Guide for choosing the right Gauge Block Comparator

1. 1
GAUGE BLOCK CALIBRATION
BY
MECHANICAL COMPARISON
(GAUGE BLOCK COMPARATOR)
Arrangement by
Saraswanto Abduljabbar,
Valunteer, specialist and advisor Length Metrology Measurement
1. BACK GROUND
International standard ISO 3650 cover the range of accuracy requirements along
the traceability chain and calibration method is selected according to accuracy require-
ments of the standard and the user. In mechanical comparison methods, the similar
nominal size gauge blocks are compared to each other by suitable probing elements.
Since the compared gauge blocks are in the same nominal sizes, the inductive probes
which have a short measurement range with high accuracy is used in the mechanical
comparison technique, figure 2.
Factors influencing the measurement are: the length calibration of the standard, factors
inherent in the comparator equipment used to measure the length difference such as
scale linearity and reading capability, gauge geometry with respect to its effect on
probing the length difference, the temperature and other environmental factor, etc.
2 Basis of measurement, traceability, reference condition1
2.1 Unit of length: metre
The metre is defined as the length of the path travelled by light in vacuum in 1/299 792
458 of a second (17th General Conference of Weights and Measures, 1983). The
definition is realized by working wavelength standards recommended by the Interna-
tional Committee of Weights and Measures (CIPM).
2.2 Traceability of the length of a gauge block
The measured length of a gauge block is traceable to national or international length
standards, if the measurement result can be related by an unbroken chain of compari-
son measurements each with stated uncertainties to a gauge block which has been
calibrated by interferometry/using appropriate wavelength standards.
1
EN ISO 3650:1998, Geometrical Product Specification (GPS) - Length Standards – Gauge Blocks, Second Edition,
1998-12-15.

2. 2
2.3 Reference temperature and standard pressure.
The nominal length and the measured lengths of a gauge block apply at the reference
temperature of 20 °C (see ISO 1) and the standard pressure 101 325 Pa = 1,013 25
bar2
.
NOTE: The effect on the length of a gauge block caused by deviations from the standard pressure may
be ignored under normal atmospheric conditions.
2.4 Reference orientation of gauge blocks
The length of a gauge block up to and including 100 mm nominal length refers to the
vertical orientation with the measuring faces horizontal. The length of a gauge block
over 100 mm nominal length refers to the horizontal orientation with the block supported
on one of the narrow side faces, without additional stress, by suitable supports each at
a distance of 0.211 times the nominal length from the ends. When such a gauge block
is measured by interferometry in horizontal orientation, the weight of the auxiliary plate
wrung to one of the measuring faces shall be compensated.
2.5 Dimensional stability
The maximum permissible changes in length per year of gauge blocks are stated in
Tabel 1. They apply when the gauge blocks are not exposed to exceptional tempera-
tures, vibrations, shocks, magnetic fields or mechanical forces.
Tabel 1 – Dimensional Stability
Grade Maximum permissible cahnge in length per year
K
0
±(0.02 ߤ݉ + 0.25 × 10ି଺
× ݈௡)
1
2
±(0.05 ߤ݉ + 0.5 × 10ି଺
× ݈௡)
NOTE : ݈௡ is expressed in millimeters
Table 2 – Flatness3
Tolerances ‫ݐ‬௙
Nominal Length, ݈௡
mm
Flatness tolerance, ‫ݐ‬௙
ߤ݉
K 0 1 2
0.5 ≤ ݈௡ ≤ 150 0.05 0.1 0.15 0.25
150 ≤ ݈௡ ≤ 500 0.1 0.15 0.18 0.25
500 ≤ ݈௡ ≤ 1000 0.15 1.18 0.2 0.25
2
ISO 1:1975, Standard reference temperature for industrial length measurements.
3
ISO 1101:—, Geometrical Product Specifications (GPS) — Geometrical tolerancing — Generalities,
definitions, symbols, indication on drawings

