23
PerkinElmer
Optoelectronics
7 Target Speed Determination
7.1 Target Speed and Exposure Relationships
The following definitions apply:
Image Resolution
The number of pixels in the camera sensor array.
Spatial Resolution
The sensor array pixel dimensions mapped onto the
web dimension X. (See Table 3.)
Feature Resolution
The smallest feature to be imaged by the camera.
The target speed derives from the chosen feature size D and is limited by the
minimum Line Period values defined in Tables 1 and 2. The chosen feature size
must equal at least 2 times the effective Y spatial resolution to satisfy the Nyquist
criterion such that at least 2 effective contiguous y samples are provided for
unambiguous detection of the feature of size D.
The effective y resolution is defined by the static spatial resolution plus an
effective y dimension elongation that is determined by the target velocity and
time of exposure. The choice of D must satisfy the following:
pixels
of
X
D
y
eff
#
2
>
=
Once D has been chosen then the target velocity is determined by:
Period
Line
Min
y
V
eff
web
.
=
The following is a derivation of the relationships that define the effective Y
spatial resolution
eff
y
in terms of target velocity
web
V
and exposure time
exp
t
.
The static spatial resolution is:
pixels
of
X
y
x
static
static
#
=
=
The effective spatial resolution
eff
y
due to target velocity
web
V
along the y axis is
given by:
exp
exp
*
#
*
t
V
pixels
of
X
t
V
y
y
web
web
static
eff
+
=
+
=
from which the exposure
exp
t
may be calculated given a target velocity
web
V
as
follows:
web
eff
V
pixels
of
X
pixels
of
y
t
*
#
*#
exp
−
=
Summary of Contents for RETICON LD3500 Series
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