Practical Procedure · Calibration

Load Cell Calibration for Weigh Feeders — Dead-Load, Test-Weight, and Why Shunt Calibration Isn't Enough

Applies to: Belt weigh feeders, weigh hoppers with load cell-based measurement | Equipment needed: Certified test weights or a dead-load/material reference, shunt calibration resistor (if supported), digital indicator/weigh controller access

Before You Start

Confirm the feeder/hopper is mechanically free — check idlers, belt tension, and load cell mounting for anything that could add friction or false load before assuming a load cell problem.
Check load cell cabling and junction box connections for corrosion or loose terminations, especially in dusty or humid plant environments.
Note whether the system uses a single load cell or multiple load cells summed together — multi-cell systems need each cell checked individually, not just the combined output.

Method 1 — Shunt Calibration

Shunt calibration simulates a known load electrically by switching a precision resistor across one arm of the load cell's bridge circuit, without physically applying any weight.

Useful as a quick verification that the electronics — indicator, cabling, junction box — are responding correctly and proportionally.
Fast and doesn't require test weights or stopping production for a physical load test.
Limitation: shunt calibration only verifies the electrical/electronic path. It does not verify the load cell's actual mechanical response to a real physical load, and it cannot catch mechanical issues like a bent load cell, misaligned mounting, or friction in the weighing structure. A system can pass shunt calibration perfectly while still weighing incorrectly under real material load.

Method 2 — Test-Weight Calibration

Applies actual certified weights to physically verify the load cell's response:

Zero the system with no load/material present, and confirm a stable zero reading.
Apply certified test weights in increments (e.g. 25%, 50%, 75%, 100% of expected working range) directly onto the weighing platform or via a calibration frame designed for the feeder.
Record the indicated weight at each increment and compare against the known applied weight.
This method verifies the complete mechanical and electrical chain — the load cell's physical response, the mounting, and the electronics together — which shunt calibration alone cannot do.

Method 3 — Dead-Load / Material Reference Calibration

Used when certified test weights aren't practical for the size of feeder/hopper involved (common on large weigh feeders):

Uses a known reference — such as a hopper's loss-of-weight over a measured time period, or a pre-weighed batch of actual process material — as the calibration reference instead of certified test weights.
Only as accurate as the reference itself — if the reference measurement (e.g. the hopper load cells providing the loss-of-weight figure) is inaccurate, the feeder calibration inherits that same error, even though the feeder itself may be functioning correctly.
Always verify the reference source is itself in good calibration before using it to calibrate another instrument against it.

Checking Individual Load Cells (Multi-Cell Systems)

On systems with multiple load cells summed together, an individual cell can be reading incorrectly while the combined output still looks plausible. Isolate and check each cell's output individually where the system design allows, rather than relying only on the summed total — a single bad cell in a multi-cell arrangement can be easy to miss if you only ever look at the combined reading.

Common Mistakes to Avoid

Relying on shunt calibration alone and assuming it verifies real-world weighing accuracy.
Not checking mechanical freedom (binding, friction, misalignment) before assuming an electrical/load cell fault.
Using an unverified reference (like an uncalibrated hopper) for dead-load calibration and not questioning the reference when results don't improve.
Only checking the combined output on a multi-cell system and missing a single faulty cell.
Skipping the zero check with no load before applying test weights.

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This is a general field procedure — specifics vary by feeder design, load cell type, and plant calibration standards. Adjust to your own SOP where needed.

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