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Realization of Torque

Working Group 1.22

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The Working group 1.22 is responsible for the realization of the physical quantity of torque. The torque is defined as the product of an acting force and its perpendicular distance to the centre of rotation considered. Therefore the unit of the torque is derived from the unit of the force (the Newton N) and that of the length (the Meter m). The Newton itself is traced back to the basic units of the International System of Units (SI) Kilogram, Meter and Second.

Two cases of the torque measurement can be treated: a 'pure' torque (generated by a force couple, application in torque transducers) and a torque with superimposed cross forces and bending moments (generated by a single force, application in torque wrenches). In addition, a subdivision into static (quasi constant torques with or without rotation) and dynamic (varying with time) torques must be made.

The field of activity ranges from fundamental metrological research, the development of standard machines to the calibration of transducers and consultation. Another application is the measurement of the rotational power in medical ergometers, which are traced back to the erometers standard in the torque working group.

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Research/Development

Realization of the unit of torque with torque standard machines

Torque standard machines are the primary national standards for the physical quantity of torque. The unit of torque - the Newtonmeter - is realized in these machines for static use with discrete values in the range from 1 mN·m up to 20 kN·m and continuously with larger uncertainties up to 1 MN·m. The metrological foundations of the realization of the torque are investigated, new principles are developed and used in measuring devices.

Development and investigation of calibration machines operating with the comparison method

Two calibration machines (measuring ranges: 0,01 N·m to 20 N·m and 1 N·m to 5 kN·m) are in operation for investigating the influence of the measuring procedure on the uncertainty of measurements using the comparison method. The application fields range from hand-operated torque tools to torque wrenches and torque transducers.

Traceable calibration of ergometer test stands

According to the Medical Devices Act, foot pedal ergometers are considered as "medical devices with a measurement function". The rotational power provided by the patient is measured as a product of momentary rotation speed and acting torque. The standard to which all calibrated ergometers are finally traced back is operated by the Working Group.

Comparison measurements / calibrations

Intercomparison measurements are carried out with transfer standards in the measuring range from 1 mN·m up to 1 MN·m. Reference standards from calibration laboratories are compared and their smallest uncertainties of measurement are defined. Reference torque wrenches as well as torque measuring instruments for controlling less accurate calibration facilities are calibrated.

Torque transfer standards and multicomponent transducers

Transfer standards with known metrological properties, especially concerning its short- and long-term stability, are used for the dissemination of the unit of torque; by the help of multicomponent transducers it is possible to measure in calibration machines acting mechanical disturbing components which could influence the calibration of torque transducers.

Co-operation in national and international standardization of calibration methods

The standardization is neccesary to guarantee the uniformity of the testing methods and the comparability and equivalence of measuring results obtained in different machines.

Co-operation with the German Accreditation Body (DAkkS)

During the accreditation of calibration laboratories by the German Accreditation Body (DAkkS) expert opinion is given. Torque laboratories of industrial enterprises and material testing institutions get technical consultation and support with measuring instrumentation within the comittee "Torque" of the German Calibration Service (DKD).

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Services

Calibration of torque transducers and comparison measurements

The transfer of the torque scale to laboratories in research and industry is ensured by the calibration of torque measuring devices and by comparisons with torque calibration machines.

Assessment of calibration laboratories for torque by order of the German Accreditation Body

The assessment of calibration laboratories is carried out by order of the German Accreditation Body (DAkkS).

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Information

1 N·m Torque Standard Machine

Short name 1-N·m-Dm-NME
Principle deadweight
Rel. exp. (k=2) uncertainty 1·10-4 (Range: 0.1 N·m to 1 N·m)
2·10-4 (Range: 0.01 N·m to < 0.1 N·m)
1·10-3 (Range: 0.001 N·m to < 0.01 N·m)
Torque steps

1 mN·m, 2 mN·m, ..., 10 mN·m
10 mN·m, 20 mN·m, ..., 100 mN·m
20 mN·m, 40 mN·m, ..., 200 mN·m
50 mN·m, 100 mN·m, ..., 500 mN·m
100 mN·m, 200 mN·m, ..., 1000 mN·m

Remarks By combining different steps for clockwise and anti-clockwise torque, an additional step-down to a ratio 1:100 is possible.

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1 kN·m Torque Standard Machine

Short name 1-kN·m-Dm-NME
Principle deadweight
Rel. exp. (k=2) uncertainty 2·10-5
Torque steps 1, 2, ... , 10 N·m
2, 4, ..., 20 N·m
5, 10, ..., 50 N·m
10, 20, ..., 100 N·m
20, 40, ..., 200 N·m
50, 100, ..., 500 N·m
100, 200, ..., 1000 N·m
Remarks By combining different steps for clockwise and anti-clockwise torque, an additional step-down to a ratio 1:100 is possible.

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20 kN·m Torque Standard Machine

Short name 20-kN·m-Dm-NME
Principle deadweight
Rel. exp. (k=2) uncertainty 2·10-5
Torque steps 100 N·m to 20 kN·m in 100 N·m steps
Remarks By combining different steps for clockwise and anti-clockwise torque, an additional step-down to a ratio 1:100 is possible.

