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7 CIP System Instrumentation and Controls
INTRODUCTION
Barry J. Andersen
Seiberling Associates, Inc., Beloit, Wisconsin, U.S.A.
Successful clean-in-place (CIP) operations require acontrolled combination of time,
temperature, chemical concentration, and mechanical action to provide satisfactory
performance on a repeatable basis. This chapter discusses and reviews the
instrumentation and control concepts required to ensurethat above criteria aremet.
This chapter will consider the following items:
& Common instrumentation utilized to control the CIP process and verify
system performance
& Review performance requirements as they relate to the selection of programmable
logic controller (PLC) systems and distributed control systems (DCSs)
& Software development concepts as they relate to CIP
& CIP System Quality Control Tools
ABASIC CIP UNIT MODEL
A basic recirculating CIP unit model is shown in Figure 1. The minimum
instrumentation and control elements required to control time, temperature,
concentration, and mechanical action are highlighted in this diagram. The intent
of this model is not to illustrate the actual mechanical details of aCIP system (as in
Chapter 6) but to identify the most basic instrumentation and control needs for
any application.
A brief discussion of the various components utilized to achieve this
control follows.
Time Control
In the very early days of CIP, the control systems used for these applications
generally consisted of relays, cam timers, and stepping switches. The cam timer
served as areliable and accurate means of controlling the lengths of various steps of
the CIP program, including the duration of the chemical wash steps. Today’s PLC
systems and DCSs provide the required timing functions in software that replaces
all of the old hardwired devices. Time control today is merely a function of
adjustable variables within the operating programs for the system. Although it is
easy to take time control for granted with today’s modern control systems, there are
many important decisions to be made during development of the CIP programs
that have adirect impact on how well the system performs for all of the required
circuits. The programmer must take into consideration the circuit-specific timed
functions, which require flexibility (and are generally recipe driven), versus
equipment-parameter timing functions that are non–circuit specific. Errors are
often made in the development of these programs that cause flexibility limitations
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