How do I determine the right capacity and minimum weight?

Size capacity just above the real load with safety for dynamics; then run MSA to establish the minimum weight where repeatability and uncertainty meet your window. Operate well above that floor or split micro/macro dosing.

What’s the single biggest cause of weighing error in tanks?

Mechanical shunting—hard piping, side loads, frame twist. Use flex connections, check rods, proper mounts, and isolate vibration; filters can’t fix bad mechanics.

Do I need dynamic filtering on every scale?

Use the least filtering that achieves stability without lag. Validate coefficients in OQ and lock them under Document Control. One-size-fits-all filtering is a red flag.

How often should scales be calibrated?

Risk-based intervals proven by history and usage. Critical steps merit more frequent verification. All devices must be in calibration status at execution—MES should block if not.

Can I rely on a tank scale for micro-gram additives?

No. Use lab-grade or EMFC micro stations for small actives and dose concentrates when needed. Tank scales serve macro ranges; combining both on one device invites error.

How do I prove weighing control to an auditor?

Provide IQ/OQ/PQ, calibration/MSA, corner tests, filter parameter records, SPC on hit-to-target and noise, and complete eBMR/audit-trail evidence tying weights to devices and users.

Load Cells & Weighing SystemsGlossary

Load Cells & Weighing Systems – Foundation of Gravimetric Control

This topic is part of the SG Systems Global regulatory & operations glossary.

Updated October 2025 • Gravimetric Control, Accuracy & Data Integrity • Manufacturing, QA/RA, Automation, Maintenance

Load cells convert force into a trustworthy number. Everything else—the controller, the HMI, the dashboard—is theater unless the weighing system is designed, qualified, and governed. In factories that live on grams and tonnes, gravimetric weighing sets recipe truth: what you actually charged, blended, packed, and shipped. Miss the fundamentals—minimum weight, mechanical isolation, temperature drift, filtering—and you’ll chase phantom problems in SPC, argue at release, and leak margin in rework and over‑give. The blunt truth: bad weighing turns good processes into noisy myths.

“If the scale lies, the batch record lies. Fix the physics before you fix the spreadsheet.”

TL;DR: Engineer weighing as a system: right cell type and capacity, rigid and isolated mounts, sensible wiring/grounding, temperature/EMI defenses, and validated filtering. Operate above minimum weight; do math in mass first; push targets from governed recipes through a validated MES with interlocks, audit trails, and live SPC. Keep devices in calibration status; prove capability with MSA/TMV. No shadow spreadsheets; no “tap the hopper” fixes; no out‑of‑status scales on critical steps.

1) What Weighing Systems Cover—and What They Do Not

Covers: the complete load path (structure → load cell → junction/summing → indicator/ADC → controller), mounting hardware, piping/flex connections, electrical integration, environmental controls, and the logic that turns weight into setpoints for Weigh/Dispense, Micro‑Ingredient Dosing, Macro Dosing, checkweighing, and packout.

Does not cover: wishful accuracy claims that ignore minimum weight, poor installation, or unqualified environments. Weighing is physics + governance; no amount of software decorations rescues a bent frame or a vibrating mezzanine.

2) Legal, System, and Data Integrity Anchors

Weights used for regulated manufacturing and labeling land in your e-records. Keep software under Part 11/Annex 11 with CSV/GAMP 5 controls, unique users (UAM), and immutable audit trails. Devices must be qualified (IQ/OQ/PQ) and kept in calibration status. Records live in the eBMR with governed retention. Where net content is tested, expect alignment with TNE rules and label math—no “almost right” weights on consumer product labels.

3) Anatomy of a Weighing System

A reliable system has: (i) a rigid, stable support structure; (ii) the right load cell (single‑point, shear beam, compression canister, S‑type tension); (iii) mechanical hardware (mounts, bearings, bumpers, check rods) that supports load but blocks side forces; (iv) compliant piping/flex connections to prevent mechanical shunting; (v) shielded cabling with sense lines; (vi) summing/junction box with trim where multi‑cell; (vii) high‑resolution ADC/indicator; and (viii) control logic in SCADA/MES. Miss any piece and the number on screen becomes fiction.

4) Load Cell Technologies—What to Use, Where

Strain‑gauge beams/canisters. Workhorses for tanks, hoppers, platforms; robust and economical. Single‑point cells. Designed for small platforms; excel at corner load insensitivity. S‑type. Tension/compression for hanging applications. Electromagnetic force compensation (EMFC). Lab‑grade balances with excellent resolution and short‑term stability—ideal for micro work. Pick technology by load range, environment, sanitation (IP/NEMA), and dynamics—not by catalog gloss.

