Instruction manual

21 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 Figure 5 on page 9)
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 Table 1 on page 8. 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 + an effective
y dimension elongation that is determined by the target velocity and time of
exposure. The choice of D must satisfy the following:
pixelsof
XD
y
eff
#2
>=
Once D has been chosen then the target velocity is determined by:
PeriodLineMin
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:
pixelsof
X
yx
staticstatic
#
==
The effective spatial resolution
eff
y due to target velocity
web
V along the y axis is
given by:
expexp
*
#
* tV
pixelsof
X
tVyy
webwebstaticeff
+=+=
from which the exposure
exp
t may be calculated given a target velocity
web
V as
follows:
web
eff
Vpixelsof
Xpixelsofy
t
*#
*#
exp
-
=