Reference Manual Chapter 5
Ranger E/D
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Configuring Ranger E and D
5.6 Setting Exposure Time
Once the height of the ROI is set, there are two other settings that affect the profile rate of
the Ranger:
Cycle time The time between two scans when measuring in free-running mode.
Exposure time The time during which the sensor rows in the ROI is exposed.
For natural reasons, the exposure time cannot be longer than the cycle time. If the expo-
sure time should be set longer than the cycle time, the Ranger will expose the sensor rows
during the entire cycle.
If the exposure time is instead set to be shorter than the cycle time, the sensor rows are
reset at the beginning of the cycle. The exposure is then read from the sensor after the
specified exposure time.
If the Ranger is measuring in free-running mode, measuring without the explicit reset will
work well since the cycle time (and thus the exposure time) is constant. However, if the
Ranger is measuring in pulse-triggered mode, the cycle time may vary since it now de-
pends on the pulse triggering signal. Varying cycle times will in this case result in meas-
urements made with different exposure times. To guarantee a constant exposure time, the
exposure time should be set to be shorter than the cycle time, thereby enabling the explicit
reset of the sensor rows. However, resetting the sensor takes a certain time.
Measuring with a certain exposure time and resetting the sensor rows will therefore
require a longer cycle time than measuring with the same exposure time but without the
reset.
The time it takes to reset the sensor rows within a ROI is equal to the shortest possible
exposure time for the ROI. Both the reset time and the shortest possible exposure time
depend on the height of the ROI.
Thus, when using the shortest possible exposure time, the shortest possible cycle time
(and thereby the highest possible profile rate) is:
The exposure time, when measuring without reset
Approximately two times the exposure time, when using the explicit reset
Figure 5.7 – Exposure times and cycle times in different combinations of reset and trig
modes (continued on the next page).
Free
running with no explicit reset
Pulse triggering with no explicit reset
Cycle Cycle Cycle
Cycle Cycle
Exposure time
Cycle
Exposure time Exposure time
Tri
Tri
Tri
Cycle time
Min. cycle time
Time
Time
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