3. 3
Table 3 — Limit deviation ‫ݐ‬௘ , of the length at any point of the measuring face from
and tolerance, ‫ݐ‬௩ , for the variation in length.
Nominal
length,
࢒࢔
࢓ ࢓
Calibration grade K Grade 0 Grade 1 Grade 2
limit
deviation
of length
at any
point
from
nominal
length
±࢚ࢋ
ࣆ࢓
tolerance
for the
variation
in length
±࢚࢜
ࣆ࢓
limit
deviation
of length
at any
point
from
nominal
length
±࢚ࢋ
ࣆ࢓
tolerance
for the
variation
in length
±࢚࢜
ࣆ࢓
limit
deviation
of length
at any
point
from
nominal
length
±࢚ࢋ
ࣆ࢓
tolerance
for the
variation
in length
±࢚࢜
ࣆ࢓
limit
deviation
of length
at any
point
from
nominal
length
±࢚ࢋ
ࣆ࢓
tolerance
for the
variation
in length
±࢚࢜
ࣆ࢓
0.5 ≤ ݈௡ ≤ 10
10 ≤ ݈௡ ≤ 25
25 ≤ ݈௡ ≤ 50
50 ≤ ݈௡ ≤ 75
0.2
0.3
0.4
0.5
0.05
0.05
0.06
0.06
0.12
0.14
0.2
0.25
0.1
0.1
0.1
0.12
0.2
0.3
0.4
0.5
0.16
0.16
0.18
0.18
0.45
0.6
0.8
1
0.3
0.3
0.3
0.35
75 ≤ ݈௡ ≤ 100
100 ≤ ݈௡ ≤ 150
150 ≤ ݈௡ ≤ 200
0.6
0.8
1
0.07
0.08
0.09
0.3
0.4
0.5
0.12
0.14
0.16
0.6
0.8
1
0.2
0.2
0.25
1.2
1.6
2
0.35
0.4
0.4
200 ≤ ݈௡ ≤ 250
250 ≤ ݈௡ ≤ 300
300 ≤ ݈௡ ≤ 400
1.2
1.4
1.8
0.1
0.1
0.12
0.6
0.7
0.9
0.16
0.18
0.2
1.2
1.4
1.8
0.25
0.25
0.3
2.4
2.8
3.6
0.45
0.5
0.5
400 ≤ ݈௡ ≤ 500
500 ≤ ݈௡ ≤ 600
600 ≤ ݈௡ ≤ 700
2.2
2.6
3
0.14
0.16
0.18
1.1
1.3
1.5
0.25
0.25
3
2.2
2.6
3
0.35
0.4
0.45
4.4
5
6
0.6
0.7
0.7
700 ≤ ݈௡ ≤ 800
800 ≤ ݈௡ ≤ 900
900 ≤ ݈௡ ≤ 1000
3.4
3.8
4.2
0.2
0.2
0.25
1.7
1.9
2
0.3
0.35
0.4
3.4
3.8
4.2
0.5
0.5
0.6
6.5
7.5
8
0.8
0.9
1
3. Measurement by comparison
3.1 Principle of measurement
In order to determine the length of a gauge block by compa-
rison, the difference of its central length from that of a reference
gauge block is measured and applied algebraically to the length
of the reference. For the probing, the measuring faces of each
gauge are touched from opposite directions as shown in Figure
1, and the length difference is measured by a high resolution
length indicator.
algebraically difference ݈– ݈݊ (see arrow point 1) = ‫ݐ‬௘
݈= Measured length
݈݊ = Nominal length
Fig. 1 Measurement of central length by comparison taking the perpendicular
distance from the centre of a measuring face to the opposite one

4. 4
3.2 Central length
A measurement by comparison transfers the central length of a standard gauge block to
a gauge block under test. The reference gauge block may either directly be measured
by interferometry or related through one or several stages by comparison to a reference
gauge measured by interferometry.
NOTE:
The effect of one wringing, which is included in the length of the reference gauge block
measured by interferometry, is transferred by the comparison measurement.
3.3 Method of determining length by comparison
The relatively small difference in central length between a reference gauge block of
known central length and another gauge of unknown central length is measured by a
high resolution length indicator. (see Figure 2).
Figure 2 — Measurement of central length by comparison taking the perpendicular distance from the
centre of a measuring face to the opposite one. Schematic diagram of a gauge block comparator with
Measured Length Difference
 Reading (ࢊ૚)
 Calibration (ࢊࢉࢇ࢒)
 Drift (ࢊࢍ)
Temperature
 Reading (ࣂ૚)
 Calibration (ࣂࢉࢇ࢒)
 Drift (ࣂ)
࢚ࢋࢌࢌ= 20℃
Penetration
Flatness
࢒࢒࢔
ࢻ
ࣂ࢙
ࢻ
ࣂ
ࢻ = ࢻ࢙
ࣂ = ࢾࣂ + ࣂ࢙
Inductive
Probe 1
Inductive
Probe 2
Parallelism

