosen the
Sensor Head retaining clamp screw and move the sensor forward to increase
the SCm reading and conversely, rearward to decrease the SCm reading.
Make certain the sensing part in the Sensor Head is always in the 12 o'clock
position and appears centered in the viewing hole in the Faraday Cage.
Retighten the retaining clamp screw.
When testing static dissipative or conductive composite or laminated films
use a known good sample to adjust the full scale using the adjust control if
the STM-1 was used for the initial system check. If the STM-2 was used, this
step is not necessary.
The full scale setting is critical for these types of material. If the charge
is conducted onto the material the SCm will read the fully applied 5kV. If the
charge was induced onto the material, the SCm will indicate an accepted
voltage level that is several hundred volts less, depending on the thickness of
the material. When the decay time is measured, the SCm will drop very
quickly due the collapse of the electrostatic field on the electrodes and the
buried conductive layer leaving a small residual charge that remains on the
non-conductive or dissipative outer layer. If this remaining charge is greater
than the cut off level the clock will run on. However, if it is less than the cut
off level the clock will indicate a very fast decay time (<0.01sec) If the outer
layer is dissipative, the SCm will drop rapidly then bleed off the remaining
charge and the clock will indicate a measurable decay time.
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