Frequently Asked Questions about Gradient Column Floats

Why do I need gradient column floats?

If you are using a density gradient column to measure the density of plastic, a set of calibrated gradient column floats is essential. To maintain accurate and reliable density measurement, all our floats are delivered with a calibration certificate with ISO 17025 accreditation.

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What does a float look like?

Each float is a hollow glass sphere with a diameter of 5 to 7mm, and a weight of 60 to 250mg. The float’s coloured serial number is fused inside the glass so that you can uniquely distinguish each float. This avoids the need to distinguish floats by imprecise splashes of enamel.

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How are floats packaged?

Each float is packed in its own clip-top plastic tube. If there is more than one float in a set, the plastic tubes will be supplied in a foam filled plastic container.

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What is the recommended frequency of recalibration / re-certification of floats?

As long as floats are looked after carefully, they should have an infinite life, therefore the certificates of calibration do not have expiry dates. Only you will know how important it is to your organisation to have accurate traceable results. Follow the guidance as laid down in your Quality Manual if unsure.

If a float has been dropped, or abraded, or might have suffered any other damage, it should be returned to us for recalibration. Please contact us for prices.

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What is the target turnaround time?

Due to the variability of the ranges required, floats are manufactured and calibrated to order. Our target delivery period is within 6 weeks of the confirmed order.

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How do I distinguish one float from another?

Each float has a coloured serial number fused into the glass. It is not possible to specify what numbers or colours you will receive.

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Can you supply floats outside the density range of 650-2000 kg/m³ at 23°C?

We cannot calibrate floats with a density of less than 690 kg/m³, because there are no liquids lighter than this which are stable at room temperature.

We are able to supply floats with densities greater than 2000 kg/m³, but these are made specially to order, and the calibration is outside our ISO 17025 accreditation.

The maximum float density we are able to supply is 2280 kg/m³.

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Can you supply floats calibrated at temperatures other than 23°C?

Yes. We regularly supply floats to marine biologists calibrated for use in sea water at about 5°C and a few manufacturers measure the density of their composites at 30°C.

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I already have my own floats, can you calibrate them?

We offer calibration of customers’ own floats. Please contact us for more information.

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