Reference Manual
Chapter
3
Ruler E
Configuring the Ruler
Cycle Time and Exposure Time
The cycle time – that is the time between two profiles – and the exposure time – the time
during which the sensor is measuring the light from the object – can be set separately
when configuring the Ruler.
However, the exposure time cannot be longer than the cycle time. Therefore, if the expo-
sure time is set to be longer than the cycle time, the cycle time will be used as the actual
exposure time.
If the exposure time instead is set to be shorter than the cycle time, the Ruler will reset the
sensor at the beginning of each cycle and then read the exposure after the specified time.
The Ruler uses a
rolling shutter
– that is, it reads out the exposure on the sensor one row
at a time, and at the same time resets that sensor row. Thus, reading the entire sensor
image takes a certain amount of time.
When the exposure time is equal to the cycle time, the Ruler only needs to go over the
sensor once every cycle. Therefore the shortest possible cycle time would be the same as
the time it takes to read the sensor.
But when the exposure time is shorter than the cycle time, the Ruler needs to go over the
sensor twice – once for resetting the sensor and once for reading the exposure. Resetting
the sensor takes just as long time as it takes to read the exposure, which means that the
shortest possible cycle time would in this case be two times the read-out time.
When triggering profiles with pulse triggering, the exposure time should be set to be
shorter than the cycle time, otherwise the sensor will be exposed during the entire cycle.
This time may vary since it is depending on the pulse trigger signal, leading to varying
exposure times.
Figure 3.3 - Exposure time when set to longer and shorter than the cycle time.
Read-out
Cycle time
Used exposure
time
Read-out
Cycle time
Reset
Exposure time
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