A belt weigher’s zero is its empty-belt reading. When it keeps moving, something in the weigh area has changed: build-up, a dragging idler, the belt, the frame, or water in a junction box. Re-zeroing over and over just hides it. Find the cause, fix it, then zero.
This guide is about a zero that keeps changing. If the scale shows a flow rate on an empty belt, see empty-belt flow readings. For other symptoms, see common belt weigher faults.
How much zero movement is normal?
After a proper clean, a one-off zero change of around 1% is normal: you’ve just taken dead weight off the frame. A zero that keeps walking after cleaning and alignment needs investigating, not re-zeroing.
A new belt beds in over a week or two, so check the zero after the belt work and again once it has settled. Your integrator’s zero limit and auto-zero settings decide when it flags a problem, so check them in the manual for your model.
Who adjusts what. On our service visits we adjust the zero and span when the checks show it’s needed. Between visits, site should run a zero about every two weeks and after a big change in the weather. We recommend a service calibration every quarter so the scale keeps up with the seasons.
Is it drifting, jumping or wandering?
- Drifting slowly one way: usually material building up, wear, or moisture getting in between cleans.
- A sudden step: check what happened at that time: cleaning, belt work, an idler change, a power disturbance or a settings change.
- Wandering up and down: look at the belt, vibration, something touching the frame now and then, or a loose connection. Watch whether the pattern repeats with each belt revolution.
The pattern tells you where to look first. A step after belt work can be more than alignment, and a fault that shows up in wet weather isn’t automatically a failed load cell.
What do we check?
Work on or near a conveyor, or inside an electrical enclosure, needs isolation under your site’s procedures and trained, authorised people. If that’s not you, stop and call us on 1300 101 666.
- Build-up and carryback on the frame, the weigh idlers and the idlers either side. Where it sits changes how much it moves the zero.
- Weigh idlers: condition, wear, a seized or dragging roller, and alignment with the idlers either side, typically within about 0.3 mm. The exact target depends on the scale.
- Belt tracking and tension: is the belt running centrally and evenly through the weigh section? Take-up changes and belt work show up here.
- Frame and supports: anything fouling the frame, and loose or damaged mounts. Don’t loosen restraints to see what happens; they’re there for a reason.
- Load cells and wiring: water in the junction box, corrosion, damaged cable and loose terminals. See is it the load cell, the cable or the junction box?
- Settings: recent changes, auto-zero and filtering. The display isn’t the raw load cell signal, so check what the integrator is doing to it.
Why doesn’t re-zeroing fix it?
A zero captures the empty belt as it is right then. If the build-up later falls off, or the belt and frame behave differently under load, that zero is wrong again. Re-zeroing can’t fix a damaged load cell or a binding frame either.
Zeroing a clean, empty belt is normal routine. What isn’t normal is a zero that needs correcting every time, zero cycles that get rejected, or results that won’t repeat. Record the change, find the cause, and don’t widen the zero limit to make the alarm go away.
How do we track it down?
Save the existing settings and recent results first. Clean and inspect with the conveyor isolated. Never reach into a running conveyor, remove guards or open up electrical gear to chase a wandering reading.
Once the work is done, run the belt empty until it’s at normal operating condition, zero over whole belt revolutions, then repeat the zero to see if it holds. How long to run and how many revolutions to use depends on the model, so check the manual. Then decide whether the span, speed or a material test also needs checking before the scale goes back into service. See what zero, span and repeatability mean.
How does service history help?
Compare results taken the same way and in the same units, and note cleaning, repairs, weather, loading and settings changes next to the numbers. For the assets we maintain, AIMM keeps the service records, so we can see changes across visits. A pattern tells you what to inspect and when to service; on its own, it won’t tell you which part has failed.
When is repair or an upgrade worth it?
If the zero is still unstable after a proper clean and these checks, get it assessed. We look at the whole scale, repair where it makes sense, and recommend an upgrade when condition, downtime or unreliable figures make it worth it. Talk to us about replacement options, or see weightometer calibration and belt weigher servicing.
Frequently asked questions
How much zero drift is normal?
After a proper clean, a one-off change of around 1%. A zero that keeps moving after cleaning and alignment points to something mechanical, so call us rather than keep re-zeroing.
Why does the zero change after rain?
Usually wet build-up, water in a junction box, or the belt behaving differently when it’s wet. Re-zero after a big change in the weather, and if it keeps happening, get it checked. The weather tells you when it moves, not why.
Should I wait a week after a new belt before checking zero?
No. Check it after the belt work, then again once the belt has bedded in, usually a week or two. A new belt or splice also means re-measuring the belt speed and length, re-entering them and recalibrating.
How often should site zero the belt weigher?
About every two weeks, and after a big change in the weather. Zero on a clean, empty belt over whole belt revolutions.
Need a manual for your equipment?
Talk to us about manuals for your equipment. Send the make, model, serial number and software version (a photo of the label is fine) and we’ll help you find the right document.