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The new 20 kN·m Torque Standard machine at NMISA Presenter: James Matosse 2018 Test and Measurement Conference
The new 20 kN·m Torque Standard machine at
NMISA
Presenter: James Matosse
2018 Test and Measurement Conference
Overview
• Background
• NMISA torque rigs
• The new 20 kN·m torque standard machine at NMISA
• Machine performance evaluation
• Conclusion
Background
The South African industries require torque traceability through the calibration of torque tools and sensors, to ensure quality control and international trade in different applications. Such as;
• The automotive manufacturing:- torque transducers in process control, calibration and checking of fuel efficiency systems and power assisted steering.
• Seal protection, factories and workshops:- torque tools applications, e.g. ensuring that suitable torques are exerted on bolts and nuts in the assembly of mechanical parts.
• Safety:- even the “tightness” of food, beverage and medicine lids depends on the measurement of torque.
Background
• The NMISA has, in the past, been able to provide traceability in the calibration of square drive torque transducers in the range;• 1 N·m to 1000 N·m
• This meant traceability above 1000 N·m had to be sourced from other NMIs outside South Africa resulting in excessive cost and lengthy downtime.
• NMISA is currently establishing a new national torque standard for the calibration of torque transducers up to 20 kN·m to meet the torque industry requirement in SA.
NMISA torque rigs
The structural design type of a calibration machine determines the method of calibration: the use of lever and mass (m·g·l) system or the comparison method.
NMISA torque rigs
• The limitations of that design:• The measurement range is limited to 1 kN·m due to the size and
loading capacity of the beam.
• The weights have to be manually loaded, resulting in hysteresis errors.
• The rigs only accommodate square drive transducers.
• Parasitic forces due to transducer misalignment result in high measurement uncertainties
• Industry calibration requirements are uncertainties less than ± 0,1% whereas the rig CMC is around ± 0,5%.
• Design modifications are being implemented to rectify the above limitations and for “Overlap checks” with traceability to national standard of mass.
The new 20 kN·m torque standard machine at NMISA
The machine uses the comparison method to calibrate torque transducers with the following main components
• Drive system (gearbox and servo motor)• Used to generate torque to both the UUT and reference transducer
• Hydraulic clamp• The ETP Techno type is used as the counter bearing for the reaction
torque on the machine main frame
• Flexible couplings• The machine uses two flexible couplings to reduce the effects of
side forces and bending moments as a result of eccentric mounting
The Machine
The new 20 kN·m torque standard machine at NMISA
• A set of high accuracy torque transducers are used as reference standards to cover the full range of the 20 kN·m torque standard machine. They are TB2 flange type transducers with capacities of 500 N·m, 3 kN·m and 10 kN·m calibrated to their 100% overange.
• The height adjust mechanism is used to allow the machine to accommodate various sizes of torque transducers.
• The machine has a computer data capture program and a manual control for the speed and direction (clockwise or anti-clockwise) of the generated torque, with the capability for automation in the near future.
• A measuring amplifier (model: HBM MGCplus) is connected to the reference transducer and used to display the applied standard torque.
• Different types of torque transducers such as flange, square drive and smooth shaft can be calibrated using this machine.
Machine performance evaluation
• Sets of torque transducers used as references and intermediate check standards in the 20 kN·mtorque standard machine were each calibrated at PTB in Germany.
• These same sets were again calibrated using the 20 kN·m torque standard machine at NMISA.
• The measurements were performed following the calibration procedure DIN 51309:2005-12 by both NMIs
• The measurement results were compared using the Normalised Error, designated as 𝐸𝑛.
Machine performance evaluation
𝐸𝑛 =𝑥𝑙𝑎𝑏 − 𝑥𝑟𝑒𝑓
𝑈𝑙𝑎𝑏2 + 𝑈𝑟𝑒𝑓
2
Where:
• 𝑥𝑟𝑒𝑓 = Measurement result from PTB.
• 𝑥𝑙𝑎𝑏= Measurement result from NMISA.
• 𝑈𝑙𝑎𝑏= Expanded Uncertainty of Measurement, NMISA.
• 𝑈𝑟𝑒𝑓= Expanded Uncertainty of Measurement, PTB.
Machine performance evaluation
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0,10
0,20
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0,60
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0,90
1,00
10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
No
rm
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sed
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Applied torque(%)
Normalised error (En) values calculated from calibration results of reference torque
transudcers calibrated at PTB and NMISA.
En (clockwise) 20 kN.m
En (anticlockwise) 20 kN.m
En(clockwise) 5 kN.m
En (anticlockwise) 5 kN.m
En (anticlockwise) 1 kN.m
En(clockwise) 1 kN.m
Machine performance evaluation
• From the graph, it can be observed that the En value is less than 1 across the entire range for all three torque transducers in both directions (clockwise and anticlockwise).
• The result En < 1 indicates good agreement or equivalence between calibration results obtained by PTB using their standard torque machine and NMISA using its new 20 kN·m torque standard machine.
• NMISA is aiming to claim CMC of 0.05% or lower in the entire measuring range (100 N·m - 20 kN·m) of the machine.
In conclusion
• The 20 kN·m torque standard machine at NMISA is capable of meeting the current need of torque traceability in South Africa.
• An industry study has been conducted to document the various types and models of torque transducers in need of calibration.
• The NMISA torque laboratory plans to start with calibrations in the early part of the 2019 calendar year and aims to obtain full accreditation status by the year 2020.
The Team
Installation
Torque rig display
