3
How the T-212 Target Measures Angle
Figure 4 shows how the T-212 Target measures angle. It uses a lens that has a 1-inch focal length, which
means any deviations detected by the PSD sensor are expressed in inches/inch (mm/25.4 mm). To
understand this better, imagine that there is another PSD sensor 1 inch behind the where the T-212’s PSD
is actually located. So any angular changes in the target will produce different readings for the PSD in
the actual location versus the reading in the “virtual” location.
For example, if the readout shows a vertical reading of .001 in. in angular mode, this indicates the laser
beam is located on the virtual PSD a .001in. higher than its location on the actual PSD.
Another way to think about is it’s a lot like using a dial indicator to take a measurement for center in one
location along on a bar (or bore) and moving along the bar (or down the bore) and taking a second
measurement. When the second measurement is subtracted from the first, the results shows the pitch and
yaw of the axis of the bar (or bore) relative to the mechanical axis used to support the indicator.
Figure 4 –
Measuring Angle with the T-212 Target
With the T-212, this “subtraction” is accomplished automatically using an optical lens, so the user can
view the angular pitch and yaw of the axis of the target relative to the axis of the laser beam on the
readout without performing any calculations. The axis of the laser beam represents where the target
ought
to be, the axis of the target represents where is actually
is
, and the difference between the two displays on
the readout.
How the T-212 Target Measures Center
With the lens module removed, the target operates in Centering Mode. After the lens module is removed,
insert the light shield in its place. There is no particular orientation for the light shield.
In Centering Mode, the target is sensitive to vertical and horizontal displacement. The target is sensing at
the plane of the cell and the readout displays the position of the target relative to the laser beam if the
target is high or low and left or right relative to the laser beam).
Figure 5 –
T-212 with Light Shield in Center Mode
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