Guide to Taking a Representative Sample

Chapter 3: Manual stream sampling

3.1 Overview

Sampling must be done in an area where the entire grain stream is accessible. Follow all safety precautions when sampling from a grain stream or near a moving conveyor. Draw samples from the grain stream at regularly timed intervals from the start to the finish of the grain transfer.

This section describes equipment and methods used for manual sampling under these conditions.

3.2 Hand scoops

The hand scoop is a sampling device that consists of a handle constructed of rigid material and a sample collector with a minimum capacity of 50 grams, but less than 200 grams.

The intervals between individual scoop samples must be the same to ensure the samples are representative of the entire lot of grain. The length of interval should take into account:

  • the amount of grain being sampled
  • the size of grain scoop you are using
  • how much sample is needed for grading or testing purposes

The larger the auger being used on farm or the smaller the load of grain, the shorter the interval should be. Using short, consistent intervals and taking many individual scoop samples will make the final composite sample more accurate.

An illustration of acceptable sampling scoops, and a photo of an unacceptable sampling scoop. Text version below.

Sample size is consistent when using any of the cup designs illustrated above.

An illustration of acceptable sampling scoops, and a photo of an unacceptable sampling scoop. Text version below.

Sample size can be variable if using this type of scoop, therefore it’s unsuitable for obtaining a consistent sample size.

Figure 28: Examples of acceptable and unacceptable sampling scoops

Figure 28 - Text version

On an acceptable hand sampling scoop, the sample collector opening has a uniform shape. The shape of the scoop must consistently draw samples of the same size when the scoop is filled to capacity. For example, the scoop opening may be round, square, or rectangular.

A hand sampling scoop is unacceptable if it takes a variable sample size. For example, a scoop shaped like a shovel, with a slanted opening, will draw a variable sample size.

When taking scoop samples:

  • use the same grain scoop to take every sample
  • make sure you take enough samples to fill one 20 L pail to at least three-quarters full

3.3 Methods for stream sampling

  1. Insert the sampling tool into the stream at alternating points across the stream (left, middle, right) for each sampling action.
  2. When sampling from a falling stream (tailgate or hopper bottom), place the scoop into the flow of product upside down.
  3. Rotate the scoop 180 degrees to fill, and then pull the scoop out of the product flow.

Manual sampling over an open pit

When sampling grain over an open pit, be careful to ensure the pit is not “choked.” This can limit the grain’s ability to “free fall” and prevent you from accessing the entire flow of grain.

A photo of good grain flow for sampling during unload, and a photo of poor grain flow choking the pit during unload. Text version below.
A photo of good grain flow for sampling during unload, and a photo of poor grain flow choking the pit during unload. Text version below.

Figure 29: Manual stream sampling over an open pit

Figure 29 - Text version

Grain must be able to flow freely into the pit while the entire conveyance is unloaded. If the grain forms a pile, choking the pit, you may not be able to access the entire flow of grain in order to build a representative sample.

Illustration of correct sampling points during unload. Samples are taken at the right, center, and left points of the grain stream.

Figure 30: Sampling points for manual stream sampling

Manual sampling from a horizontal belt

When sampling a stream of grain from a horizontal belt, insert the scoop into the flow of product upstream and matching the belt speed, and then move it downstream as you turn the scoop to fill with grain. Moving the scoop with the flow allows sampling of the appropriate location on the belt without splashing product or overflowing the scoop.

Illustration of correct sampling points when sampling grain from a horizontal belt. Samples are taken at the right, center, and left points of the grain stream.

Figure 31: Sampling points for sampling grain from a horizontal belt

Photo of a person taking a grain sample from the centre of a horizontal belt.

Figure 32: Sampling grain from a horizontal belt

Manual sampling while loading a grain bin on farm

The best time to make a representative sample of a grain bin is while the bin is being filled. Before you start filling the grain bin, decide how often you’ll take individual scoop samples. Scoop samples must be taken directly from the grain stream using a grain scoop. Take the same number of samples from each truck, if multiple trucks of roughly the same size are filling the same bin.

To make a sample representing the entire contents of a grain bin, you will need a composite sample of each truck filling the bin and four identical pails that hold at least 20 litres, with two labelled A and two labelled B.

Grain from one truck

To build a composite grain sample representing one truckload of grain:

  1. start unloading the grain truck and insert the grain scoop into the grain stream with the cup of the scoop facing down
  2. turn the grain scoop up to catch grain when the scoop is in the correct position
  3. alternate between taking samples from the left, middle and right of the grain stream
  4. continue taking samples at consistent intervals until the truck is finished unloading
  5. place all the scoop samples for the truck in one of the pails labeled A to create a composite sample that represents the entire truckload of grain
Grain from multiple trucks

Large grain bins may be filled by multiple trucks. To prepare a composite sample that represents more than one truckload of grain:

  1. determine how much sample you will need from each truck to fill pail A to three-quarters full
  2. follow the procedure to make a composite sample for each truck
  3. reduce the composite sample from each truck to the desired quantity using the procedure to reduce a composite sample
  4. combine all the reduced samples in one pail labelled A
  5. mix the combined samples in pail A thoroughly by hand

Pail A now contains a composite sample that represents the contents of your entire grain bin.

Representative grain sampling steps

Figure 33: Diagram of representative grain sampling steps

    Figure 33 - text version
    1. Primary samples are taken from throughout the bulk of each truckload of grain going into the bin
    2. The primary samples from each truck are combined to make composite samples representing each truckload of grain
    3. The truck samples are reduced
    4. The reduced samples representing all the truckloads of grain going into the bin are combined
    5. The composite sample represents the contents of the entire grain bin
    6. The composite sample is reduced and sealed in containers labelled to show the bin each sample represents