Grain sampling systems
April 1, 2007
Kevin B. Mason
The following article is the first in a two-part series on grain sampling systems. The first part focuses on probe samplers used for sampling trucks and railcars. The second article, which will appear in an upcoming issue of World Grain, will examine cross-cut and point type grain samplers.
Quality and quantity are typically key considerations in any commercial grain commodity transaction. Quantity can be easily determined by measuring or weighing the lot of product, but gauging the quality is more difficult since it is not practical to inspect the entire lot.
It is therefore critical that a representative sample be used to allow a reasonably accurate assessment of the quality of the entire lot. When it comes to grain quality, storage and handling facilities are primarily concerned with the characteristics and consistency of grain kernels themselves, as well as the presence and proportion of any contaminants.
The most common types of sampling equipment used in the grain industry today are probe samplers, cross-cut samplers and point samplers. This article will examine probe samplers, which are primarily used for sampling trucks or railcars.
Probe samplers can be manual or mechanized. Manual hand probes are typically used for sampling bins and sometimes for sampling trucks and rail cars. They usually are compartment type probes with an inner and outer tube that are utilized by inserting the probe, rotating it to take the sample, rotating it again to close the probe, and withdrawing it from the grain.
Mechanized probes are commonly used to sample incoming trucks and can be purchased in two styles: core and compartment. Compartment probes are similar to manual hand probes in that they are constructed from dual slotted rotating tubes, with the addition of a pneumatic conveying mechanism. Operation is similar to that of a manual probe.
Core probes are much simpler, consisting of dual concentric tube construction. As the probe is forced into the grain mass, grain enters the central tube. As this occurs, air is drawn out of the top of the center tube while approximately the same amount of air flows into the outer tube and is directed into the bottom of the center core, helping to carry the core of grain up and replacing the air drawn out of the center tube.
The simplicity, low maintenance and good sample performance of core style probes means they are generally the preferred probe style.
The installation of a truck probe is typically driven by the improvement it makes in receiving capacity. A truck probe will improve the speed and efficiency of receiving at a busy elevator by allowing the grain to be graded and the destination bin decided before the truck is dumped, thereby maximizing usage of the receiving equipment.
Most truck probes are hydraulic, al- though light-duty models are available with electric drives. Your choice of probe should focus largely on manufacturer preference and design quality, as well as expected truck volume.
Installation of truck probes is usually straightforward and involves following the manufacturer’s instructions. Care must be taken to install the probe at the proper height so it can reach over the edge of the truck and still reach the bottom of the hopper.
Physical location of the probe is a basic but critical item. It should be positioned so that the truck doesn’t have to stop on an inclined ramp into the elevator. Also, there must be enough space between the probe and receiving pit to allow sampling the rearmost hopper of the truck while dumping the front hopper of the previous truck. As a guideline, the edge of the dump hopper should be at least 175 feet (53.3 meters) from the probe location.
The sample lines transferring the sample from the probe to the office can be either above or below ground. If lines are buried, flexible hose must be installed in a larger sleeve so that they can be replaced when worn out or removed if they become plugged. With buried lines, it is important to make the sleeves watertight where the sample lines exit from them.
Above-ground lines can be either flexible or rigid steel, or aluminum tubing. Be careful to use the appropriate inside diameter sample transport line as recommended by the manufacturer, since this must match the airflow capacity of the fans and blowers supplied. If using flexible plastic tubing above or below ground, be sure to use tubing with a smooth interior surface.
The other key installation concern is to ensure the sample receiver is airtight when not operating, particularly when the outside temperatures are cold. If the sample receiver is not airtight, warm, humid air from the grading room can enter the sample lines, cool off and condense, resulting in water in the sample.
It’s also important to balance the air flow to the probe. The air supplied to the
probe should just offset the air drawn out of it. With the air balance set properly, holding light chaff in your hand about one-half inch from the probe tip should result in the chaff neither blowing out of your hand nor sucking into the probe.
One complaint that has been leveled against truck probes is that they can damage the bottom of trucks, usually because of either operator error or probe design problems. Installing pressure relief systems in the downward pressure line to the probe can reduce the likelihood of significant truck damage by limiting the downward force to that which is required to push the probe through the grain. This may require contacting a hydraulic expert to oversee the installation. It is usually not possible to achieve this by just reducing the main system pressure, as other components typically require higher pressures. In some cases, it may be possible to simply replace the cylinder with a smaller diameter one or a larger rod to reduce the force available.
Another important issue is how to see where you are probing. The best way is to install the probe next to an elevated grading office where you can see the probe and truck directly. However, in many cases this is not possible and a video camera system is necessary. Unfortunately, video cameras present only a two-dimensional view, making it more difficult to judge location and depth.
If a video camera is needed, you should consider the following recommendations:
• Use a high-quality color video security camera. Expensive features such as remote zoom, pan and tilt aren’t always necessary. The most important thing is to place the camera in the right location and use good basic components.
• Install the power supply for the camera in a weather-proof box adjacent to the camera. The box is also handy to make the signal connections in a protected area. Do not install the power supply in the grading room, as it is difficult to avoid excessive voltage drop over the distance to the camera.
• Using a regular color television with a cheap coax to RCA video adapter will save hundreds of dollars compared to using a specialized video monitor.
• The camera should be positioned to look at the truck from an angle to give some perspective. Generally speaking, the camera should be about 18 to 20 feet high, parallel to the truck travel in line with the probe on the outbound side of the probe, roughly 15 to 20 feet from the probe mast. This is also a convenient location to mount an intercom for the trucker, if one is used.
• A light illuminating the probe area should be installed below the camera so it is not “blinded” by direct lighting.
• If possible, locate the probe controls where the operator can see it via an exterior window. This seems to help orient them with the video camera. The sample receiver should be located within reach of the probe controls.
Finally, a means of communication from the grading room to the trucker is necessary. A simple sign and traffic lights can be sufficient in terms of instructing the trucker when to move. However, some interactive communication is usually necessary to determine whose grain it is prior to reaching the receiving pit.
The best way of doing this is often a two-way radio, but that system can only work if the trucker has a compatible radio, which isn’t always the case.
The second choice is an intercom or telephone system. It is important to note that a relatively inexpensive intercom (in the U.S.$300 range) will not work acceptably because of wind and engine noise. The better choice is a weatherproof telephone handset type of system.
Several probe samples should be taken from each truck to improve the chance of it representing the entire load. At a minimum, two probes per compartment should be taken. In most cases, the deepest part of the truck should be probed.
Kevin B. Mason is senior project manager and division engineer for Agricore United, Winnipeg, Manitoba, Canada. He may be contacted at: firstname.lastname@example.org. This article is modified from his presentation at the 2007 GEAPS Exchange. For the full presentation, visit www.geaps.com.