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220 kN·m and 1.1 MN·m Torque Standard Machines

Short name 1.1-MN·m-Dm-NME
Principle force couple measurement
Rel. exp. (k=2) uncertainty 1·10-3
(Range 200 kN·m: 4 kN·m to 20 kN·m and
Range 1 MN·m: 20 kN·m to 100 kN·m)
8·10-4
(Range 200 kN·m: 20 kN·m to 200 kN·m and
Range 1 MN·m: 100 kN·m to 1000 kN·m)
Torque steps 220 kN·m measuring range:
continuously in the range from 4 kN·m up to 220 kN·m
1.1 MN·m measuring range:
continuously in the range from 20 kN·m up to 1.1 MN·m
Remarks

The forces acting on the two-armed lever are measured by means of force transducers. The machine has a vertical measuring axis.
Further informationen about  special features of the machine:
Opens internal link in current windowAdaptation conditions and calibration procedures

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20 N·m Torque Calibration Machine

Short name 20-N·m-Dm-KE
Principle torque reference transducer
Rel. exp. (k=2) uncertainty 2·10-4 (Range: 0.1 N·m to 20 N·m)
2·10-3 (Range: 1 mN·m to 0.1 N·m)
Torque steps Continuously in the ranges from 1 mN·m up to 0.1 N·m and 0.1 N·m up to 20 N·m
Remarks Calibration machine with reference transducer for automatic continuous measurements.

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2 kN·m Torque Calibration Machine

Short name 2-kN·m-Dm-KE
Principle torque reference transducer
Rel. exp. (k=2) uncertainty 2·10-4
Torque steps Continuously in the range from 1 N·m up to 2 kN·m
Remarks Calibration machine with reference transducer for automatic continuous measurements.

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5 kN·m Torque Calibration Machine

Short name 5-kN·m-Dm-KE
Principle torque reference transducer
Rel. exp. (k=2) uncertainty 2·10-4
Torque steps Continuously in the range from 100 N·m up to 5 kN·m
Remarks Calibration machine with reference transducer for automatic continuous measurements.

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1000 W Rotary Power Measurement

Short name dyncal100
Nominal power 1000 W
Rel. exp. (k=2) uncertainty 2·10-3 (absolute 0,2 W)
Modes of operation turning speed range (5 ≤ n ≤ 150) min-1
power range (5 ≤ P ≤ 1000) W
maximum torque 100 N·m
- driving mode:
max. control deviation of turning speed 0,1% (absolute 0,1 min-1)
- breaking mode:
max. control deviation of power 1% (absolute 1 W)
Remarks device for the calibration of ergometer test stands

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Adaptation recommendations

nominal torque shaft diameter shaft length
Mnom Da La
N·m mm mm
<= 20 15h7 >= 40
> 20 to <= 100 20h7 >= 45
> 100 to <= 500 30h7 >= 60
> 500 to <= 2000 50h7 >= 80
> 2000 to <= 5000 70h7 >= 110
> 5000 to <= 20000 110h7 or
130h7
>= 120
>= 150

If the design with a hub is selected, depending on the material used, the following minimum wall thicknesses shall be complied with (Dn - outside hub diameter):

material steel grey cast iron aluminium
Dn / Di 1.5 2.0 2.5

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1.1 MN·m Torque standard machine

On both sides, a flange adaptation using groove stones in circular ring grooves with the following parameters is specified:

diameter of circular ring groove in mm 500 700 900
maximum torque in kN·m ≤ 350 ≤ 700 > 700
maximum number of screws M36 (12.9) 23 30 30

 

The calibration object must be supplied in such a way that all the components and adaptors are, as far as possible, pre-assembled. Should this not be possible for certain reasons, this must be agreed with PTB. The technical responsibility for the torque transducer provided with adaptors lies, in any case, with the customer (please refer to the "General Terms and Conditions of Business" of PTB (AGB), Section 10.3).

The geometry of the adaptor flange plates must be agreed with PTB, as well as all screwings – in particular, if screws are used which are different from those which are provided on the facility by default. As standard, screws in accordance with ISO 4762 (DIN 912), thread size M 36 (12.9), lengths 90 mm and 120 mm, have been defined. The maximum useable thread depth in the T-slides is 60 mm.

To be able to effect the screwing, a minimum distance of 150 mm must be complied with between opposite screw heads (or between screw heads and opposite body edges).

To guarantee centering on the side of the machine, central fitting bores with Ø = 20 H7 mm, depth ≥ 20 mm are to be provided ideally at the respective adaptor flange surfaces.

Further information on the calibration object, including adaptations:
- maximum mass*: 2000 kg
- maximum diameter*: 1000 mm
- minimum height*: 600 mm
- maximum height*: 2200 mm
*) Deviations from these measures must be agreed with PTB for each individual case.

Conditions for electric connection
It is, as a matter of principle, possible to record the measurement signal of the torque transducer to be calibrated if the transducer has a 6-conductor connection, if it requires a supply voltage of 5 V, and if the connection cable supplied together with the transducer has a sub-D-connection on the side of the amplifier which shows an assignment in accordance with HBM standard. Other variants must be agreed with the working group. Also the calibration of complete measuring chains is possible if this has been agreed.

Calibration process
The calibration is carried out in accordance with DIN 51309: 2005-12 or EURAMET/cg-14, respectively. If deviations or additional special services are desired such as, for example, adjustment work on the measurement system, these must be agreed and coordinated with the working group in advance. Please refer to the heading "Other information" in our form under Opens external link in new windowWeb form for calibration requests where these requests can be filled in. The contact data of the members of the working group "Torque" are to be found under Contact persons.

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