Chemical Engineering June 2019 - 42

Feature Report
Professional Calibration
Supports Operational Excellence
Apart from ensuring the conformity of the process and the quality of the product, professional
calibration, first and foremost, improves the quality of the process
Dimitri Vaissiere
and Pia Höfflin
Endress+Hauser
IN BRIEF
WHY CALIBRATE
A SOUND APPROACH TO
CALIBRATION
CALIBRATION INTERVALS
INTERVAL OPTIMIZATION
DEVIATION
MANAGEMENT
PERFORMING
CALIBRATIONS
BENEFITS OF
ACCREDITATION
TIME-SAVING METHODS
TOWARD INTEGRATED
INTELLIGENCE
PUTTING IT ALL
TOGETHER
A
(CPI),
during
t many plants
in the chemical
process
instrumentation
usually
maintenance
industries
measurement
is
calibrated
scheduled
downtimes.
This basically
means that metrological
requirements
are
regarded as secondary
to operational
needs. The objective
seems to be to produce
a complete set
×
×
=
Availability
Performance
Quality
OEE
Endress+Hauser
Theoretical production time
Planned production time
Gross operating time
Net operating time
Valuable
operating time
Quality
losses
Speed
losses
Unplanned
downtime losses
Planned
downtime
FIGURE 1. Availability, performance and quality are the three quantifiable components of the
overall equipment effectiveness (OEE)
of calibration certificates to pass the next
audit again. Although this approach seems
to be practical, in fact, it misses the point:
professional calibration management is
aimed at safe and efficient production processes
and optimal product quality.
Why calibrate?
Calibration should not be considered primarily
as a means to obtain a certificate for
regulatory reasons. Calibration is much more
than just a question of compliance. Rather,
it affects the overall equipment effectiveness
(OEE), and lacking or inadequate calibration
might result in increased expenditures.
Availability, performance and quality are
the quantifiable components of OEE (Figure
1). All of these three can be affected by incorrect
measurements. Availability may be
impacted where failing devices might result
in shutdowns. Performance suffers when
drifting measurements call for corrective actions
time after time. In addition, incorrect
measurements may be responsible for waste
in raw materials or production loss.
Of course, process instrumentation does
42
not come for free. There are the inevitable
direct costs of maintenance and calibration,
for example (Figure 2). But on the other
hand, apart from the above-mentioned issues
arising from poor measurements,
working with inaccurate readings can cause
unnecessarily high consumption of energy
and raw materials.
To avoid the numerous details of common
textbook knowledge we would like to simply
summarize the purpose of calibration as
follows, just to provide an operational definition:
those who calibrate a measurement
instrument are determining whether and to
what extend the measured value deviate
from the reference value given by a measurement
standard. If the deviation exceeds
the tolerance - generally called maximum
permissible error (MPE) - the instrument
likely needs to be adjusted, repaired or replaced.
This applies to all types of measuring
devices, whether they measure physical
quantities, such as flow, pressure and temperature,
or chemical parameters, such as
pH, conductivity, dissolved oxygen and so
on. The calibration method for both of these
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Chemical Engineering June 2019

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