Chemical Engineering April 2012 - 54

Feature Report
Engineering Practice
New Measurement
Practices for
Cold Climates
New approaches improve reliability
and reduce costs in environments with
extremely cold temperatures
Mark Menezes
Emerson
I
nstrumentation best practices that
are taught in colleges and published
in standards are intended
to be broadly applicable, guiding
users in every industry and geography.
However, for outdoor applications in
cold climates, where the temperature
can fall below -40°C, the optimum installation
may be very different from
those recommended via best practices,
to ensure reasonable performance, reliability
and lifecycle cost.
New best practices for making measurements
in cold climates have been
identified using advanced transmitter
diagnostics, digital protocols and
asset-management software. Together,
these new technologies give users and
equipment suppliers unprecedented
insight into device performance and
failure modes in real applications.
As this article demonstrates, many
of the traditional practices for managing
instrumentation are not ideal for
cold climates. For instance, traditionally,
transmitters used in cold climates
have been:
* Installed in heated enclosures. As an
alternative, operators should heat
the sensing lines only. This reduces
cost and improves reliability
* Mounted below the pipe for steamflow
applications, with a heated wet
leg (discussed below). As an alternative,
operators should install the
FIGURES 1A and
1B. Using a device
dashboard and timestamped
diagnostic
log, complex, diagnostic
information
about this pressure
transmitter is presented
in an easy-tounderstand
format,
for easy troubleshooting.
All events and
failures are logged in
non-volatile memory,
with date-and-time
stamp, for easy
post-mortem failure
analysis
transmitter above the pipe and the
configuration should have no wet
leg. This reduces cost and improves
reliability
* Connected to the process via heated
capillaries in level applications.
Instead, operators should use electronic
remote sensors. This reduces
costs, improves performance, reduces
spares and simplifies installation
and maintenance
Diagnostics, digital protocols
Several tools have emerged during
the past decade [1] to identify and justify
improved measurement practices.
These include advanced device diagnostics
and the proliferation of digital
protocols, such as HART, Foundation
Fieldbus or Profibus fieldbus or the
newer WirelessHART or ISA 100.11a.
54 CHEMICAL ENGINEERING WWW.CHE.COM APRIL 2012
These advances can help users to detect,
predict and even automatically
correct for problems in the device sensor
and electronics, the power supply
and wiring, the environment, the process
connections and in the process
itself.
Not surprisingly, since a key stressor
in a cold climate is low temperature,
diagnostics that measure and
trend process and device temperature
were useful in identifying the new
practices described below. For example,
in a pressure transmitter, the sensor
temperature measurement is used
internally by the smart transmitter
microprocessor to automatically compensate
for expansion and contraction
of the oil and mechanical components,
which improves the accuracy of the
pressure measurement.
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Chemical Engineering April 2012

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