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
In Motion Checkweighers are an important part of many industries
Just think about it: how many of the items you buy in the grocery store have weights marked on them? Just about every food item, many pharmaceutical items, personal hygiene items, the list could go on and on.
Now think about how those products can be weighed. The most common way most people would think of is static weighing. In order to weigh statically, whatever is being weighed is physically placed on the scale and physically removed. A good example of static weighing would be your normal bathroom scale or the scale the meat counter at the grocery store uses to measure out the meat from the meat case.
Static weighing works well, but what if you had to weigh thousands of products each day? There would have to be a more efficient way to do that, wouldn’t there? There is a more efficient way and that is in-motion weighing! In-motion weighing weighs those products while they are moving so they don’t have to be manually placed on a scale and manually removed from the scale.
Weighing products while they are in motion can greatly increase the amount of product that flows through the plant each day.
No more repetitive manual labor is needed to weigh it and in-motion weighing can be very accurate when done properly.
In addition to just taking weights, an in-motion scale can perform many other important functions including weight reporting, checkweighing, and sorting. But that is a topic for another time.
Next time you’re looking to weigh your product and need to move a lot of product while still weighing it, consider an in-motion weighing system. You won’t regret it!
An in motion checkweigher’s main purpose is to weigh and reject out-of-spec products, but that doesn’t mean that it can’t serve other purposes as well. It can also work well as part of a larger system by feeding back important information to machines up the line, allowing them to do their job better.
A good example of this would be in a plant producing chubs of ground meat product.
When chubs are packaged, they are filled by a pressurized machine which is set to a certain amount of pressure and filling time in order to get the right amount of ground meat. From there, you can pass all of these chubs over a in motion checkweigher to ensure that they meet a minimum fill level.
The rate of the machine output is often roughly two per second, so we make sure that our in motion checkweigher can match that. As the chubs pass over the in motion checkweigher, the scale verifies that they are at an acceptable weight and then rejects them if they are not, but it can also gather information that could benefit the filling machine.
With special diagnostic software that we offer, this process can be optimized for minimum product waste and giveaway. When linked with the checkweigher data, this software can take a sample of a number of chubs crossing the checkweigher and take notice of the filling trends.
For example, the software allows you to specify levels that you have to meet (i.e. one pound of ground meat product) and acceptable levels of overfilling.
The checkweigher can report weights to the software which determines how many packages were overfilled or underfilled. Given this information, the in motion checkweigher can then send a signal (voltage) to the filling machine to adjust its filling parameters. If the in motion checkweigher is rejecting too many products for being underweight, it can tell the filling machine to increase the pressure or fill time to bring the packages to an acceptable level.
In addition, the software can provide daily reports to help the company know their profits and whether they need to perform any maintenance to bring the filling machine up to speed.
An in motion checkweigher is a necessity for its main functions, but its secondary functions shouldn’t be ignored either! There is a lot of money spent on product giveaway and reworking to be saved by using a combination like this.
If you have questions and want to hear more about our in motion checkweighers, contact us today!
In-Motion Checkweighers all perform the same function of checking products to see that they fall into an acceptable weight range, but not all in motion checkweighers are exactly alike or follow the same principles. In the industry, there are actually two typical ways of making a in motion checkweigher that function off of different concepts of weighing and loading. The first one, which we use for all our checkweighing systems, is the concept of mounting a powered conveyor on a load cell based scale device, motor gear box and all.
This is a challenging proposition because the powered conveyor must be light enough to allow proper scale sensitivity, yet large enough to convey the heaviest product the checkweigher will see. The other method that gets used by some companies is to drag a conveyor belt across a weigh bed. This method allows use of heavy duty motors but generally yields poor repeatability results and requires engineering equations which can relate deflection back to weight.
So while they still reject products in a similar fashion, the method we use will give more repeatable results.
Both methods have their ups and downs, but they accomplish the same purpose.
Using the actual scale conveyor mounted onto the load cell helps us to achieve a great level of accuracy and repeatability, which is advantageous when seeking NTEP Approval.
There are not many people who produce NTEP approved in motion checkweighers, but we choose to go that extra step.
In-Motion Checkweighers are not required to be NTEP approved, but it is a great benefit to have.
There are many companies making in motion checkweighers these days, showing that they are becoming more and more of a necessity for certain plants, but we go the extra mile to ensure our product quality and accuracy.
Don’t buy just any old In-motion Checkweigher.
Get in touch with us for the best possible checkweighing experience!
Anyone who works on in motion checkweigher and digital weighing equipment (such as a bench scale, laboratory balance, etc.) knows the relatively simple task of weight testing the scale with known test weights.
It is simple right? You turn off automatic zero tracking (AZT), verify that the scale is at center of zero, then apply known test weights and compare the displayed value against the actual weight applied. You check it at several different weight values and provided you have a good static scale, bingo you are done! Simple right?
Now, put the test weight in-motion across the scale and suddenly things get really confusing. You run the weight once and you are done right? WRONG!!!! This is where statistics rears it’s ugly head. Often when you run the weight across the in-motion checkweigher, it weighs different! What should you do!?
Steps To Success
- Same as the static scale, check zero both static and in-motion.
- Get a product (one single example) that represents the product that you intend to check weigh in-motion or dynamically. Then verify the exact weight of that product on a very accurate static scale. You now have what is known in the industry as a “test puck.”
- Turn the in-motion checkweigher on (run the belt) at the speed that you intend to use the in-motion checkweigher in production.
- Apply your test puck to the infeed belt well ahead of the weighing section of the in-motion checkweigher to allow relative motion of the test puck-to-belt motion to stabilize before the test puck arrives on the in-motion checkweigher’s live section. Then collect the test puck after the in-motion checkweigher’s live section once weighing is complete.
- Record the in-motion checkweighers in-motion value.
- Repeat steps 4 and 5 at least 32-100 times. (no I am not kidding!)
- Verify that zero did not change or you will need to start over.
- Verify that the test puck static weight is still the weight value when you started or you will need to start over.
- Analyze the results by determining the highest and lowest values, the difference is the spread, then average all the in-motion values and compare against the actual static weight of the test puck, oh yes don’t forget standard deviation calculations!
- Ask yourself, ARE YOU SATISFIED? If so, congratulations!! You are done (for now) as soon as you file the results to compare against future testing results.
Following the above steps, as tedious as they seem, will give you a clear picture of the true accuracy and repeatability of your in-motion checkweigher. Future testing with similar results will prove the performance is staying constant while variations with trends can indicate problems with the checkweigher.
Obviously, if any kind of change is made, it is time to test again. Be very careful to never change more than one thing at a time, as it becomes impossible to tell performance changes based on the “thing.”