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Chapter
Real-Time Control Issues
Background
Real-time control is an important issue in
most IR machine vision systems used for
automated temperature monitoring and
inspection. Having said that, it should be
noted that real time tends to be a relative
term, the measure of which varies with
the application and user requirements. In
some applications, users would consider
a response time of 100 milliseconds to
meet their denition of real-time. On
the other hand, many electronic events
are extremely fast or short-lived, and a
one-microsecond response might be
needed. As mentioned in earlier chapters,
process temperatures tend to change
relatively slowly, so an IR machine vision
system that can update images and
temperatures every 10-100ms, or even
less frequently, may be adequate.
Hardware and Software Platform
Considerations
In most cases, a PC with a Microsoft
Windows operating system (OS) isn’t
well suited for controlling fast, real-time
applications. Windows is referred to as a
non-deterministic OS because it typically
cannot provide predictable response
times in critical measurement and control
situations. Therefore, the solution is to
link the PC to a system that can operate
autonomously and provide rapid,
predictable responses to external stimuli.
Deterministic applications (those
intended to be event driven) are
controlled better with systems based
on an embedded microprocessor and/
or digital signal processor (DSP) that
has a dierent type of OS – or perhaps
a special version of Windows other than
the ones typically found on a home or
Figure 1. PLCs are a good choice for creating deterministic (event-driven) systems, supported by a
PC that is used for data trending.
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