An unbiased flap sampler

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An unbiased flap sampler

• Geoff RobinsonCSIRO Mathematical and Information
  Sciences

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Structure of presentation

• Description of proposed device
• Why it works
• Discussion of features

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Origin of this idea

• First proposed for sampling of hammer-milled
  sugar cane
• Problem that hammer-milled sugar cane will not
  always fall down a vertical chute
• Chute must increase in size from top to bottom
• Other (political) considerations
• Sampling of first expressed juice has probably
  changed in bias with improvements in mills

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How material is divided by continuous operation
of the proposed cutter
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But Gy said flap samplers are always biased ..?

• Always contain a larger part of one side of the
  stream
• These devices are always incorrect and there is
  not remedy
• The remedy is to take a pair of increments with
  complementary biases

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Why is sampler correct?

• Divides whole of continuous stream into discrete
  portions
• Even if motion of flaps is not at uniform speed
• Like a slat conveyor
• Take one portion as a sample

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Practical issues

• Flaps and pathways could be organised differently
• Final pathways for sample could be adjacent
• Final pathways for through could also be
  adjacent
• Take care that ultrafines do not get through
  cracks and end up being over-sampled
• Ensure that dust goes into through most of the
  time

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Good features

• Cheap to construct
• Chutes could be used instead of flaps
• The system does not have to be open to the
  atmosphere
• Easy to maintain

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Disadvantage compared to falling stream cutters
and cross-stream cutters

• Takes larger samples
• Because flaps B and C must only be moved when not
  material is flowing past them
• Thereby increases cost of next sample preparation
  steps
• Need to be able to check that flaps B and C are
  not moved while material is flowing past them

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Choice in practice

• Need a reliable way to change the route travelled
  by the entire stream
• Likely to be useful for sampling alumina?
• Need to be able to handle large amount of
  diverted material and large samples