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CIP System Instrumentation and Controls 127
water and the overall design of the vessel can interfere with proper performance of
these devices.
Supply Pressure Monitoring and Control
Unlike their level sensing counterparts, the use of modern sanitary diaphragm
type pressure transmitters to measure CIP supply pressure will work very well as
the effects due to temperature variation are almost negligible. Also the role of the
pressure transmitter is much less critical in nature and is generally used as more of a
monitoring device than regulating device in CIP applications.
Many applications interlock the chemical feed sequences and the heating
controls so that these systems cannot be operated if aminimum supply pressure is
not maintained. This is implemented as asafety measure toprevent steam and
chemicals to be applied to the system when the supply pump is not discharging
water or CIP solution. This interlock function could also be readily applied utilizing
a minimum flow setpoint instead and is frequently the means utilized in
pharmaceutical applications.
Return Flow Check
For years the food and dairy industry has incorporated instrumentation in the CIP
return line to check and verify that the first pre-rinse ofthe CIP program has
successfully returned back to the CIP unit. Failure of the return flow check would
result in an aborted CIP program along with an appropriate alarm message to the
operator.This functionality was primarily provided to ensurethat all manual swing
connections on the CIP supply side and CIP return side were configured properly.
Even with the advent of fully automated hard piped mixproof valve systems, it is
still considered good practice to include this functionality in all applications,
including pharmaceutical.
The Conductivity Sensing Element
The instrument of choice for many years has been an inexpensive sanitary stainless
steel probe mounted in an insulating material and clamped in place within a
shallow tee fitting. The probe is, in turn, wired to arelay designed to trigger based
upon the difference in conductivity between air and water. These conductivity
probes were originally designed to be used for discrete liquid level controls, but
have also served reliably in this application many times over.One must be careful to
specify an appropriate relay with aconductivity range which will work with the
water to be used in the application, however. Water such as water-for-injection will
require avery sensitive relay that can detect very low conductivity levels.
Recently, some pharmaceutical users have rejected the use of these devices as
the manufacturers of them have been slow to provide proper material certifications
and/or performance specifications for their products. Hopefully, this situation will
improve over time such that product acceptance will not be aproblem.
The “Tuning Fork”
Amore recent alternative to the conductivity-based device is another instrument
that was designed originally with level sensing in mind. The “tuning fork” level
switch utilizes apair of paddles that vibrate at aknown resonant frequency. When
the forks are immersed in aliquid, the frequency changes and the associated
electronics detect the change. These tuning fork devices have also been used