5. 5
opposing styli and digital readout. The diagram depicts the influence factors in the measurement, and the
mathematical symbols which will represent them in the text.
Figure 2 shows the reference gauge block in the reading position between an upper
contact and one beneath. The anvils are retractable and the weight of the block is
supported independently. The connection line between the two anvils is perpendicular
to the measuring faces. A reading of the indicator is taken at the centre of the reference
gauge block which is then replaced by the gauge block to be measured and a central
reading is taken on it. The vertical position is used for comparison of gauge blocks of
nominal lengths up to 100 mm; Gauge blocks of nominal lengths longer than 100 mm
can also be measured by comparison with a reference gauge block in the horizontal
position. If a vertical orientation as specified in fig.2 is used, the supports are adjusted
horizontally and vertically so that one anvil of the comparator contacts the centre of one
measuring face of the gauge block and the second anvil is moved over the second face
until the minimum reading is obtained.
4. HOW CHOOSING THE RIGHT GAUGE BLOCK COMPARATOR
For mainly economic reasons, most of customers of accredited laboratories prefer their
standards being calibrated by mechanical comparison because of lower costs and
shorter calibration time. In the market there are many products of the Gauge Block
comparators. All of them of course have advantages and disadvantages. This white
paper will guide you how to excecute the right Gauge Block Comparators.
As you know many comparisons, especially those in dimensional metrology, cannot be
done simultaneously. Using a gage block comparator, the standard, control (check
standard) and test block are moved one at a time under the measurement stylus. For
those comparisons each measurement is made at different time. The term calibration
design can be applied to experiments where only differences between nominally equal
objects or groups of objects can be measured.
Ordinarily the order in which these measurements are made is of no consequence. The
usefulness of drift eliminating designs depends on:
1. The stability of the thermal environment, accuracy required in the calibration. The
environment has to be stable enough that the drift is linear.
2. Each measurement must be made in the same amount of time so that the
measurements are made at fairly regular intervals. Finally, the measurements of
each block are spread evenly as possible across the design. The designs are
constructed to:
 Be immune to linear drift.
 Minimize the standard deviations for test blocks (as much as possible)

6. 6
 Spread the measurements on each block throughout the design
 Be completed in 5-10 minutes to keep the drift at the 5 nm level
4.1 Critical contributions to the uncertainty
Critical contributions, which could be dimi-
nished, are temperature deviations, calibra-
tion of the comparator and calibration of
reference gauge blocks. Temperature devi-
ations are influenced by the air temperature
deviations and by radiation of illuminating
bodies and of the operator.
Temperature can not be measured
on the gauge block and therefore table
temperature is assumed to be the tempe-
rature of the gauge block. However, devia-
tions between these two temperatures can differ for up to 0.05°C. Additional problems
appear by longer gauge blocks (near 100 mm) because temperature is not constant
along the height. Beside that, thermal expansion coefficient of gauge blocks is usually
not exactly known. It may differ for 1 ∙ 10ି଺
℃ିଵ
. Thermal expansion correction is
therefore not accurate.
These problem happened because difficult to know what is excactly the CTE4
of
the material gauge block. According to Ted Doiron and John Beers 5
, The uncertainty in
the expansion coefficient of the gauge block is more difficult to estimate.
Table 4: shows that as the blocks get longer, the thermal expansion coefficient becomes systematically
smaller. It also shows that the differences between blocks of the same size can be as large as a few
percent. Because of these variations, it is important to use long length standards as near to 20 ºC as
possible to eliminate uncertainties due to the variation in the expansion coefficient.
4
CTE (Coefficient Thermal Expansion).
5
Gage Block Hand Book, Dimensional Metrology Group Precision Engineering Division, National Institute of
Standards and Technology (NIST-USA).

