Grain and Feed Silos: Inventory, Alarms and Batch Control

Technical guide by Arvin, METRAVON Instruments · Reviewed September 2026

Short answer

Separate a grain or feed project into four functions: continuous level for inventory trend, independent point-level alarms for overflow or starvation protection, blockage detection for material flow, and weighing for mass or recipe control. One level value should not be expected to provide accurate stock settlement, a critical high-high trip and batch traceability at the same time.

Dust, sloped surfaces, bridging, rat-holing, changing moisture and multiple grain varieties can all change the relationship between measured level and actual mass. Define the business result and acceptance method before selecting instruments.

Match the measurement to the decision

Continuous silo level

Non-contact radar is often evaluated first for grain and feed silos because it avoids direct contact with the material. Confirm silo height and diameter, filling point, roof structure, internal braces, expected material peak, dust, process temperature, nozzle geometry and hazardous-area requirements.

Mount the radar away from the filling stream and check the complete beam path. Record echo behavior during actual filling, when dust and surface movement are greatest. An empty-silo test cannot demonstrate tracking under the most difficult condition.

Inventory conversion

Level-to-volume conversion requires a vessel strapping table that includes the roof and hopper geometry. Volume-to-mass conversion requires a representative bulk density. Keep separate parameters for different grains, feed formulations or moisture ranges rather than applying one fixed density to every product.

Retain the original distance or level value alongside calculated volume and mass. When stock differences are investigated, compare the strapping table, density, wall buildup and surface model separately. For direct mass measurement, evaluate silo weighing and its structural load path.

High, low and blockage alarms

Calculate a high-high trip from maximum inflow, conveyor transport time, stopping delay and remaining safe capacity. Install the point switch outside direct material impact. A critical trip may justify an independent technology and signal path from the continuous level instrument.

At the outlet, distinguish low inventory from no flow. Bridging or rat-holing can stop discharge while material remains in the silo. Combine level information with feeder status, motor load or a suitable flow/blockage signal where the process consequence requires it.

Batch weighing and recipes

Define minimum and maximum ingredient targets, allowable error and cycle time. Minor ingredients may require a dedicated smaller scale because their target is too close to the division and noise of a main-material scale. Use coarse and fine feed, controlled cut-off and in-flight compensation, then verify consecutive batches rather than one successful cycle.

Batch records should contain product and recipe version, batch number, ingredient targets and actuals, deviation, timestamps, alarms and manual corrections. Link raw-material lots to production batches when traceability is required.

Dust, hygiene and safety

• Confirm dust hazardous-area classification and electrical protection from the project safety design.
• Use bonding, grounding and static-control practices required by the plant.
• Review product-contact materials, cleanability and contamination risks for feed or food applications.
• Provide safe access for inspection without relying on routine silo entry.
• Do not treat a website product category as evidence of suitability for a specific dust zone.

Commissioning and acceptance

1. Verify silo identity, product, dimensions, mounting, range, outputs and alarm cause-and-effect.
2. Check level at empty or known reference, normal operating and near-high conditions.
3. Observe filling and discharge trends for false echoes, jumps and implausible rates.
4. Trigger high-high, low-low, blockage and device-fault conditions through the complete control loop.
5. Run repeated minimum, normal and maximum recipe batches and calculate error and cycle-time statistics.
6. Reconcile silo number, material variety, batch and inventory records across the local and remote systems.

Information required for selection

Provide material varieties, particle size, moisture and bulk-density ranges; silo dimensions, roof and cone drawings; filling and discharge arrangements; dust and temperature; alarm functions; recipe targets and tolerances; cleaning and hazardous-area requirements; power, output, communication and inventory-platform requirements.

Frequently asked questions

Why does silo tonnage differ from a weighbridge total?

Level-based tonnage depends on the vessel-volume table, surface shape, wall buildup and bulk density. Audit those conversion inputs before assuming the radar distance is wrong.

Can continuous radar provide the only high-high alarm?