5) Capacity, Resolution & Minimum Weight

Capacity is not a bragging right—it’s a trade‑off. Oversizing kills resolution and minimum weight. Define minimum weight (the lowest mass that meets repeatability/uncertainty goals) from trials and MSA. Operate at least 20× above the scale noise floor for critical steps; if you can’t, split doses or upgrade hardware. Don’t mix 5‑gram actives with a 5‑ton tank scale and expect miracles—use a micro station and post‑blend, or dose concentrates upstream with precision micro controls.

6) Accuracy Drivers—Nonlinearity, Hysteresis, Creep

Load cells are not perfect springs. Expect nonlinearity (curve vs. straight line), hysteresis (up vs. down differences), and creep (time‑dependent change under constant load). Temperature adds drift in zero and span. Counter with (i) good mechanics; (ii) stable temperature; (iii) short dwell times at setpoint; (iv) filtered cutoff logic; and (v) periodic zero checks. Validate these in OQ/PQ and lock parameters under Document Control.

7) Mechanical Integration—Load Path or Noise Path

Bolted frames that rack and twist, rigid hard‑piped connections, and side loads will shunt force around the cell. Use flex connectors in all product lines, expansion joints to decouple thermal growth, and anti‑torsion hardware. Level platforms; avoid friction points; set bumpers to protect cells without carrying normal load. If forklifts or mezzanines transmit vibration, isolate the base or move the scale. Physics first, filters second.

8) Multi‑Cell Platforms—Cornering & Summing

Large platforms and tanks use multiple cells. Match capacities; wire via junction boxes with trim; perform corner/section tests; and record adjustments in maintenance logs. For digital cells, trim in software but document changes with e‑signatures in the audit trail. A platform that reads different weights in different corners is a liability, not an instrument.

9) Electrical Design—Noise is a Design Choice

Use 6‑wire cabling (with sense) to compensate voltage drops; keep cable runs short; segregate from VFD power; ground at a single point; and shield. Choose high‑resolution ADCs with stable excitation. For washdown or harsh zones, specify sealed junction boxes and IP‑rated cells; route cables away from steam lines. Lightning and surges are real: protect with proper bonding and surge suppression. Bad wiring makes brilliant algorithms look stupid.

10) Environment—Temperature, Washdown, EM & Static

Control temperature swings with Temperature Mapping; prevent condensation on connectors; specify IP ratings for washdown; and manage static with bonding/ionization, especially on micro scales. Monitor ambient conditions with Environmental Monitoring. If you can feel the draft or the heat plume, the scale can “feel” it too—shield or relocate the instrument.

11) Dynamics & Filtering—Cutoff Without Lag

Agitation, powder pour spikes, and splashing demand filtering that smooths noise without delaying cutoff. Prefer validated moving‑window or digital filters tuned in OQ. For dosing steps, implement fast → dribble transitions and end‑of‑flow compensation based on material behavior. Filtering is a controlled parameter: store coefficients and versions under Document Control and review in periodic performance checks.

12) Calibration & Verification—Evidence, Not Faith

Calibrate with traceable standards and representative loads. For tanks, use substitution (known test weights or water draw) and verify at multiple points up and down. Record linearity, repeatability, and corner loads. Lock intervals and status in Calibration Status. Mid‑run checks (zero and span checks) should be routine for critical steps; out‑of‑tolerance means impact assessment before release—not “note and proceed.”

13) MSA/TMV—Measure the Measurement

Run MSA to quantify repeatability/reproducibility; run TMV on checkweigh and net‑content methods; use ISO/IEC 17025 labs for reference comparisons. If R&R eats your window, the process isn’t “variable”—your scale is. Fix hardware or split the operation between micro and macro stations with appropriate windows.

14) Weigh Modes—Static, Dynamic, GIW & LIW

Static platforms suit manual dispense; dynamic checkweighers verify pack weights; gain‑in‑weight and loss‑in‑weight systems (see GIW/LIW entry) automate batch and continuous dosing. Don’t force static scales to do dynamic work—design for the flow regime you actually run. Bridge weighing errors show up later as mass‑balance gaps and yield variance.