7. 7
4.2 UNCERTAINTY BUDGET AND CRITICAL CONTRIBUTIONS
In order to establish proper environmental conditions, special microclimatic chamber
with own precise air conditioning system was built in the laboratory. Temperature
deviations in the measuring space of gauge block comparator are limited to 0,1°C.
Temperature is the most important influence factor on measuring uncertainty in
calibration beside the accuracy of calibration of reference gauge blocks. The expanded
uncertainty of the calibration of gauge blocks by mechanical comparison in the machine
is currently (0.03 + L/3000) µm, L in mm*. Using coverage factor k = 2. It was
calculated according to guide ISO GUM 2୬ୢ
edition, 1995 and comprises all important
components. Some of them were evaluated statistically by repeated measurements,
some of them were evaluated by experience and some of them on the basis of different
data from manuals and calibration certificates. All the measurements including tempera-
ture measurements were performed with traceable equipment and measuring uncer-
tainties were evaluated for all measurements.
5. STRATEGY FOR DECREASING CURRENT LEVEL OF
UNCERTAINTY 6
5.1 Study of temperature influences
The following temperature parameters have been analysed:
 change of gauge block temperature after putting it on the comparator,
 temperature difference between the gauge blocks and the comparator table,
 temperature influence of the illumination and the operator, and
 thermal expansion coefficients of gauge blocks.
All the above parameters were detected as critical and are
therefore subject of optimisation. Research was focused into
experimental simulations of different materials and colours of
these materials. It was found out that the radiation of different
materials is quite different and that calibration results are critically
influenced by radiation. The first resource of radiation are lights
producing constant radiation that can be eliminated from calibra-
tion result by calculation. The second source of radiation is the
operator. This source is not constant and is quite critical because
the gauge block that is closer to the operator is heated stronger
that the gauge block standing behind the first one. Shield that is
put between the operator and the comparator is made of
transparent plastics in order to enable the operator to look into measuring area.
6
B. Acko, A. Sostar and A. Gusel, REDUCTION OF UNCERTAINTY IN CALIBRATION OF GAUGE BLOCKS
Laboratory for Production Measurement, Faculty of Mechanical Engineering, University of Maribor, 2000, Maribor,
Slovenia.

8. 8
However, the isolating properties of this material are not good enough to stop the
radiation of a human body.
5.2 Surfaces for thermal stabilisation of the gauge blocks
Surfaces for thermal stabilisation of gauge blocks have a great influence on
thermal behaviour of gauge blocks during the calibration. If these surfaces get other
temperature than the air and the comparator table, the gauge block temperature
changes rapidly. Our analyses have shown that an aluminium plate with bright shining
or light grey surface gives the best results. Long term temperature measurements are
shown in Figure 3 as an example. The white plastic surfaces used before these studies
are always warmer than the air and cause additional heating of gauge blocks. The
same properties have steel surfaces. The stone that has been used in the past has the
worst characteristics and is not recommended at all.
In this research four materials (aluminium, steel, stone and plastic) in four different
colours (black, white, grey and shining) were tested. Temperature was measured in the
air, on the tested surface and on the gauge blocks, that were put on these surfaces.
Long term and short term deviations were measured with the light turned on and with
the light turned off in the measurement room. When the light was turned off, the
differences were not so critical because the radiation was very low. In contrary, when
the lights were turned on, big differences in temperature changes were observed. The
worst behaviour was detected at dark steel and stone surfaces.
Figure 3. Temperature comparison between the aluminium base plate and the gauge
block.
5.3 Material of the comparator table
Some simulations with different materials have shown the importance of the
material and the colour of the table. The existing tables (tested on Mahr and Cary

