Time and strain can become evident when a difference is apparent in trolley movement from one side to the other of a multi
This should be verified by using certified test weights to check the scale operation on a frequent and recurrent basis. If the weight is not correct from one end to the other, adjustment may be possible at the summing card if weighment error appears consistent. Just as with people, not all parts wear down the same way. This type of problem could be attributed to simple metal fatigue or electrical properties internally.
The good sign, however, is that the apparent problem appears consistent, thus it is possible for it to be corrected by simple adjustment and calibration. When the weight indication is not consistent and is grossly incorrect on one side as opposed to the other side, a load cell or summing board is most likely at fault. Load cells have an internal strain gauge, and as alluded above, the strain over time can sometimes be fatal, and load cell replacement is required.
Maintenance people sometimes check for this situation by testing load cells for correct resistance values. Consistent and large error weight indications across a load cell are often a good indication it’s time for a change. When problems are specific and consistent, they can sometimes be easy to identify and subsequently rectify.
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Once a product is weighed on the conveyor, a reject device of some sort will be needed to remove the out-of-weight (or out-of-tolerance) items from the line. Most of these devices will need a power source of some sort to activate the reject device. The most common power sources that come to mind are pneumatic, electrical, and hydraulic. For this article, the focus is pneumatically operated devices.
Many types of pneumatically operated devices can be manufactured and installed on an in-motion checkweigher.
Here are five types of pneumatic reject devices:
The first option is a simple air knife or air comb device. These devices simply blow a puff of air at the product and blow it off the line. These are typically used on very light-weight products since they do not physically push or pull the product.
A second option is a linear thruster.
A linear thruster mounts to the side of the conveyor and pushes the product straight off the other side of the conveyor.
A third option is either a pull-off or push-off arm. An arm of this type has an arm tied to the pneumatic cylinder with a pivot point on the side of the conveyor. When activated, the cylinder pushes the arm open while the arm pivots about the pivot point. It either pushes product off the opposite side of the belt or pulls it off to the same side the divert is mounted on. As it pushes, it also guides the product to the desired side.
A fourth reject device is an overhead mounted guided cylinder. A cylinder is mounted between guided rods with a block mounted on the guided rods. The cylinder moves the block along the guided rods. A plate of some sort is mounted to the block and hangs down along the side of the conveyor. This plate moves with the block to push product off the side of the conveyor.
A fifth type of reject is called a drop-down reject. With this type of divert, the conveyor itself actually has a pivot point located at the beginning of the conveyor and drops down to direct product off the end of the lowered conveyor.
Each of these types of pneumatic reject devices work well when used for the proper applications. If you have any questions about in-motion checkweighers, in-motion sortation, grading, classifiers, etc or whatever reject device would work well for your application, please contact us!
Although conveyor scales and checkweighers appear to be very similar, they are two entirely different entities. The ultimate difference between them is that one is a system and one is a component to be part of a system.
The in-motion checkweigher is defined as a system because it is formed of several components that form a single working unit. It is composed of an infeed conveyor, a conveyor scale, and an outfeed conveyor with some sort of diverting device, all as one unit.
The sole purpose of a checkweigher is to take a weight and check that against a user-specified range. If a product is inside this range, it passes through, down the conveyor. If not, the divert rejects the product onto another conveyor or container to be disposed of or reworked. This is all decided by software that is unique to the checkweigher.
Notice that a conveyor scale was just a single component of the checkweigher itself. A conveyor scale simply generates the weight of the product as it passes over. This makes it versatile.
A conveyor scale can be connected to a sortation system or an automatic labeler quite easily so that these systems can receive accurate weight information. Simply put a conveyor scale is just that – a scale that weighs products as it is conveyed over the scale’s live area, without stopping.
A checkweigher is more akin to a combo of conveyor scale and sortation system, except the sortation system only has two options: pass or fail.
As an example of how they differ in practice, let’s look at a producer that uses fixed weights and another that labels by weight (catch weight). For the former, a checkweigher is going to be far handier than just a conveyor scale because it can be programmed to reject any product that is below the minimum weight. Likewise, a conveyor scale is more valuable in the latter because it can link to a weigh price labeler and is capable of relaying individual weights to any number of systems.
The difference isn’t always obvious, but it is important to know the industry lingo when it comes to automatic systems.
It can save you a lot of trouble in the long run!
See our Checkweigher Conveyor Scales
Our multi cell static monorail scale is available in capacities up to 4,000 lbs. The length of the live rail can be as short as 12” and as long as 48.” Even though it is not a motorized in-motion scale, there are still some preventive maintenance steps you should perform for the sake of weighing accuracy as well as safety of plant personnel who work in the vicinity of the scale.
Inspect the live rail clearance. On a regular basis, you will want to look at both ends of the live rail and search for any debris that might have accumulated in the gaps because the live rail must be able to move freely and without any encumbrances. Another item to look for is any flaring of the live rail. If the live rail and the dead rail are touching, the scale’s weighing accuracy will be compromised.
Check for fastener corrosion. With the relatively high capacities of these scales, fastener corrosion could lead to a safety issue. By regularly inspecting the fasteners and replacing corroded ones as needed, you will be going a long way toward assuring yourself that valuable and dangerously heavy loads will not suddenly crash to the floor. Use only 140,000 PSI or higher-rated fasteners on rail attachment points.
Calibrate with test weights. Testing your multi cell static monorail scale with test weights should be a regular occurrence. Since, as its name makes clear, there are two load cells, setting the calibration may require adjusting the summing card, the weight indicator, or both.
Torque and seal. When it is necessary to change load cells, be sure to follow all the steps in the manual. Insist that only high strength L9 bolts and flat washers are used to attach load cells to the scale frame. Final torque values need to be carefully adhered to. Also, where directed to, be sure to use appropriate thread locking compound.
We can help you get a static monorail scale that fits your needs now and also help you get years of safe, dependable performance.
That is why we make our in-motion shackle scale. It is a non-legal-for-trade, steel monorail scale that is built to be very strong, and it allows you to get weighments for each carcass that comes in to the plant. This offers far more accurate yield calculations, which is important information for management. Still, there are a few issues to avoid.
There is an ideal place to install your shackle scale on your line, but often it gets put into a poor location. The scale should optimally be placed shortly after some sort of trolley indexing system and the outbound area should tend to move carcasses away from the scale. Having a poor installation location could mean that carcasses don’t flow correctly over the scale. If carcasses get too close together, the scale could have multiple animals on it at once.
To protect the scale against this, we created it with extreme durability in mind. It has a 5000 lb capacity, which is more than enough for the biggest animals. This ensures that it won’t experience any mechanical failure from multiple carcasses stacking up on the scale.
Another thing to be concerned about is maintenance accessibility. Often, the incoming monorail is rather high up in the air, and this is normally where you would install the in-motion shackle scale. A scale at this height could be difficult to get to for cleaning and service.
Many plants solve this by installing some sort of platform which is accessed via a ladder or steps. This provides a manageable and safe work area for any maintenance technicians.
Lastly, it might be difficult to avoid, but sometimes animals might have involuntary reactionary movements which cause them to jolt while on the shackle. This can cause errors and fluctuations in your readings. About the only thing you can do in this situation is use a weight indicator filter to decrease the noise in your data.
Our shackle scale can take a beating and still you give you reliable data
, so if you are looking for something that can handle weighing whole animals before going through the protein harvesting process, it is your best in-motion option.