Efficient Plant March 2018 - 36

instrumentation

Field or Workshop
Calibration?

How and where to perform process-instrument calibration depends on various factors.

IS IT BETTER to calibrate process instruments in the field or in a workshop, i.e, on
a bench? That's a question frequently posed to experts with Beamex, Marietta, GA (beamex.com). According to a blog post by Heikki Laurila, the correct answer depends on
various factors. He offered the following arguments for these different types of calibration approaches.
- Jane Alexander, Managing Editor

Heikki Laurila is a frequent blogger for Beamex Oy Ab (Pietarsaari, Finland).
Read more of his posts at blog.beamex.com.

36

| EFFICIENTPLANTMAG.COM

+

FIELD CALIBRATION

+

WORKSHOP CALIBRATION

The field approach (the most common method)
ensures that instruments are calibrated under
actual operating conditions. It also can be more
effective than workshop calibration, assuming that the
field instruments have been designed and installed
for easy access.
If you want to calibrate a complete measurement loop
in one go, from the measurement point in the field to
the control room display, you'll need to go out in the
field to start from the process sensor/transmitter. If
the total loop has too big of an error, then the individual parts of the loop need to be calibrated separately.
If you don't want to remove-or can't remove-an
instrument from its installed location, field calibration
is, essentially, your only option.

Sometimes, actual field conditions can be very challenging/harsh. In those cases, workshop calibration
is more appropriate. Plus, in a dedicated workshop,
all required equipment is typically at hand and ready
for use. While usually less efficient, in the long run,
workshop calibration can be more ergonomically
friendly, not to mention more convenient, than field
calibration.
If you calibrate instruments during the commissioning phase, i.e., before they are installed in the field,
it's more convenient to do so in a dedicated calibration workshop.
If your requirement is "best possible uncertainty,"
it's often easier to get better total uncertainty in a
workshop than out in the field. This is achieved
using dedicated stationary, high-accuracy calibration
equipment and controlled environmental conditions
and processes.
If you use rotating spares, or want to calibrate loose
spare devices before installing them in the field, doing so in a workshop is the most practical approach
and can offer the same efficiency gains. EP

MARCH 2018

http://www.beamex.com http://blog.beamex.com http://www.EFFICIENTPLANTMAG.COM

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