9. 9
comparators) do not have ideal properties because of dark colours. The temperature is
constantly above the air temperature. When gauge block is put on the table, the
temperature starts to grow and the length of the gauge block is changing.
Typical temperature behaviour after putting gauge block on the table is shown in figure
3. In this case gauge block was put on the comparator table at 10:41 and at 10:50
calibration of this gauge block was finished. From this case we can learn, that the
gauge block should not be measured immediately after putting it on the table. It should
be stabilised for approximately three minutes. Probe 1 in Figure 3 was measuring the
reference gauge block temperature and probe 2 was measuring the temperature of
measured gauge block. We can see that the temperatures of both gauge blocks after
stabilisation are not equal.
5.4 Thermal expansion coefficient of the gauge blocks
Thermal expansion coefficient must be determined with standard uncertainty
‫ݑ‬ ≤ 0.3 ∙ 10ି଺
℃ିଵ
. For this we shall determine thermal expansion coefficient within the
limits of ±0.5 ∙ 10ି଺
℃ିଵ
. Usually this is not a problem, but sometimes we get gauge
blocks without any data about ߙ. In such cases we can not be sure that ߙ was
determined with proper accuracy. Temperature deviations must therefore be dimini-
shed to minimum possible values.
Another problem is the difference between thermal expansion coefficients of the
reference and measured gauge blocks. Uncertainty contribution of his difference in mm
is expressed by the equation:
‫ݑ‬ = ‫ݑ‬(∆ߙ) ∙ ݈௘ ∙ ߠ
Where:
‫ݑ‬ - uncertainty contribution in mm
‫)ߙ∆(ݑ‬ - uncertainty of the difference of thermal expansion coefficients (݅݊°‫ܥ‬ିଵ
)
∙ ݈݁ - nominal length of gauge blocks
ߠ - maximum possible temperature deviation
If uncertainty of the difference between thermal expansion coefficients is 0.6 × 10ି଺
℃ିଵ
and maximum possible temperature deviation is 0.1°C, than the uncertainty contribution
in calibration of 100 mm gauge block is 0.006 µm what is the maximum possible limit for
our demands. If temperature deviation is 0.3°C, we get the value of 0.018 µm, what is
far too much.
From the above example we can conclude that temperature deviations and the
limits of determination of thermal expansion coefficient must be within very low values.
These two components are in strong correlation and influence the length dependent
part of the combined uncertainty.

10. 10
Figure 4. Thermal behaviour of gauge blocks after putting them on the comparator
table
5.5 Indentation of different gauge blocks by the applied measuring force
Research in this field is made in order to be able to calibrate gauge blocks of
different materials. The indentation is calculated by the following (Roark's) equation:
݅= 1.4 ∙ ඨ
‫ܨ‬ଶ ∙ ‫ܥ‬ா
ଶ
݀
య
‫ܥ‬ா =
1 − ‫ݒ‬ଵ
ଶ
‫ܧ‬ଵ
+
1 − ‫ݒ‬ଶ
ଶ
‫ܧ‬ଶ
Where:
݅ - indentation
‫ܨ‬ - probing force
݀ - probing ball diameter
‫ݒ‬ଵ - Poisson number of the probing ball material
‫ݒ‬ଶ - Poisson number of the gauge block material
‫ܧ‬ଵ - elasticity module of the probing ball material
‫ܧ‬ଶ - elasticity module of the gauge block material
If probing force is 0,1 N, probing ball of d = 2 mm is made of hart metal and gauge block
is made of steel, than the indentation is 0.116 µm. For the gauge block made of hart

11. 11
metal this value would be 0.081 µm. The difference of the both indentations is 0.035
µm. The greatest problem in this calculations is to get right values for ‫ܧ‬and ‫.ݒ‬ Every
deviation of these values causes uncertainty of indentation calculation. The second
problem is evaluation of probing force, which shall be measured very precisely. There-
fore, some experimental work has already been performed in order to evaluate uncer-
tainty of indentation. It was found out that the standard uncertainty can be held in the
limits of 0.008 μm.
6. DRIFT ELIMINATING DESIGN
The sources of variation in measurements are numerous. Measurements on gauge
blocks are subject to drift from heat built-up in the comparator. This effect cannot be
minimized by additional measurement because it is not generally pseudorandom, but a
nearly monotonic shift in the readings. In dimensional work the most important cause of
drift is thermal changes in the equipment during the test.
The purpose of drift eliminating design is remove the effects of linear instrumental drift,
but also alowing the measurement of the linear drift itself. This measured drift can be
used as a process control parameter. For small drift rates an assumption of linear drift
will certainly be adequate. But, for high drift rates or long measurements time the
assumption of linear drift may not be true.
Measurements on gauge blocks are subject to drift from heat build-up in the compa-
rator. This drift must be accounted for in the calibration experiment or the lengths
assigned to the blocks will be contaminated by the drift term. The designs are
constructed so that the solutions are immune to linear drift if the measurements are
equally spaced over time. The size of the drift is the average of the ݊ difference
measurements. Keeping track of drift from design to design is useful because a marked
change from its usual range of values may indicate a problem with the measurement
system.
7. OVERVIEW OF THE GAUGE BLOCK COMPARATOR PRECIMAR 826 VS
TESA UPG.
PRECIMAR 826 TESA UPD TESA UPC
DESIGN: rigid cast-iron stand with vertical
guide
rigid cast-iron stand with vertical
guide
Measuring range 0.5 mm to 170 mm 0.5 mm up to 100 mm
Weight 37 Kg (comparator only) 23 kg (comparator only)
NOTE:
Heavier Unit more steady (immune from vibration)
Repeatability (with no influence
of external temperature)
± 0.01 µm 0.04 µm
Measuring uncertainty (૙. ૙૜ + ࡸ/૜૙૙૙) μ࢓ , ࡸ ࢏࢔ ࢓ ࢓ ࢁ = ± (૙. ૙ૠ + ૙. ૞ ∙ ࡸ) μ࢓
For instance Gauge Block 100 For instance Gauge Block 100

