METTLER TOLEDO is proud to announce the launch of a brand new range of microgram weights with nominal values from 0.05 milligram (mg) to 0.5 mg.

The microgram weights will allow National Measurement Institutes and customers with specialized nanotechnology applications to use the direct comparison method to verify weight values below 1 mg. The weights are available with a calibration certificate so customers can be assured of full traceability to the International Prototype Kilogram. METTLER TOLEDO is the only weights manufacturer in the world to offer calibrated weights with such low nominal values thanks to a joint venture with the British National Measurement Office.

At the extreme end of weights engineering, the nominal values of the weights range from 0.05 mg to 0.5 mg with an astounding level of uncertainty of just 0.0002 mg (0.2 micrograms). The microgram weights are available individually, as well as in a convenient kit containing specially designed accessories and handling tools. The kit provides users with everything they need for calibration of weights and mass verification in the microgram range.

The microgram weights range was developed largely in response to the needs of the nanotechnology market which typically involves the manufacture of objects with dimensions of less than 100 nanometers (smaller than one ten-millionth of a meter), for example computer chips and microscopic devices. The microgram weights have a wide range of applications in the mechanical testing of nano- and bio-material sensors. For instance, they can be used to calibrate the very fine cantilever of an atomic force microscope which is drawn over an uneven object to reveal the surface contours at sub-nanometer level.

When National Measurement Institutes around the world began to indicate the market need for weights below one milligram, METTLER TOLEDO teamed up with John Pain, Calibration Manager from the UK’s National Measurement Office (NMO) in an innovative and ground-breaking project. He stated, “It’s never been done before, there was no blueprint or procedure to copy. We had to develop an effective method to calibrate weights so small that you can hardly see them, along with new methods of calculating uncertainties that would satisfy United Kingdom Accreditation Service (UKAS) requirements.” The calibration method developed involves comparing the weights with the department's mass standards using a combination of subdivision and substitution weighing; the standards being traceable to the national primary standard of mass, KG18, held at the British National Physical Laboratory.

“There were several obstacles to overcome to produce such small weights,” said Michael Greuter, Head of Weights at METTLER TOLEDO, “one was to establish a suitable manufacturing process which would ensure precise and reproducible shapes for each nominal weight.” The microgram weights are bent into the desired shape in an automated process; the smallest nominal weight, 0.05 mg, uses wire with a diameter of just 0.05mm – the width of a human hair. “This was an exciting engineering challenge,” Greuter continued, “but we have perfected the process and each microgram weight is bent into a different shape for clear identification. The microgram weight set includes several special tools for handling the weights – even a miniature draft shield in which to hang the weights for acclimatization prior to use.”

On 18 September, 2012, thanks to the collaborative project with METTLER TOLEDO, the UK’s NMO became the world’s first mass calibration laboratory to be accredited according to ISO 17025 for the calibration of mass standards down to 0.05 mg, with uncertainties as low as 0.0002 mg. The two organizations now work together to offer a combined supply and calibration service to customers worldwide: the microgram weights are produced by METTLER TOLEDO in Switzerland, with calibration and recalibration services performed at the NMO in the UK. John Pain confirmed, “The relationship with METTLER TOLEDO was excellent: when one of the top calibration labs in the world teams up with a world-class manufacturer…the outcome is special.”

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