Hello, I’m Jim Salsbury with Mitutoyo America Corporation and welcome to the
metrology training lab in this episode we're going to continue our discussion
about calibration in a previous episode we discussed that calibration is
critical to maintaining the quality and accuracy of your measuring equipment
but what does that mean what is the real purpose of calibration what makes a
bunch of measurements an official calibration let's use these two common
measuring instruments these outside micrometers and this high accuracy
height gauge called the Mitutoyo linear height in order to understand the
purpose of calibration we will start by looking at the everyday use of the
measuring equipment say this linear height is used daily to measure some
part like this I'll measure on the surface plates here then bring in the
parts and measure this heights whoever is using this measuring system wants to
make sure the overall accuracy and quality of this measurement process
meets their needs now different organizations and different industries
have various quality standards and rules on how to analyze a measurement process
some people talk about gauge repeatability or gauge R&R some talk
about measurement uncertainty but in the end they all have one thing in common
trying to manage sources of air in measurements over time for this linear
height for example the quality of this height measurement depends on many
things like the operator skill the environment that we're in the surface
plate that we're using and of course the linear height gauge
itself and that's where calibration comes in in this case the purpose of
calibration is determine the status of the accuracy of this linear height is it
performing or still performing as accurately as expected is the current
accuracy within stated requirements and specifications and if not what do we do
so when this linear hight or these micrometer 's leave the shop floor and
come in for calibration the first step is to check it out to see if it's
functioning properly to assess what's called the as found or as received
condition this is done before any cleaning before any repair before any
service or adjustments Checking the as-found accuracy is one of the most
critical steps in calibration as it provides the necessary data to
understand the stability or the reliability of the measuring equipment
over time since the last time it was calibrated if the as found data is out
of Tolerance then you have three things you need to do first you need to
determine if that out of Tolerance condition has been impacting your
product quality what does this gauge being out of tolerance today mean for
the measurements that you made just yesterday or a week ago or a month ago
second it de gauges on tolerance maybe your calibration interval needs to be
adjusted to prevent that from happening again
calibration interval should be based on the historical performance of the
measuring instruments and the as found calibration results are the key data
used to lengthen or shorten calibration intervals now third if the gauge is out
of Tolerance what can be done to fix that for some equipment like this
micrometer a good cleaning is often enough to bring it back within tolerance
after the as found data is collected it is typical and calibration to clean
and perform any recommended preventive maintenance after that's done in some
cases like this in digital measured equipment like this linear high cage
there is some kind of maintenance mode that authorized technicians can access
that provide for Corrections or adjustments to be made to the accuracy
of the instruments and in some cases cleaning maintenance adjustments are not
enough and then repair is usually needed in general measuring equipment should
perform within its specification over the lifetime of the equipment that
should be your expectation that at least is definitely our expectation here at
Mitutoyo America except in some very rare cases you should never need to
derate the accuracy of your measuring equipment assuming you've taken proper
care of it and assuming it was well built to start with coming back to the
calibration after any cleaning or adjustments are done the as left
accuracy data is then collected the same accuracy test used for the as found
condition are then repeated to determine the final condition of the measuring
equipments before it's returned back to service a complete calibration includes
the as found readings any necessary cleaning maintenance and adjustments and
then the as left readings
but-but-but-but as we have discussed in Prior episodes of the metrology training
lab just saying calibration does not mean you will get all of that you need
to be careful when contracting calibration services calibration
verification manufacturer's specifications adjustments conformity
assessments you never know what you might get so specify your needs
carefully one important aspect of calibration that we'll cover in a
different episode is the extent of calibration that is needed
for example how many different tests are needed for the number of test points
required to be considered a sufficient calibration this is however a good time
to revisit an important concept that we introduced in a prior episode of the
metrology training lab we discussed what we called user calibrations that are
done on a regular basis as part of the routine use of the measuring equipment
for example on a micrometer the zero point needs to be set on a digital mic
we simply close the measuring faces and press the zero or origin button on a
mechanical micrometer we need to use a wrench to physically rotate the sleeve
to set the zero and on a larger micrometer like this euro to 1 inch mic
we need to introduce a micrometer standard or a gauge block on the linear
height here we have interchangeable probes when each of the different probes
is used or at some other time during the use of it the probe needs to be
calibrated this is usually done with the probe calibration block by measuring
this in different directions we're able to determine or calibrate the probe
diameter all of these user calibrations from setting zero on the mics to
determining the probe diameter on the linear height are very important aspects
of calibration but they're typically not considered part of an official
calibration rather those are covered under proper use of the measuring
equipments however they are very critical to making accurate measurements
and every organization needs a method to manage this properly so I hope you've
learned a few things about the purpose of calibration in this episode thank you
I'm Jim Salsbury and I'll see you next time from the metrology training lab.