12. 12
mm, ‫ݑ‬ = (0.03 + 100/3000) μ݉
= 0.03 + 0.033
= 0.063 μ݉
mm, ‫ݑ‬ = (0.07 + 0.5 ∙ 0.1) μ݉
= 0.07 + 0.05
= ૙. ૚૛ μ࢓
NOTE:
Following the hierarchy of calibration, calibrator must be 10% or 20% smaller then tolerance of the
working standard. For example, Gauge Block tolerance 0.12 µm (Grade 0, length 100 mm), must be
calibrated by Gauge Block Comparator with Uncertainty minimum 0.12 x 0.2 = 0.024 µm. Following this
reason, methode direct measurement is not acceptable. In the comparison method the stability of the
instrument is 0.02 + 0.25 ∙ 10ି଺
μ݉ ( Precimar 826).
Repeatability (with no influence
of external temperature)
± 0.01 µm 0.025 µm
Measuring uncertainty (૙. ૙૜ + ࡸ/૜૙૙૙) μ࢓ , ࡸ ࢏࢔ ࢓ ࢓ ࢁ = ± (૙. ૙૞ + ૙. ૞ ∙ ࡸ) μ࢓
For instance Gauge Block 100
mm, ‫ݑ‬ = (0.03 + 100/3000) μ݉
= 0.03 + 0.033
= 0.063 μ݉
For instance Gauge Block 100
mm, ‫ݑ‬ = (0.05 + 0.5 ∙ 0.1) μ݉
= 0.05 + 0.05
= ૙. ૚૙ μ࢓
Repeatability (with no influence
of external temperature)
± 0.01 µm 0.015 µm
Measuring uncertainty (૙. ૙૜ + ࡸ/૜૙૙૙) μ࢓ , ࡸ ࢏࢔ ࢓ ࢓ ࢁ = ± (૙. ૙૛ + ૙. ૛ ∙ ࡸ) μ࢓
For instance Gauge Block 100
mm, ‫ݑ‬ = (0.03 + 100/3000) μ݉
= 0.03 + 0.033
= ૙. ૙૟૜ μ࢓
For instance Gauge Block 100
mm, ‫ݑ‬ = (0.02 + 0.2 ∙ 0.1) μ݉
= 0.02 + 0.02
= ૙. ૙૝ μ࢓
NOTE:
Following the Gauge Block tolerance in the Table 3, UPC and UPD can calibrate Gauge Block Grade 1
and 2 only. Precimar 826 can calibrate Gauge Block Grade 0, 1 and 2. Only TESA with
ܷ= ± (0.02 + 0.2 ∙ ‫)ܮ‬ μ݉ can be used for Grade 0, but this instrument still struggle to get the uncertainty
because it will depends on the temperature correction. You know that in the paragraph 4.1 explained
Thermal expansion correction is therefore not accurate. So that is why the Comparator need the deviation
of the temperatur is 0.03ºC.
Material Housing Diecast Iron Diecast Aluminum
Sensors for length dimensions:
 Double Probes Yes Yes Yes
NOTE:
The measuring configuration consisting of two probes aligned opposite one another combined with the
concept and quality of the measuring system is the guarantee for an extra low measurement uncertainty.
 With analog and digital
indication system,
Yes Digital Only Analog Only
 Measuring force activation
 Measuring bolt retraction
Yes
By electrical vacuum pum lifted
Yes
By Vacuum
Yes
By electro-
motorised
Measurement Method Comparative Measurement Direct
Measurement
Comparative
Measurement
Advantage:
Enhances the measuring condi-
tions, thus permitting all measure-
ments to be taken with lower
uncertainty. NO linear error.
Disadvantages:
Allows gauge blocks of same
nominal lengths to be measured
by comparison. Need 122 Gauge
Block set as a standard compa-
rator.
Advantage:
Permits over 90 % of a 122-piece
set to be checked using the same
reference gauge block All nominal
lengths of the full gauge set being
contained within 0,5 and 25 mm.
Disadvantages:
In fact the measuring span is
therefore exceeded, caused of
Linear Error of the probes.
NOTE:
For the Direct measurement method actually data will found linear error that is not an advantages for the
machine due to the machine must immune to linear drift. So the choice of the Comparative methode is the
best solution.

