25
Combining Machine Vision and
Temperature Measurement
Combining Machine
Vision and Temperature
Measurement
Background
Traditionally, visible light cameras have
been a mainstay in machine vision
systems used for automated inspection
and process control. Many of these
systems also require temperature
measurements to assure product quality.
In numerous cases, an IR camera can
supply both an image of the product
and critical temperature data. If the
application will not benet from
thermographic images and non-contact
temperature measurements, then a
visible light camera is certainly less
expensive. If the opposite is true, then an
IR camera should be considered by the
system designer.
As the sophistication of IR cameras
continues to increase, along with
associated hardware and software, their
use in automated systems is growing
rapidly. Because of their combined
imaging and temperature measurement
capabilities, they can be very cost
eective. The main impediment to their
wider usage is system designers’ lack
of familiarity with IR camera features
and the related standards, systems, and
software that support them. This chapter
supplies a good deal of that information.
Machine Vision Applications
As in the case of visible light cameras,
thermographic cameras and their
associated software can recognize the
size, shape, and relative location of
target objects (i.e., they can do pattern
matching). Moreover, the electronics
in newer IR cameras provide fast signal
processing that allows high video frames
rates (60Hz or higher) to capture relatively
fast-moving parts on a production line.
Their A/D converters combine short
integration times with 14- to 16-bit
resolution, which is critical for properly
characterizing moving targets or targets
whose temperatures change rapidly.
Figure 1. Results of automated inspection of ICs
on a circuit board
One example of the latter is automated
inspection of operating ICs on a circuit
board (Figure 1). In some cases, this
involves overload testing in which an
IC is subjected to a current pulse so its
heat loading can be characterized. In one
such case the IC is forward and reverse
biased with current levels outside of
design limits using a pulse that lasts
800ms. The IR camera captures images
during and after the current pulse to
characterize temperature rise and fall.
With a 60Hz frame rate, a new frame can
be captured about every 17ms. In such a
system nearly 50 frames can be captured
during the 800ms pulse, and many more
Chapter 4
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