Part 6, Chapter 3 — Checkweighers Part 6, Chapter 3 · Weighing Systems Mastery Checkweighers: In-Line, High-Speed Weighing for Quality Control Every other system in this book weighs continuously or in batches. A checkweigher weighs hundreds of individual, discrete items per minute — each one, on its own, in a fraction of a second. Live · Items Passing at High Speed, Pass/Reject Decision WEIGH CELL SECTION REJECT POINT Start Production Line Stop 0 Items Weighed 0 Rejected — Running Average Start the line — items pass through the weigh cell section at high speed, each one weighed and checked against a 500g ± 5g target in a fraction of a second. Every weighing system covered earlier in this book handles either continuous flow (Part 2's feeders) or a single vessel's...
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Weigh feeder calibration procedure
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Part 3, Chapter 3 — Test Weight (Chain) Calibration Procedures, Step by Step
Part 3, Chapter 3 · Weighing Systems Mastery
Test Weight (Chain) Calibration Procedures, Step by Step
A calibrated chain, draped exactly across the weigh span, simulates real distributed material load far better than a single weight sitting in one spot ever could.
Live · Chain Test Calibration, Step by Step
Step 0 of 6
Procedure Progress
1.0000
Span Calibration Factor
Click "Next Step" to walk through the complete chain test calibration procedure.
With preconditions confirmed (Chapter 2) and zero verified stable, span calibration is what actually teaches the system the relationship between a real known load and its own reading. The chain test method is the standard approach on most belt weigh feeders.
Confirm zero is still stable immediately before beginning — a genuine re-check, not an assumption carried over from earlier.
Drape the calibrated test chain across the FULL weigh span length (and typically a short distance beyond each end), so its distributed weight simulates real material loading far more accurately than a single point load would.
Enter the chain's known total weight (per its own certification, weight per unit length × span length) into the calibration routine.
Compare the displayed reading against the known weight — the system calculates a span factor adjustment needed to make the two match exactly.
Apply the calculated span factor and verify the displayed reading now correctly matches the chain's known weight.
Remove the chain and re-verify zero — confirming the zero point wasn't disturbed by the calibration process itself, and that the system returns cleanly to its baseline.
Why a Chain, Specifically, Rather Than a Single Test Weight
A single concentrated test weight placed at one point on the belt loads the weigh span's structure differently than material genuinely distributed along its entire length — depending on the weigh span's exact mechanical design, a point load and an equivalent distributed load can produce subtly different readings even for the identical total weight. A calibrated chain, laid along the FULL span length, much more closely replicates how real material actually loads the structure, making it the preferred method specifically for span calibration (as opposed to the simpler point-weight method sometimes used for basic zero or sanity checks).
Checking Linearity, Not Just a Single Point
A single chain test at one weight value confirms accuracy AT that specific load level — it says nothing about Chapter 4 (Part 1)'s nonlinearity across the rest of the range. Where genuine linearity verification matters (particularly for legal-for-trade or tight-tolerance applications, Part 7), repeating this same procedure at two or three different simulated load levels — using chains of different certified weights, or combining multiple chain sections — checks whether the calibration holds consistently across the load range, not just at one convenient point.
Check Your Understanding
Why is a distributed test chain generally preferred over a single point test weight for span calibration?
Answer: A distributed load along the full weigh span more closely replicates how real material actually loads the structure — a point load can produce a subtly different reading than an equivalent distributed load, depending on the weigh span's mechanical design.
Why does the procedure end with re-verifying zero after removing the chain, rather than considering the calibration complete once the span factor is applied?
Answer: To confirm the calibration process itself didn't disturb the zero point, and that the system returns cleanly to its baseline — a shifted zero after "successful" span calibration would mean something was disturbed during the procedure.
CHAPTER RECAP
The chain test procedure: verify zero, drape a calibrated chain across the full span, enter its known weight, apply the calculated span factor, then re-verify zero
A distributed chain load more accurately replicates real material loading than a single point test weight
A single-point calibration check doesn't verify linearity — multiple test levels are needed where genuine linearity verification matters
Re-verifying zero after removing the test chain confirms the calibration process itself didn't disturb the baseline
Fault Log · Field Report Schenck Weigh Feeder — Zero and Span Drift, Two Different Root Causes Plant: Cement | System: Schenck weigh feeder, belt scale, hopper load cells | Downtime: None Symptom A Schenck weigh feeder started showing both zero drift and span drift at the same time. Two separate accuracy problems showing up together made this a two-part investigation from the start — zero and span errors don't always share the same root cause, even when they appear together. Investigation — Zero Drift Started with the load cell loop and mechanical side of the belt scale: Load cell loop — checked the full loop, cleaned the load cell area. Idlers/rollers — checked the rollers for wear or misalignment. Belt tracking — with the belt empty, noticed it was drifting to one side. Zero was being tared in that empty, drifted position. Once material loaded onto the belt, the belt tracked back closer to center — meaning the zero reference had been tak...
Fault Log · Field Report Zirconia Oxygen Analyzer Reading Maximum O2 — Not the Cell, a Rusted Outlet Plant: Cement | System: Zirconia oxygen analyzer, sample extraction system | Downtime: None Symptom The zirconia oxygen analyzer started reading maximum oxygen — pegged at the top of the range rather than tracking the actual process value. A reading stuck at maximum on a zirconia cell usually means the cell is seeing something close to ambient air instead of process gas, which points straight at a sample delivery problem before you even think about the analyzer itself. Investigation Started at the sample path, from the process side inward: Probe, extractor filter, sampling line, pump — checked the full sample path from the probe through the extraction filter and sampling line, including the sample pump. Performed a leakage test across this section. All found ok. Panel-side tubing and membrane filter — checked all tubing inside the panel along...
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