Belt weigher terminology: a plain-English glossary

One machine, many names

Work around conveyors long enough and you will hear the same machine called several different things. They are all the same equipment: a scale built into a running conveyor that weighs material as it moves along the belt (see how a belt weigher works).

• Belt weigher is the name we use most.
• Weightometer is an older name that stuck, still common on mine sites.
• Belt scale and conveyor belt scale mean the same thing.
• Conveyor weigher turns up in specs and drawings.

You will also hear “weigher” or “weigh frame” used loosely for the whole system, even though the weigh frame is really just the mechanical part that carries the load onto the sensor. Whatever your site calls it, the job is the same. What follows is an A to Z of the words that come up around belt weighers, weigh feeders, tramp metal detectors and the scanners and gauges that sit alongside them.

A to Z of belt weigher terms

A/D count: Analogue to digital count: the raw digital number the integrator reads from the load cell before it is scaled into a weight. Useful in setup and fault finding, because it shows what the electronics actually see.

Accuracy class: A trade-measurement grading for how small a weigher’s error may be. There are four: Class 0.2, Class 0.5, Class 1 and Class 2, with Class 0.2 the tightest. The number is a grade, not the tolerance itself, so Class 0.5 does not mean half a percent. It applies to legal-for-trade weighing, not to the routine maintenance calibration we do to keep process weighers reading true.

As-found and as-left: As-found is the reading before we touch anything; as-left is the reading after adjusting. The gap shows how far the scale had drifted and what we corrected (see what happens during a calibration visit).

Auto zero (zero tracking): A setting that lets the integrator make small corrections to the empty-belt zero on its own while the belt runs. It keeps up with slow build-up, but a window set too wide learns a coated belt and bakes the error in, and a zero that has moved too far is refused with an alarm (see why a belt weigher reads wrong at low flow).

Bed roller and wing roller: A troughed idler set is usually three rollers: a flat centre roller with an angled wing roller each side, which lift the belt into a trough. Bed rollers are the closely spaced rollers under the loading point where material lands.

Belt cut test and material test: Two ways to prove a scale against a known amount of material. A belt cut test weighs by hand the material sitting on a stopped, measured length of belt and compares it with what the weigher recorded. A material test runs a known quantity across the scale instead (see belt cut tests).

Belt radar: See Volumetric belt scanner.

Belt scale: See Belt weigher.

Belt scanner: See Volumetric belt scanner.

Belt tracking: How well the belt runs centred on the conveyor. A belt that wanders rubs the structure, spills material and can disturb the weigh frame, so it is corrected during a service.

Belt weigher: The equipment we specialise in: a scale built into a running conveyor that weighs material as it passes. See the section above for its other names.

Belt width: The nominal belt width in millimetres (common sizes 600 to 1500 mm). It drives roller sizing, the trough shape and how much the belt can carry.

Billet (test weight): A steel bar of known mass, hung on or rested on the weigh frame to apply a set load during calibration. On a fully suspended frame it bears straight onto the frame, and it reads the same wherever on the frame it is applied. Where the weight acts through a pivot or lever, the load reaching the weigh idler is not the stamped mass and the difference has to be allowed for (see ETW).

Bin level radar (silo scanner): A radar sensor mounted in the roof of a bin or silo that measures the surface of the material inside, giving level and, with a scanning head, the volume and shape of the pile. Radar copes with the dust and build-up that defeat ultrasonic sensors. We supply iSilo bin level radar: see belt radar and safety products.

Build-up and carryback: Material that sticks to the belt, weigh frame or rollers; carryback is what is carried back past the discharge on the return side. Both add false weight and cause tare drift (see tonnes counting on an empty belt).

Calibration chain: See Test chain.

Capacity (t/h): The design throughput of a conveyor or weigher in tonnes per hour. It sets the top of the weighing range and feeds the span and load cell sizing.

CHPP: Coal handling and preparation plant, where run-of-mine coal is crushed, screened, washed and sized before it is stockpiled or loaded out. Many belt weighers sit on CHPP conveyors.

Chute blockage switch: See Tilt switch.

Conveyor belt scale: See Belt weigher.

Density gauge (nuclear density gauge): A gauge that measures how dense the material running through a pipe or chute is, without stopping to collect a sample. Most in mining put a small sealed radioactive source on one side and a detector on the other, and that sealed source is why moving, storing or servicing one needs radiation licensing. See what a density gauge is and density gauge troubleshooting.

Drift: A gradual, one-way change in a scale’s readings over time, not random scatter. A climbing tare or a slowly shifting span usually points to build-up, wear or a mechanical fault (see common belt weigher faults).

Effective test weight (ETW): The equivalent belt load a test weight actually produces once the frame geometry and weigh span are accounted for. On a fully suspended frame the weight bears straight onto the frame and the stamped mass is used as it stands. Where the weight is applied away from the weigh idler, the integrator allows for the difference through a factor set for that frame and calibration method, so the figure typed in is still normally the stamped mass. Check what your integrator is asking for before entering anything.

