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Linear Samplers
CMP Toronto
Hockey Hall of Fame
Sept. 10, 2015.
Probabilistic vs. Non-probabilistic Sampling
The problem of using non-probabilistic in-stream probes is that they can be biased negatively one day, be accurate the next, and positively biased a week later. This means an assumption that the process stream is homogeneous must be made, which is difficult. The amount of sampling error that is introduced depends on varying characteristics of the stream; the flow rate, the pressure, velocity, SG of slurry, viscosity and piping layout.
Why does bias happen with non-probabilistic samplers? If there are the slightest differences in the slurry entering the sample volume due to stream characteristics, then the sample volume will be different than the average of the whole stream. Additionally, even if a totally turbulent state could be artificially created in the flow just before the sampling point, the introduction of an obstacle would re-structure the flow in an unpredictable manner.
- Properly designed cutter to collect top to bottom cross-section of the stream
- Replaceable one piece non-adjustable cutter cap
- Non-restrict slurry flow from cutter discharge
- Top-mounted cutter for easier maintenance
- Inspection door to access cutter and cutter cap
Model TMCF
Top-Mounted Cutter Sampler with Mixing Flume ahead of fixed cutter. Encourage the slurry to be well mixed before a cross sectional cut is taken.
Probabilistic Sampling
Model 1330 Linear Sampler with Integrated Cutter Enclosure – 1330/ICE™
- Properly engineered sampling station where every particle has equal opportunity to be included in the sample, independent of stream characteristics
- Linear moving cross-stream cutter takes a proportional section of the whole stream
- Inlet velocity can be controlled with inlet launder
- Proper orientation of cutter to stream trajectory
- Linear sampler mechanism protected from splashing of stream
- Slurry trajectory contained in enclosure minimizes splashing
- Complete sample increment discharges through the sample pipe and is contained in a sample launder
- Sample launder protects the integrity of the sample since no contamination of the sample occurs
- Customize to the process layout
- Optional water nozzles for cleaning the cutter and launder after sample interval
- Available with horizontal discharge as shown or vertical discharge or open bottom as layout requires
In conclusion, Heath & Sherwood has experience with customer applications where non-probabilistic sampling stations, such as pressure pipe probes and even in-line gravity cutters, have to be replaced with a probabilistic linear moving cross-stream cutter station due to the lack of sampling accuracy.
Reference
1) Pitard F. Francis - Pierre Gy’s Sampling
Theory and Sampling Practice – 2nd Edition -
The Delimitation Error page 243 14.5.2.
Taking Part of the Stream All of the Time
