July 10, 2026

The Complete Guide to Improving Precision and Accuracy in Industrial Batching Processes Precision and accuracy are not the same. If you produce a batch of, say, 1,000 ketchup bottles that are underweight, you need to know whether your filler is incorrectly set (accuracy) or if your filler is repeatable but consistently producing a low weight (precision). Because you can’t manage what you can’t measure, you need to understand the type of error in your filling line. Any system you use needs to be specified and calibrated correctly. The number of samples for calibration can’t be chosen arbitrarily, and calibration must be carried out with a calibrated system. Your scales and the weight control system must allow for the accuracy and precision you need as well. Volumetric vs. gravimetric feeding: choosing the right method The first choice a processor has to make with any batching system is whether to feed by volume or by weight. Volumetric feeders move material at a constant speed and assume the bulk density of the material is also constant. This assumption is violated by pretty much all bulk solids you’ll ever work with in the real world. Moisture content varies from lot to lot. Particle size distributions shift from vendor to vendor. Powders can compact in the feeder based on how long they’ve been in storage. Any of those factors changes the mass-per-volume ratio, meaning the contents of the feeder hopper are not what the processor believes they are. Gravimetric feeding (called loss-in-weight feeding with continuous processes) simply sidesteps this problem. The feeder sits on a load cell, and as material discharges the controller monitors the rate of weight loss. It then speeds up or slows down the feeder as needed to maintain the desired mass flow rate. If the material has aerated and the bulk density has temporarily gone down, the feeder runs faster to keep feeding the right number of pounds per hour. If the material has compacted or started clumping and the bulk density has gone up, the feeder runs more slowly. Volume rises and the feeder speeds up, volume falls and it slows down, and the problem of unknown bulk density takes care of itself. Gain-in-weight (GIW) batching is based on the same principle of weigh as you go, but instead of weighing the feeder, the system weighs the collection vessel. Raw materials from several feeders discharge one after another into a single central hopper that is mounted on load cells. The accumulating material is weighed, which tells the controller when enough of a given ingredient has been dosed and it’s time to move on to the next one. GIW is good for recipes with many separate ingredients where the order they’re added in must be carefully controlled. It’s also easy to audit – you can see the screen and the scale head and tell pretty easily what was added, why, in what amount. The physics of in-flight material compensation When a feeder turns off to conclude a dosing phase, some material is still in motion. There is a section of product extending from the discharge point to the scale hopper – still airborne, not yet detected by the load cell. This is in-flight material, and if the PLC doesn’t consider it, every batch will be low, then over the target once that material lands. A good control system uses a pre-act value to factor in that there is material still en route: an estimated cutoff point which instructs the feeder to turn off before the scale reaches the targeted weight and allows the in-flight material to arrive and finalize the batch. The number isn’t static. Material density fluctuates. Feeder rate speeds up and slows down depending on how full the hopper is. And temperature and humidity alter how easily the material flows from the discharge point. A modern system will dynamically learn the pre-act value: Adjust the expected cutoff based on how the last few batches actually performed. If the in-flight weight was greater than planned and the batch was over, the next cycle or two will add material more slowly. If it was under, the next cycle or two will add material more quickly. That’s a closed-loop correction – and one of the most obvious ways to show that it isn’t the hardware, it’s the quality of the programming in the PLC that matters. Load cell interference and vibration mitigation Load cells are the foundation of any gravimetric batching system, and they’re among the easiest parts to damage in a plant setting. Essentially, they read weight by monitoring the microscopically small mechanical strain of a metal component – often less than a quarter of a degree of arc. Any external shock or vibration in the area can throw those measurements out the window. Mitigating the issue happens both physically and digitally. At the component level, scale assemblies should be mounted on anti-vibration pads to decouple them from the floor structure. Piping connections can pass vibrations; flexible couplings that allow the scale to move freely without restricting movement in the roll and pitch axes are recommended. From the controls side, PLC or PAC programs can apply filter functions to remove high-frequency noise components from the load cell signals. These low-pass filters won’t affect the signal from the real, slow weight changes due to material backup in the system. Filter settings are specific to each installation, and too-strong a filter will reject legitimate data right along with the noise and give the impression of sluggishness. Material flow behaviour and the role of feeding hardware Powders and dry bulk materials often do not behave as expected. Small particles aerate, causing the powder to act like a liquid and rush through gates. Particles with irregular shapes or high moisture content or that have a natural affinity for each other clump together and block the flow. These erratic conditions can have a number of root causes but two fundamental solutions: introduce a device to help the material feed reliably, or slow down the entire filling process to ensure that the product filters through at a rate that can be controlled. Of the two, using a flow aid or mechanical agitator to keep the hopper outlet active will produce more consistent and more accurate batches so long as it’s selected and applied appropriately. Equipment like pneumatic feeders use controlled air pressure and fluidization to move difficult bulk solids – fine powders, hygroscopic materials, and sticky products – from storage into the batch hopper without causing segregation or compaction at the discharge point. Of course, if the material flows naturally, there is no reason to install a costly-and-maintenance-prone piece of equipment. Also, remember that if the feeder itself is the problem (and the material is flowing without trouble in the silo or hopper), a flow aid, aeration pad, air sweep, or mechanical vibrating agitator will not solve the real problem. Calibration procedures and scale verification Calibration can’t happen once with the assumption that things are good for the life of the scale. It happens constantly, as the scale is exposed to forces and conditions that slowly influence its accuracy over time. Temperature fluctuations happen all the time, even if your scale is in a climate-controlled area. As the temperature changes, scale components expand and contract, and this can cause the scale to slowly drift into being out of calibration. HVAC currents may seem trivial, but even a small breeze across the surface of a scale can cause a reading. Multiply that by the number of open dock doors or forced airflow, and the many fine balances will be impacted. As your scale ages, the surfaces where check rods rest can become slightly worn, changing the precise balance point of the scale. The same can happen with the metallic bearing points that a load cell is mounted through. Over time that area could change, causing the load cell to read differently despite the same weight being measured. The standard way to verify your scale is by using certified test weights. These are physical masses that have a documented calibration certificate that traces them back to the redefinition of the kilogram. You apply them to the scale assembly and see if the system’s displayed reading matches the reading you would expect from the weights attached. The frequency that you should do this varies based on your usage. Do you move a lot of products on and off that scale in a given timeframe with very tight tolerance for error? Then you should be checking the scale more often than if you move a few items on and off a scale over the course of a month, and the error can be a bit larger. A well-kept calibration log will record the date of the calibration, the weights used, the found error, and if there was a corrective action. This gives you both an audit trail as well as an early warning system that you’re developing an out-of-tolerance situation. If every found error seems to be in the same direction, you are developing a systematic trend – and those aren’t random. Something is actively changing mechanically, and you’re about to exceed tolerance. Transitioning from manual to automated batching When the system encounters an error, the operator doesn’t have time to troubleshoot the automation. Instead, the computer has to immediately produce a list of everything outside its tolerances or that could have gone wrong. The operator has to identify at a glance the missing pieces of information or correction methods, or be able to deduce which sensor has drifted and by how much if the computer displays inconsistent percentages. For that kind of immediate, complex pattern recognition with so little margin for error, the computer can’t replace a human. Workforce training for automated material handling According to PMMI, human error and improper equipment setup can be up to 60% of unscheduled downtime and batch quality deviations in automated processing plants. Although implying automation is the solution is tempting, it’s the training that needs the upgrade since many of these plants are already automated. The technology investment has been made. It’s the human side that needs work. When considering training for automated material handling, you can’t be happy with just training a person to know what button to push. That’s a good start, but to achieve true operational excellence, training must go further, often including these three areas. First, HMI interpretation. It’s good to know that when an error code pops up and displays E-14 it’s time to call maintenance, but it’s much better to know that E-14 indicates the loss-in-weight system lost track of its refill cycle, and that can be caused by a valve that did not operate correctly. Here’s how you can determine if it’s a sensor malfunction or a mechanical failure. Secondly, consider material lot management. Raw material characteristics differ from lot to lot of the supplying source. An experienced operator knows to sample bulk density of the new lot and compare it to the previously sampled and tested lot. Then, they know how to avert the consequences of a difference by making the necessary changes to the feeder’s weight control parameters before the new material begins to cause over or underweight product, rather than after. Thirdly, consider component preventative maintenance. Load cell mounting hardware, flexible connections, vibratory tray, screw flight surface all degrade over time. The experienced operator knows to look for wear and how to adjust for the wear during routine inspections. A worn screw flight feeding 4% less material per revolution doesn’t alert anyone or fail – it just quietly multiplies the underweight product over thousands of cycles until a quality check exposes the variance. This investment in training pays back directly through lower batch rework, lower raw material waste, and lower unscheduled maintenance. Hardware doesn’t output product, people operating and maintaining the hardware control how closely they come to the designed output. Keeping the system honest over time Ensuring precision batching is an ongoing effort rather than a one-time task. This involves performing regular calibration checks, maintaining proper documentation, and having operators with enough knowledge of the equipment to recognize early deviations. Aeration, bridging, bulk density shift, in-flight compensation, and other physical science factors of bulk solids handling lead to problems that are not easily solved by generic responses. They need to be understood, and understanding needs to be at the plant floor level, not just within the engineering team’s manual. So, to sum up, you need the right hardware, proper calibration, and well-trained operators. That’s what it takes to achieve precision batching.