FRAS: Fire resistant anti static: a material rating for rollers, belts and parts used underground in coal mines, where components must not spread fire or hold a static charge.

Idler: A roller assembly that supports the belt along its length, usually three rollers in a troughing set (a centre roller and two wing rollers). Idlers off the weigh frame simply carry the belt.

Idler spacing: The distance between idler sets along the conveyor. Even spacing through the weighing area matters most, because uneven idlers change how the belt load sits on the scale (see Weigh span).

Impact flow meter (solids flow meter): A plate inside a chute that falling material strikes, turning the force of the impact into a rate in tonnes per hour and a running total. There is no belt, no speed sensor and no weigh frame, so its alarms and its calibration work differently to a belt weigher (see the Micro-Tech 9106 impact flow meter integrator).

Integrator: The electronic unit that turns the load cell and speed signals into flow rate and total tonnes. Common makes here include Ramsey, Thermo Fisher, Siemens Milltronics, Schenck, EMC, Web Tech, CST and Tecweigh (see Thermo Ramsey Micro-Tech servicing).

JSA: Job safety analysis: a short document written before a task listing each step, its hazards and the controls, signed off by everyone doing the work before it starts.

Junction box: The weatherproof box where the load cell and sensor cables join before the signal runs to the integrator. A damp or corroded box is a frequent cause of drift (see how a belt weigher works).

Legal-for-trade: A weigher approved and controlled for buying or selling material by weight, so its reading can settle a sale. Most calibration we do keeps process weighers accurate and is not legal-for-trade.

Lever ratio: On weigh frames that use a pivot or lever, the ratio between the load applied and the load that actually reaches the weigh idler. Fully suspended frames do not have one. Where it does apply it is worked out on site rather than read off a drawing, and it shifts with the slope of the conveyor, so it is not a single fixed number on a conveyor whose incline changes.

Load cell: The sensor that turns the weight on the weigh frame into an electrical signal. Most weighers use two, larger frames four. A failed or water-affected cell is a common reason a scale reads wrong.

Loss-in-weight feeder: A hopper on load cells that feeds material out at a set rate, working the rate out from how fast the hopper weight is falling rather than from material on a belt. Refilling pauses the measurement, which is why these run and fault differently to a belt weigher (see Micro-Tech 2104 and 9104 loss-in-weight feeder controllers).

LOTO and isolation: Lock-out tag-out: making the conveyor safe by isolating its energy, locking the isolator and tagging it, so the belt cannot start while someone is on it. Done before anyone goes near a weigh frame.

Low flow cutoff (zero drop out): A rate below which the integrator stops counting, so a small zero offset cannot invent tonnes on a nearly empty belt. Set too high, it throws away real material on a lightly loaded run (see why a belt weigher reads wrong at low flow).

Magnetic separator: A magnet over or around the belt that continuously pulls tramp iron out of the material. It removes the metal, unlike a tramp metal detector, which only detects and alarms (see Tramp metal detector).

mV/V: Millivolts per volt: how a load cell’s sensitivity is rated, the signal it gives at full load for each volt of excitation (a typical cell is 2 or 3 mV/V).

NMI: The National Measurement Institute, the Australian body responsible for trade measurement. Its rules apply to legal-for-trade weighing, not to routine maintenance calibration, which is a practical accuracy check.

Nuclear density gauge: See Density gauge.

R-Cal (electronic calibration check): An electronic span check. With the belt running empty, the integrator unbalances the load cell bridge with a reference signal and reads the result, so the cells themselves are in the loop rather than just the display. It is a comparison, not a verdict: the figure is logged when the system is set up and later checks are read against that baseline, with a shift of around half a percent the usual trigger for a full calibration with weights. Zero the scale before you run one. It takes minutes, but it applies no real load, so it says nothing about build-up, a worn roller or a bind, and it cannot see the frame itself flexing. Not every integrator has the hardware fitted for it, even where the software is already there (see belt weigher calibration methods).

Repeatability: Whether the scale gives the same reading for the same load, time after time. Good repeatability (little scatter between repeat tests) is the sign of a mechanically sound weigher (see zero, span and tolerances).

Roller: A rotating tube on a fixed shaft that supports or shapes the belt. We record roller sizes as: diameter (outer size), face (barrel length the belt runs on), back-to-back and total length (the mounting dimensions), shaft diameter, and across flats (the flat-to-flat size of a hex shaft end).

ROM (run of mine): Raw material straight from the pit or face, before crushing or processing. A ROM conveyor carries this feed and often holds the first weigher in the chain (see CHPP).

Silo scanner: See Bin level radar.

Solids flow meter: See Impact flow meter.

Span: The sensitivity setting that fixes how the load on the belt relates to the displayed weight. Set with a known reference (test weights, a test chain or material), it is the main “how much” adjustment (see zero, span and tolerances).

SPC: Statistical process control: charting calibration results such as tare and span over time against warning and alarm limits, so a slow drift shows up as a trend early (see Drift).

