IMPORTANCE OF CALIBRATION AND TRACEABILITY
10.0. IMPORTANT OF CALIBRATION
What is calibration?
Calibration is a
comparison between a known measurement (the standard) and the measurement using
your instrument. Typically, the accuracy of the standard should be ten times
the accuracy of the measuring device being tested. However, an accuracy ratio
of 3:1 is acceptable by most standards organizations. Sure Controls provides preventative
field service to help you ensure your instruments and controls
are accurately calibrated.
Calibration of your
measuring instruments has two objectives: it checks the accuracy of the
instrument and it determines the traceability of the measurement. In practice,
calibration also includes repair of the device if it is out of calibration. A
report is provided by the calibration expert, which shows the error in
measurements with the measuring device before and after the calibration.
To explain how
calibration is performed we can use an external micrometer as an example. Here,
accuracy of the scale is the main parameter for calibration. In addition, these
instruments are also calibrated for zero error in the fully closed position and
flatness and parallelism of the measuring surfaces. For the calibration of the
scale, a calibrated slip gauge is used. A calibrated optical flat is used to
check the flatness and parallelism.
Why calibration is important?
accuracy of all measuring devices degrades over time. This is typically caused
by normal wear and tear. However, changes in accuracy can also be caused by
electric or mechanical shock or a hazardous manufacturing environment (e.x.,
oils, metal chips etc.). Depending on the type of instrument and the
environment in which it is being used, it may degrade very quickly or over a
long period of time. The bottom line is that calibration improves the accuracy
of the measuring device. Accurate measuring devices improve product quality.
measurement instrumentation is something that should never go overlooked. To
calibrate instrumentation means to determine, check, or rectify the graduation
of any instrument giving quantitative measurement. Calibrating a device ensures
that the instrument will properly measure within the desired range for your
application. This is important because a properly calibrated measurement device
will help the user to maintain his or her system. A device can be
calibrated either at the factory where the device was manufactured or
within the field. Calibration certificates may be obtained once a
device has been calibrated.
a device is calibrated at the factory, the device is factory calibrated.
When a device is factory calibrated, the manufacturer will ensure the device is
properly reading within its designed range and meets specifications. This is
best for when a user is intending to quickly put a device to work once
it has been received. This type of service may add a nominal fee and
increase the time it will take for the product to be shipped; but, it will
also allow the user to quickly put the device to work, offsetting both the cost
and time of factory calibration.
a device is calibrated on sight at the location where it will be used, the device
is field calibrated. This is ideal if the device will be
communicating with multiple devices in an integrated system. By field
calibrating the device, the user will be able to set the parameters
required for the device to work properly within the system. Field
calibration is common for devices that may not be removable once installed.
Typically, manufacturers will provide guidance has to how to properly calibrate
a device in the field, within the product’s specifications and without
damaging the device or voiding warranty.
require a device to have a calibration certificate. A common certification for
measurement devices is a NIST/NABL calibration certificate. NIST stands for
the National Institute of Standards and Technology
/ NABL stands for National Accreditation Board for Testing and Calibration
Laboratories and they strive to enhance productivity, facilitate trade,
and improve quality of life. For NIST/NABL calibrations, the institute will
supply standard reference material (SRM) for devices to be calibrated against.
A certificate of analysis and material safety data sheet are provided with
every SRM sent out. The certification means that the device was tested against
the SRM and met required specifications by the NIST/NABL. NIST/NABL calibration
certificates do come with expiration dates, so this means that for the device
to keep its certification, it will have to be retested against a NIST/NABL standard
reference material (SRM). When a device receives a Traceable NIST/NABL
Certificate that means the device was tested against another device with a
paper trail leading back to a NIST/NABL standard reference material (SRM). A
NIST/NABL Calibration Certificate proves that a product has been tested to
ensure accuracy, and helps ensure a precision device is able to achieve the
highest possible levels of measurement quality and productivity. This is often
required in validated or regulated applications, such as pharmaceutical or food
instrumentation sometimes offer factory and certificates of calibration. They
are able to provide this service for new purchases as well as existing products
that may require recalibration from time to time. Manufacturers often
keep copies of the calibration, creating a documentation back-up for the
instrument. By letting the manufacturer provide calibration services, you
can take advantage of their instrumentation expertise, to ensure the
calibration has been done correctly, save time calibrating, and maintain
back-up documents for calibration.
When should you calibrate your measuring device?
A measuring device
should be calibrated:
to the recommendation of the manufacturer.
any mechanical or electrical shock.
(annually, quarterly, monthly, weekly, daily, hourly)
The hidden costs and risks associated with un-calibrated measuring device could be much higher than the cost of calibration. Therefore, it is recommended that the measuring instruments are calibrated regularly by a reputable company to ensure that errors associated with the measurements are in the acceptable range.