13. 13
PRECIMAR 826 TESA UPD TESA UPD
Computer-aided calibration
• Measurement of single gage blocks
• Measurement of complete gage
block sets
• Simultaneous calibration of several
equal gage block sets.
Yes
Yes
Yes
Yes
Yes
Yes
Features of the Hardware:
• Selection and determination of
measuring sequences.
Yes Yes
• Management of testpiece and
standard gauge block sets.
Yes Yes
• Management of individual gauge
blocks
Yes Yes
• Measuring program to perform gauge
block tests
Yes Yes
• Control of all operations and inputs Yes Yes
• Automatically assigning the sequence
of nominal dimensions for set tests
Yes Yes
• Organization of the measurement
process for testing multiple sets
Yes Yes
• Printer program for test records and
for the printout of standard gage block
sets
Yes Yes
• Data management Yes Yes
ADVANTAGES:
• Rigid cast-iron stand, making the
unit temperature stable
Yes Yes
• Easily adjustable vertical slide with
upper probe
Yes Yes
• Fine adjustment via rigidly
Connected Parallelogram springs
Yes No
NOTE:
Fine adjustment is carried out by adjusting a rigidly connected spring parallelogram system which is
integrated into the support arm.
• Electro pneumatic lifting Yes Yes
• Gentle, precise and extremely smooth
manipulator operation due to slideways,
which are impervious to dirt
Yes Yes
NOTE:
The foot of the base holds the manipulator for correctly positioning the gage blocks. Smooth movement is
ensured by high precision ball bush guides.
• Ergonomical operation due to the
optimally arranged gauge block
manipulator
Yes Yes
NOTE:
Whenever the gage blocks are moved, the inductive probes are lifted by means of an electrical vacuum
pump.
• Measurement not influenced by
manual force
Yes Yes
• Easy movement of the gage blocks
due to support consisting of
hardened circular guide bars
Yes Yes
• No zero setting required, since the
set value is automatically related to
the nominal value of the respective
reference gage block
Yes Yes
• Very effective protection from heat Yes Yes

14. 14
due to an acrylic glass screen along
the front and both sides of the unit
• Penetration correction Yes NO
NOTE:
See paragraph 5.5, the correction of the geometric factor of the probe tip penetration.
• Correction of differing thermal
expansion coefficients
Yes Yes
• Computation of mean values Yes Yes
• Simultaneous calibration of several
sets possible
Yes Yes
• Inherent stabilization of temperature
and vibration
Yes Yes
CONCLUTION:
All the concept of the Comparator must be supported for the its accuracy, with the
requirement of the uncertainty measurement factors, such as:
1. The design, must be immune from the errors, such as measuring base by refelcted
material to reduce temperature influence.
2. Comparation method, to avoid linear error of the probes.
3. Quick measurement to avoid linear drift cause of time of measurement.
4. Avoid themperature correction due to difference of the CTE, unless the themperature
difference over 0.4ºC.
5. Correction from the elasticity of the material effect from the contact point.
References:
1. ISO 3650:1999, Geometrical Product Specifications (GPS) — Length standards —
Gauge blocks.
2. ISO. GUM: 1995, Guide Uncertainty of Measurement.
3. Ted Doiron and John Beers, Gage Block HandBook, Dimensional Metrology Group
Precision Engineering Division National Institute of Standards and Technology.
4. B. Acko, A. Sostar and A. Gusel, reduction of uncertainty in
calibration of gauge blocks, Laboratory for Production Measurement Faculty of
Mechanical Engineering University of Maribor, 2000 Maribor, Slovenia.