PASCO AP-8215A Gravitational Torsion Balance - Manual (Page 18)

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G r a v i t a t i o n a l T o r s i o n B a l a n c e M a i n t e n a n c e
14
Maintenance
Replacing the Torsion Ribbon Assembly
If the torsion ribbon breaks, replace it as follows:
1. Remove the plates, and raise the locking mechanism using
the locking screws until the pendulum arms are securely
anchored (Figure 21a).
2. Grasp the pendulum bob near the bottom ribbon tab to sta-
bilize it.
3. Loosen the Phillips screw on the bottom tab of the torsion
ribbon assembly (Figure 21a), and remove the bottom half
of the broken ribbon assembly.
4. Loosen the Phillips screw at the top of the balance assem-
bly (Figure 21b).
5. Grasp the torsion ribbon head and remove the top portion
of the broken torsion ribbon assembly.
6. Attach the top tab of the new torsion ribbon to the torsion
ribbon head using the Phillips screw, being sure the cop-
per disc on the tab is in contact with the torsion ribbon
head (Figure 22). Align the tab with the face of the torsion
ribbon head.
7. Thread the ribbon through the shaft.
8. Using the zero adjust knob, align the bottom tab with the
face of the pendulum bob.
9. Tighten the Phillips screw on the top of the balance to secure the torsion ribbon head.
10. Attach the bottom tab of the ribbon to the pendulum bob using the Phillips screw.
11. Replace the back plate.
12. Level and align the pendulum according to the instructions in the Equipment Setup section of this manual.
Broken
torsion
ribbon 1 . Turn locking screws until the
locking mechanism anchors the
pendulum arms.
Locking
mechanism
3 . Loosen the
Phillips screw.
4. Loosen the
Phillips screw.
5. Grasp the torsion ribbon head
and remove the top portion of the
broken ribbon assembly.
b
Figure 21: Securing the pendulum bob
before removing a broken torsion ribbon,
and loosening the torison ribbon head.
Zero adjust
knob
Torsion
ribbon
The copper
disk must
contact the
torsion ribbon
head.
Ribbon tab
Torsion ribbon
head
Attach the tab
with the Phillips
screw.
Figure 22: Attaching the top tab of the torsion ribbon
assembly to the torsion ribbon head.
Note: Be sure the ribbon is not twisted.
2 . Grasp the pendulum
bob here to stabilize it.
a