15) Tare, Containers & Net—Simple, Then Strict

Gross − Tare = Net seems trivial until you change container lots mid‑run or let operators type tare. Govern tare by lot with scans; forbid free‑text entries; and store tare histories under Document Control. For variable containers (e.g., totes), measure and store tare at receipt and verify at use. Labels must consume the same net used for disposition—no parallel math.

16) Warm‑Up, Zero & Drift—Respect Device Physics

Load cells and electronics need warm‑up. Encode start‑up checks; auto‑zero within tight, governed limits; and trend zero drift as a health indicator. If zero moves with ambient changes, your isolation or temperature control is weak. Don’t bury drift in “operator retraining”—fix the cause or expect recurring deviations.

17) Hazard & Hygiene—Right Hardware for the Zone

Specify intrinsically safe or purged indicators where required; choose stainless/IP69K for caustic washdown; and plan for cleaning validation (Cleaning Validation). Hygiene hardware that bends under load is not “food safe”—it’s unreliable. Validate that cleaning doesn’t waterlog junction boxes or wick into cables.

18) Integration—Make Systems Do the Arithmetic

Bind device IDs and status to steps in the MES, ingest weights via SCADA, present setpoints on the HMI, and block execution on status failures. The WMS stages lots with eligibility checks; label verification prevents misconnects. Every critical weight lands in the eBMR with who/what/when/which device, not on paper slips that disappear at audit time.

19) SPC/CPV—Trend the Instrument, Not Just the Process

Use SPC to track hit‑to‑target, scale noise (σ at empty), zero drift, and end‑of‑flow compensation error. Quantify capability with Cp/Cpk and roll into CPV. Instrument SPC finds problems before batches do. If your charts never drive decisions, you’re decorating walls, not controlling risk.

20) Finance Tie‑In—Bad Weighing Shows Up as Cost

Over‑give from sloppy cutoffs and under‑fills from drift hit margin and brand. Quantify over‑give cost and tie it to scale performance. Connect weighing to mass‑balance closure and yield variance. It’s easier to fund a better micro balance when Finance sees the monthly loss in black and white.

21) Common Pitfalls & How to Avoid Them

Oversized scales. Capacity chosen for “headroom” ruins resolution. Right‑size or split micro/macro.
Hard‑piped tanks. Rigid connections shunt force. Install flexes and expansion joints.
Shared login HMIs. No attribution, no compliance. Enforce UAM.
Unvalidated filters. Tuning by feel creates hidden lag. Validate and lock coefficients.
Out‑of‑status devices. Running critical steps on expired calibration invites rework. Block in MES.
Spreadsheet setpoints. Move math into validated systems with audit trails.
Ignoring environment. Drafts, vibration, static: treat them like process variables.
No cornering. Multi‑cell platforms must be tested and trimmed—every time after service.
“We’ll fix it at release.” You won’t. Physics you ignore upstream punishes you downstream.

22) Metrics That Prove Control

Minimum‑weight margin vs. smallest target on each station.
Scale noise index (σ at empty) and zero drift per shift.
Corner error (%) on multi‑cell platforms after service.
Hit‑to‑target error (macro/micro) and cutoff overshoot distribution with Cpk.
Out‑of‑status blocks captured by MES and time‑to‑resolution.
Over‑give cost (per SKU) and mass‑balance closure at batch close.
Audit‑trail review health (late entries/edits) for weighing steps.

Good metrics provoke action—hardware changes, parameter updates, supplier escalations. Vanity metrics just keep PowerPoint employed.

23) What Belongs in the Weighing System Dossier

Device list with capacities/IDs; structural drawings and load paths; mounting and isolation details; electrical schematics and grounding; filter algorithms/versions; IQ/OQ/PQ and calibration records; MSA/TMV reports; corner/section tests; temperature/EM records; MES/SCADA/HMI integration mapping; audit trails; deviations/CAPAs; SPC/CPV charts; and approvals/effective dates under Document Control.

24) How This Fits with V5 by SG Systems Global

Device‑tight execution. The V5 platform binds load cells and indicators to steps, verifies status at runtime, pushes setpoints/windows, and blocks work on identity or status failures.

Governed math & records. UOM conversions, filters, and cutoff logic live centrally; every weight and adjustment lands in the eBMR with user/device IDs and full audit trails.

Quality & traceability. Live SPC/CPV surface noise, drift, and overshoot; V5’s WMS and EPCIS events tie weights to lots for end‑to‑end genealogy.

Bottom line: V5 turns weighing from tribal craft into governed automation—predictable for Finance, defensible for QA, and boringly reliable for Operations.