--- title: "Gravimetric Feeder Accuracy in PLC Multi-Hopper Batching: A Buyer’s FAT Plan" date: 2026-10-17T01:54:00Z modified: 2026-10-28T02:12:37Z permalink: "https://www.hyflowtech.com/blog/basic/plc-multi-hopper-weighing-accuracy-fat/" type: post status: publish excerpt: "" wpid: 2605 categories: - basic featured_image: "https://www.hyflowtech.com/wp-content/uploads/2026/10/image2-8.webp" featured_image_alt: Three industrial hoppers dispensing white, yellow, and blue powders into a central weighing vessel. Technical overlay graphics illustrate a PLC control interface, load cell weighing, and system flow diagrams for evaluating gravimetric feeder accuracy and FAT plans. timestamp: 2026-10-28T02:12:37Z tags: - basic --- ## **Quick answer** Gravimetric [feeder](https://www.hyflowtech.com/wp-content/uploads/wp-mfa-exports/post/hopper-feeder-systems-guide.md) accuracy shows how closely each delivered powder dose matches its target weight. In PLC multi-hopper batching, individual ingredients as well as the finished batch should be checked, since a correct total can hide dosing errors. A factory acceptance test (FAT) checks performance through weighing verification and repeated trials against pass/fail limits agreed before ordering. ![Three industrial hoppers dispensing white, yellow, and blue powders into a central weighing vessel. Technical overlay graphics illustrate a PLC control interface, load cell weighing, and system flow diagrams for evaluating gravimetric feeder accuracy and FAT plans.](https://www.hyflowtech.com/wp-content/uploads/2026/10/image2-8-1200x675.webp) ## **What Accuracy Means for Each Ingredient and the Full Batch** The weight of a batch can be exactly what’s required by the recipe and still have the wrong ingredient proportions. Let’s say a recipe calls for 20 kg of sugar and 80 kg of flour. If the equipment delivers 19 kg of sugar and 81 kg of flour, both ingredients miss their targets, even though the total still comes out to 100 kg. Each delivered weight is compared with its target to measure ingredient accuracy. Meanwhile, batch accuracy compares the combined weight with the recipe total. Both measurements matter, especially when small differences in ingredient quantities can affect product quality. The dosing method used also affects accuracy. Powder is measured by weight when using a gravimetric feeder, whereas volumetric powder dosing uses a [screw](https://www.hyflowtech.com/product/sanitary-screw-conveyor-hopper/) or another mechanism to deliver a set volume. As powder density can vary, the same volume may contain different amounts of powder by weight. ## **PLC Parameters: Slow-Start, Pre-Act and Feed Speed** How much powder reaches the scale before feeding stops is influenced by PLC settings. During FAT, it’s important that buyers verify how each stage is handled by the proposed controller. - **Slow-start:** The feeder starts gently or increases speed gradually. With this, it may be possible to control an initial surge of powder, depending on its flow behavior. - **Feed speed:** Most of the target dose is delivered in the fast stage. The amount entering the vessel as the target approaches is reduced by a slower final stage, allowing finer control over the final dose. - **Pre-act:** Some powder may still be falling when the feeder stops. Pre-act allows the controller to stop early to account for the remaining material. For instance, if 10 kg is the target and tests show that another 0.1 kg arrives after cutoff, a 9.9 kg stopping point may produce the intended final weight. These values need to be tested using the intended powder. Ask the supplier which settings can be adjusted and whether compensation is manual or automatic. The presence of a PLC alone should not be taken as proof that either feature is available. ![Industrial stainless steel multi-hopper powder dosing system featuring several conical hoppers with blue motor drives, connected by feed tubes to a circular rotary platform holding multiple lidded ingredient containers for automated batching and mixing.](https://www.hyflowtech.com/wp-content/uploads/2026/10/powder-900x1200.webp) ## **Calibrate Each Station and the Main Weighing Unit** FAT should start by verifying the scales before evaluating feeder performance. If a central receiving scale and separate ingredient weighing stations are present in the proposed system, you’ll want to check each one. With the vessel empty, confirm the zero reading before anything else. Then, verify the displayed reading across the working range by applying suitable reference weights. These checks should be repeated for the main weighing unit and each weighing station, with the results and any adjustments recorded. It’s also important to check for any physical interference, as forces can be transmitted to a load cell by a rigid connection. Likewise, readings can be made unstable by nearby vibration, with residual powder also affecting tare readings. When it comes to scale capacity, small ingredient