Page 25 - EngineerIT September 2022

MEASUREMENT AND INSTRUMENTATION

Most of the early measurement units were based on
quantity, volume, mass, distance, angles and time, but as the
human race evolved and technology became more advanced,
there was the need for additional measurements such as
electrical, frequency, temperature, pressure, etc…
Over time, as trade between different nations and regions
increased, a standard comparable reference system was needed
in order to measure. In 1585, the stirring started with Simon
Stevin when he proposed a decimal system that eventually,
after many different iterations, lead to our modern metric
standardised system.
The SI system is continually developing to keep track with
ever-evolving technologies.

Calibration and intermediate checks/verifications
What’s the difference – what’s the RISK if any?

The first two very important definitions from the international
vocabulary of metrology that will be used in this article are:
• Calibration 5.18 [VIM3: 2.39; VIM2: 6.11; VIM1: 6.13]
- Operation performed on a measuring instrument or a
measuring system that, under specified conditions:
1. establishes a relation between the values,
with measurement uncertainties provided by
measurement standards and corresponding
To Measure is to know indications with associated measurement
To calibrate is to be Accurate uncertainties and
To Verify is to be assured of Accuracy 2. uses this information to establish a relation for
obtaining a measurement result from an indication.
• Verification 5.25 [VIM3: 2.44] - Provision of objective
The calibration story of value continued evidence that a given item fulfils specified requirements.
Today we live in a world where quality systems have been
adopted and implemented to improve the overall quality and When we only comply with our quality system requirement
efficiency of the output of industry. of an annual calibration, we may inherently and unknowingly
And with these quality systems came requirements of introduce a risk. When only performing calibration and
calibration. adjustment on an annual cycle, an instrument comes back
A question to ask - do these calibration requirements add showing that it was out of specification. Can we trust the
value – the answer is a definite YES!!! measurements we have made with that instrument since the
But……. last time it was “calibrated”?
What do quality systems say about calibration intervals and
validity? Once a year? Twice a year? Once every two years?

The short answer is they do not specify this based on time but
rather on the risk to quality coupled to use, criticality and initial
validity. This is because instrumentation and measurement tools
change with exposure to:
• The passage of time
• Temperature and variation in temperature
• Humidity and variation in humidity
• Changing environmental conditions
• Vibration
• Normal use (wear and tear)
• Abuse

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