1. m
SPECIAL Ratnayaka (Assistant Director)
W.M. Wasantha
Sri Lanka Standards Institution, Sri Lanka
Torque Standards
1. Introduction tooling problems before they arise perhaps
Torque is the tendency of a force due to tool wear or broken components.
to rotate an object about an axis, fulcrum, or Also, design studies of torque transducers
pivot. Informally, torque can be thought of are very important in optimization of their
as "rotational force". Torque being a very design for various engineering applications.
important physical parameter, plays a very
vital role in various applications like aviation, 2. Calibration of hand torque
14 automobile, power and agriculture industries. tools
The importance of the torque measurements Hand torque tools are generally
is to control the fastening force on assembly used in the fields of research and
parts and to measure mechanical power. developments, inspections, quality controls
Torque is, generally, measured by as well as servicing where there is a need to
May-June 2012/Vol.14, No.67
mechanical type torque meters/wrenches know correct torque settings. This type of
and these torque tools need to be calibrated tool can also be used in a production
using torque wrench calibration devices. environment to apply torque and check the
Regular calibration of torque tools guarantees tightness of fasteners. The standard guideline
repeated accuracy and traceability to ISO 6789: 2003 specifies the classification,
international standards. Calibration also requirements for calibration, test method and
ensures torque equipment is operating peak marking of hand torque tools.
performance and can highlight potential Also, BS 7882: 2008 specifies
requirements for the calibration and
classification of torque measuring devices,
including those used for the calibration of
hand torque tools to ISO 6789: 2003. The
information to be given on the certificate of
calibration is also listed.
A calibration procedure was
prepared for calibration of hand torque tools
with the help of knowledge acquired during
theoretical and practical sessions and it was
evaluated to check validity to implement in
each participant's country.
Figure 1 - Hand torque tool calibration

2. 3. Calibration of torque
wrench calibration devices
The guideline DKD-R 3-8: 2003
specifies characteristics, calibration,
classification, calibration certificate &
duration of validity of torque wrench
calibration devices. Preparation of the
calibration and calibration procedure were
studied in detail with the help of lectures and
practical sessions.
A torque transducer was calibrated
using a torque transfer wrench as the Figure 2 - Calibration of hand torque tool
standard. Measurement results were calibration devices
evaluated and uncertainty budget was
prepared according to the procedure given calibrated and calibration certificates were
in the DKD-R 8-3: 2003 guideline. A issued for all of them.
calibration procedure was prepared and
evaluated to implement in each participants 5. Conclusion
country to calibrate torque wrench calibration All participants of the torque group 15
devices. were able to completed training programe
May-June 2012/Vol.14, No.67
successfully. The training programme
4. Designing of torque included theoretical and practical sessions.
measuring devices The aim of the theoretical part is to
The lecture series and practical understanding the importance of torque
sessions under the title of "designing of measurements, the mechanism of torque
torque measuring devices" were very tools, classification of torque tools, calculation
important to understand basic principals of of uncertainty budget and calibration
modern torque transducers. certificate. The aim of the experimental part
Basic theory of designing and is to give experiences to participants. The
calculation of torque measuring devices overall aim of the programme, transferring
were studied. According to the calculated the knowledge to the Asia pacific countries,
values, four torque transducers were was achieved successfully.
designed, simulated and verified using the
software "solid work". The alloy steel sensing
body and other accessories were prepared
in a machine shop and strain gauges were
bonded to the sensing body in the practical
sessions. The bridge circuit of the sensing
body was prepared to connect the transducer
to the indicator directly. Finally, cross force
effect of each transducer was analyzed in
order to optimize the design.
All four participants prepared their
own torque transducer. Two of them bending
model with the capacity of 10 N.m and others Figure 3 - Torque transducers designed
are tortional model with the capacity of 500 during the training
N.m. All four torque transducers were