additions may not be resolved well enough for their specified tolerances by a scale sized for a large batch. As such, you should ask the supplier to demonstrate not only the largest required dose but also the smallest. Keep in mind that calibration verifies the weighing system. Because the feeder can still deliver inconsistent amounts or overshoot, calibration alone doesn’t establish [powder dosing](https://www.hyflowtech.com/wp-content/uploads/wp-mfa-exports/post/how-to-prevent-powder-bridging-in-hopper.md) accuracy under running conditions. ## **Build a Repeated-Run FAT Matrix** A useful FAT matrix is one that tests realistic doses across the intended operating range. Small additions as well as large and medium quantities must be included, after which each test must be repeated under agreed conditions. The following results are illustrative, using an assumed ±1% tolerance. They are not published performance figures for HYFLOWTECH equipment. | **Dose** | **Run** | **Target** | **Actual** | **Deviation** | **Result** | | --- | --- | --- | --- | --- | --- | | Small | 1 | 2.00 kg | 2.03 kg | 0.015 | Fail | | Small | $2 | 2.00 kg | 1.99 kg | −0.50% | Pass | | Medium | $1 | 20.00 kg | 20.08 kg | 0.004 | Pass | | Medium | $2 | 20.00 kg | 19.94 kg | −0.30% | Pass | | Large | $1 | 50.00 kg | 50.20 kg | 0.004 | Pass | | Large | 2 | 50.00 kg | 49.85 kg | −0.30% | Pass | **Percentage deviation = (actual weight − target weight) ÷ target weight × 100.** As you can see, the first small-dose run fails despite the error being only 30 grams. This matters when a recipe doesn’t allow much variation in a minor ingredient. The powder and the PLC settings used for each run must be recorded. It’s also crucial to agree on the number of repetitions beforehand; the two runs shown here only demonstrate the table format. Ask the supplier to run enough trials at each dose size to show whether results remain consistent, rather than merely whether one or two runs pass. Note that the behavior of the production material can be different if the factory uses substitute powder. A successful test should reflect the conditions buyers expect in production, rather than an idealized demonstration. ## **Review Error Displays, Alarms and Exported Data** FAT should not only show operators what happens during a successful batch. Instead, it should help them see what happens when a dose goes wrong so they know how to respond. You can ask the supplier to simulate an underfeed or overfeed condition and demonstrate the response. The affected ingredient and problem should be clearly visible on the display. Plus, check how a weighing signal fault and an interrupted batch are handled by the proposed system. Agree on the next steps before proceeding. For instance, should a controlled recovery sequence be implemented, or will the process stop until an operator reviews the error? If batch records are needed by your quality team, make sure to specify the required information before ordering. Some useful fields are the batch identifier and actual ingredient weights alongside their targets. Seek confirmation that the proposed configuration can export those records in a format your team prefers. PLC control alone doesn’t guarantee these reporting or alarm functions. [ ![Sanitary Semi-Automatic Powder Hopper](https://hyflowtech.b-cdn.net/wp-content/uploads/2026/04/2Semi-Automatic-Powder-Hopper.jpg) **Sanitary Semi-Automatic Powder Hopper** The Semi-Automatic Powder Hopper is a specialized stainless steel vessel designed for controlled dosing and discharge of powder and granular materials in sanitary processing environments. View Details ](https://hyflowtech.com/product/sanitary-semi-automatic-powder-hopper/) ## **Agree Pass/Fail Criteria Before Ordering** The acceptance rules can be put in the purchase specification before the equipment is built. It’s better to state the allowable deviation for each ingredient rather than specifying just a single tolerance for the overall batch. Define the number of runs that will be tested and what happens after a failure. Plus, specify the dose sizes and powders to be used during FAT. It’s also a good idea to document the weighing checks and any reporting or alarm demonstrations. HYFLOWTECH’s [sanitary semi-automatic powder hopper](https://www.hyflowtech.com/product/sanitary-semi-automatic-powder-hopper/) is offered in standard 30 L, 50 L and 60 L sizes, with custom volumes available. Its published specifications describe screw-feeding options and PLC touchscreen control, but don’t establish a complete multi-hopper gravimetric weighing configuration or a guaranteed FAT tolerance. For a custom system, buyers should confirm the weighing layout, PLC settings, and FAT acceptance criteria with HYFLOWTECH before ordering. A written FAT plan then gives both parties a clear way to judge whether the delivered equipment meets the agreed requirements. [ Contact US ](https://www.hyflowtech.com/wp-content/uploads/wp-mfa-exports/page/contact-us.md)