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Calibration Beams

Calibration Beams and WeightsNorbar's Test Beams are designed for the static calibration of Torque Transducers. They are ideally suited to Norbar's transducers, but can be employed on other manufacturer's equipment.

Torque is generated by the application of a known force at a known radius from the centre of rotation of the torque transducer.

Designed to remove potential sources of measurement error, these beams can be used to calibrate Norbar torque transducers, and torque transducers from other manufacturers (where design permits), as well as mechanical test devices. UKAS length certification is provided with each beam.

The Beams are designed with square drives machined to the top limit of ISO 2725:1987. This minimises any play between the beam and the transducer. However, a combination of square drive tolerances, misalignment of fittings and elastic rotation of the transducer shaft inevitably cause the beam to rotate from the horizontal under load.

Norbar's Radius Ended Beams are designed with a +/-8% degree usable arc within which the calibration accuracy is unaffected.

Additionally the beams are designed to apply load on a vertical plane which cuts through the square drive inside the transducer. This minimises bending moments on the transducer and, for safe operation, ensures that the beam will not fall out of the transducer.

Gravitational Effects

It is very important that the gravitational value for the Laboratory is established. The effect of not doing this could be a variation in the force produced by the weight of perhaps 0.5% of reading.

It is therefore stronly recommended that you establish the local value of gravity (g)  for your Laboratory and use weights that have been calibrated at that gravitational constant.

The ideal solution is to have the gravity measured on site by the national geological survey agency.

The second best solution is to ask the national agency for a figure calculated from gravitational contour maps.

The third approach is to calculate the value from knowledge of the latitude, and height above sea level in metres. This will give an uncertainty of approximately +/-0.005% but will not reflect local differences due to rock structure etc. Norbar will perform this on request if the above information is provided.

Norbar will supply weights calibrated to gravitational constants specified by the customer. However, if the customer does not specify a value for 'g' they will have been calibrated at an estimated gravitational constant for the customers' location.

Buoyancy Effects

The Norbar system uses calibrated weights to generate a downwards force.

This means that Archimedes principle applies, ie. air pressure under the weights causes an upwards force. This reduces the effective force generated by the weights and therefore the mass must be increased to allow for this.

Under standard conditions (ie. Air density 1.2kg/m3 abd 20 degrees centigrade and working in conventional mass terms) the increase required is by a factor of 0.015%.

Weights purchased from Norbar will already have this factor taken into account.

Weights that are calibrated to standard procedures do not have this factor taken into account because the air buoyancy affects both sides of the mass balance and can be ignored. It is important that weights used for torque transducer calibration are adjusted for air buoyancy.

It should also be noted that the double ended beam design employed by Norbar means that each half of the beam is balanced with regard to buoyancy of the beam. This is a significant advantage over single-arm counterbalanced systems.

 



Beams & Weights

Calibration Disc

  • Calibration Disc & WeightsThe <0.02% uncertainty of applied torque achievable with this disc allows calibration to the highest class of accuracy specified by BS7882:2008.
  • Machined to +/-0.01% (100 microns per meter) from aircraft alloys.
  • Clockwise and counter-clockwise operation.
  • Capable of SI or Imperial calibrations.
  • Compatible with male and female 1/4" square transducer drives.
  • No bearings to cause energy loss during loading.
  • Brass weights with an accuracy better than +/-0.01% are available in five sets to achieve a variety of calibration ranges.
  • Special weight sets can be specified up to a maximum torque of 2.5 N·m.

Radius Ended Beams

  • The <0.02% uncertainty of applied torque achievable with these beams allows calibration to the highest class of accuracy specified by BS7882:2008.
  • Machined to +/-0.01% (100 microns per meter) from aircraft alloys.
  • Radius Ended Calibration BeamClockwise and Counter-clockwise operation.
  • All have interchangeable square drive to increase flexibility of use.
  • Torque radius maintained throughout +/-8 degrees of rotation from horizontal.
  • No bearings to cause energy loss during loading.
  • Balanced to maximise energy transfer to transducer during loading.
  • Loading point offset to reduce bending moments on the transducer.
  • High torque accuracy allows use of cast iron weights rather than stainless steel. Weight accuracy is required to be equal to or better than +/-0.01%.

5000 lbf.ft Calibration Beam

  • The <0.04% uncertainty of applied torque achievable with this beam allows calibration to the high classes of accuracy specified by BS7882:2008.
  • Free Standing Calibration BeamBeam length machined to +/-0.01% (100 microns per meter).
  • Clockwise and Counter-clockwise operation.
  • Beams balanced to maximise energy transfer to transducer during loading.
  • High beam accuracy allows use of cast iron weights rather than stainless steel. Weight accuracy is required to be equal to or better than 0.01%.
  • High quality bearings to reduce energy losses.
  • Gearbox provided to level beam and remove cosine errors.
  • SI and Imperial Calibration possible with one beam (using different weights).


Laboratory Accessories

Norbar can provide various accessories for use with Calibration Beams, these include:

  • Calibration Pedestal - To provide the correct working height for Discs and Beams.
  • Calibration Inclined Bridge - Allows the device being calibrated to be tilted, hence keeping the beam level to within the acceptable +/-8 degree limits.
  • Model 5000 Calibration Fixture - Used in conjunction with a 5000 N·m Static transducer provides an accurate means of calibrating torque multipliers and hydraulic wrenches.
  • Enclosure Meter Plate - When used with a Static Torque Transducer gives an effective means of measuring the torque to remove screw caps from bottles and other containers.


(Obsolete)

Bolt Load Meters

 



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NORBAR TORQUE TOOLS LTD    Beaumont Road, Banbury, Oxfordshire, OX16 1XJ, United Kingdom
Tel + 44 (0) 1295 753600  Enquiries + 44 (0) 1295 270333  Fax + 44 (0) 1295 753643  Email enquiry@norbar.com
Registered Office as above - Registered in England No. 380480 - VAT No. GB 119 1060 05
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