Speed sensor (tacho, encoder): The device that measures belt speed, usually a wheel on the belt driving a pulse generator, also called a tacho or (for digital pulses) an encoder. A slipping sensor throws the totals out (see belt weigher speed sensors).

Spiral cage: The most common belt weigher speed sensor on Australian sites: an open, cage-style wheel that sits in the gap between the carry and return runs and bears up against the underside of the carry belt, turning with it to drive the speed signal. The open spiral sheds sticky material that would otherwise pack on and change its effective diameter. It lifts the carry belt by 10 mm or more, so it is mounted well clear of the weigh frame, where that lift cannot pull the idlers out of line. Its bearings are the usual wear point (see belt weigher speed sensors).

Splice: The join where the two ends of a belt meet in a loop, vulcanised (moulded) or fastened with clips. A splice passing over the weigh frame can cause a small repeating bump in the readings.

SWMS: Safe work method statement: a more detailed safety document than a JSA, required for high-risk work, setting out hazards and step-by-step controls. Often required alongside a permit.

Tare (zero): The empty-belt reading, the weight the scale sees with the belt running but no material on it; zeroing sets this baseline. A tare that drifts up usually means build-up, not real load (see zero, span and tolerances).

Test chain: A calibrated chain laid on the belt through the weighing area to imitate an even belt load, used to set span where billets or a material test are not practical. It applies a known weight per metre, and it has to be long enough to reach past the fixed idler beyond each end of the weigh frame, then secured so it cannot lift off the belt anywhere between them, under the least tension that is safe to handle. Because it loads the frame through the belt it exercises more of the system than static weights do, though it still cannot reproduce the belt tension of a fully loaded belt. Also called a calibration chain. We hire one out with its current certificate: see test weights, chains and billets.

Tilt switch (chute blockage switch): A switch mounted on a chute or bin that tips when material builds up against it, stopping the feed before the chute plugs. Older Ramsey units are still everywhere on Australian sites, many of the oldest mercury filled, and we can supply replacements: tell us the model number.

Totaliser: The running count of total tonnes the weigher has measured, like an odometer for material. Sites read it for production and reconciliation. It normally only counts up, and that is how integrators usually leave the factory, but some can be set to take tonnes back off when the rate goes negative. So a total that has moved backwards is worth checking against the setting before anyone calls it a fault or a tampered display.

Trailing arm: A speed sensor design where a measuring wheel on a pivoting arm rides the belt, like a surveyor’s wheel, keeping firm belt contact so the speed reading stays true. Arms working on the return side are held down by their own weight; those bearing up on the carry side are spring loaded, as are the heavier duty versions. Wheel size matters more than the mounting: a small wheel picks up material build-up and starts reading long, so a large diameter wheel, or a sensor driven off a pulley, is the better choice where belt speed accuracy is critical (see belt weigher speed sensors).

Train load out: The conveyor and bin system that loads product into rail wagons, often with a weigher controlling how much goes into each wagon. Usually one of the more closely watched weighers on site.

Tramp metal detector (TMD): A coil-based detector around or under the belt that senses stray metal (tramp iron, broken tools, digger teeth) and alarms or stops the belt to protect crushers downstream. Unlike a magnetic separator it detects only, it does not remove the metal. Makes you will see on Australian sites include Oretronic, Eriez, Tectron, Detec and ADS (see metal detectors on mining and quarry conveyors).

Trough angle: The angle the wing rollers tilt the belt up from flat (commonly 20, 35 or 45 degrees). A deeper trough carries more material but changes how the load sits on the weigh idler.

Verification: In trade measurement, the formal check and marking that a legal-for-trade instrument meets the rules. It is separate from the routine accuracy calibration we do on process weighers (see NMI).

Volumetric belt scanner (belt scanner, belt radar): A laser or radar unit mounted over the conveyor that measures the profile of material on the belt and, with belt speed, reports the volume passing a point. It does not weigh: turning volume into tonnes needs a bulk density figure, and that figure moves with moisture and material. Where tonnes are accountable a scanner sits alongside a belt weigher rather than replacing it (see belt weigher vs volumetric scanner).

Weighbridge: A large platform scale that weighs a whole truck or wagon at once, sitting still, rather than material moving on a belt. Different equipment from a belt weigher, though sites often cross-check the two.

Weigh feeder: A short conveyor that both weighs material and controls how fast it is fed, dosing it at a set rate into a mill, blender or process. It pairs a belt weigher with a speed-controlled drive.

Weigh frame (weigh module): The mechanical assembly that carries the weigh idler and passes the belt load onto the load cell, also called the weigh module, scale carriage or bridge. Its condition and cleanliness are central to accuracy.

Weigh idler: The idler, or idlers, mounted on the weigh frame whose load is actually measured. The conveyor’s other idlers just support the belt; only the weigh idler sits on the scale.

Weigh span: The length of belt the scale weighs, set by the weighing idlers and those either side of them. It combines with belt speed and the load cell reading to work out flow, a key calibration figure.

Weightometer: See Belt weigher.

Zero drop out: See Low flow cutoff.