It may provide an operating alarm, but critical overflow protection should be assessed for independence and common-cause failure based on the process risk.

How can feed batching errors be reduced?

Match the feeder to material flow, use coarse and fine dosing, compensate material in flight and verify repeated batches at the smallest and largest targets.

Is a remote inventory platform always necessary?

It is valuable for multiple silos, plants or purchasing coordination. First ensure the field measurement, identifiers, alarm logic and offline behavior are reliable.

Separate inventory, protection and recipe functions

A grain or feed silo normally serves several users. Purchasing wants stock, operations wants available runtime, maintenance wants instrument health, and production wants reliable dosing. Do not force one signal to satisfy every purpose. Continuous radar supports level trend and estimated inventory; an independent high-high switch protects against overfill; load cells or a batch scale measure mass; feeder and flow diagnostics identify a blocked outlet. Define the owner and required response for each function.

For overfill protection, calculate residual inflow from conveyors, elevators and pneumatic lines after the stop command. For low-level control, account for the outlet cone and possible rat-holing. The sensor mounted at the wall may remain covered while the centre has emptied. Confirm the chosen point during real filling and discharge rather than only with an empty vessel.

Material behaviour changes the measurement

Record grain type, particle size, moisture, fines, temperature and bulk-density range. Aeration, fumigation, transport and storage time can change packing. A radar distance can remain accurate while the mass estimate shifts because density and surface shape have changed. Preserve the raw level and identify which density is applied to each calculation.

Dust during pneumatic filling can weaken echoes and coat antennas. Bridging, wall buildup and asymmetric filling make a single point less representative. Select a mounting point away from the inlet stream and internal bracing, then examine the echo curve during the most severe filling condition. Wide silos or multiple inlets may justify more than one point or a stated wider inventory uncertainty.

Batching and micro-ingredient control

Translate formulation tolerances into absolute mass limits for every batch size. Separate major ingredients from micro-ingredients when one weighing range cannot provide the required resolution. Use coarse and fine feed, stable cut-off compensation and confirmation that material actually flowed. A running screw or open gate does not prove delivery when product bridges.

Link every actual addition to recipe version, raw-material lot, scale status and batch identifier. Record manual corrections and substitutions. If an ingredient is outside tolerance, the system should apply a predefined disposition rather than allowing an operator to erase or overwrite the original value. This is essential for feed safety, customer complaints and yield analysis.

Hygiene, contamination and combustible dust

Review cleanability, pest control, allergen or medicated-feed segregation and retained material. Avoid pockets around probes and process connections. Confirm whether the dust atmosphere requires hazardous-area equipment, bonding, grounding, explosion venting or isolation. Instrument certification does not replace the plant dust-hazard assessment.

Maintenance work must control ignition sources and prevent entry into confined spaces without an approved procedure. Air purging or cleaning devices need compatible pressure and air quality. After cleaning, inspect seals and verify that the sensing element has not been bent, blocked or moved.

Acceptance and performance monitoring

Commission radar at empty, intermediate and high conditions and observe dynamic filling. Prove high-high and low-low functions through the final conveyor, gate or alarm. Run representative recipes that cover large and small additions. Reconcile inventory over several receipts and consumption cycles instead of adjusting the system after one comparison.

Trend signal quality, alarm frequency, feeder time, batch deviation and zero stability. Rising feed time may indicate flow deterioration; repeated high-level alarms may indicate poor timing rather than a failed switch. Use these indicators to target maintenance and review setpoints after product or handling changes.

Information to include in an enquiry

Supply silo drawings, grain or feed type, density and moisture range, filling and discharge equipment, maximum rates, dust classification, required alarms, batch sizes, tolerance, interfaces and site photographs. Identify whether the requested result is level, estimated tonnes, direct mass or protective shutdown. State cleaning, allergen and traceability requirements so the proposal covers the complete duty rather than only a sensor.

Engineering note: Grain-dust explosion protection, hygienic design and legal metrology requirements must be confirmed for the actual plant, jurisdiction and intended use.