Usually because a setting is doing exactly what someone set it to do. The deadband stops the rate and the totals inside a window around zero, and automatic zero tracking re-zeroes the scale once the rate has sat low for a set number of belt revolutions, so whatever is on the belt becomes the new zero. Neither raises a fault. Check the lowest rate your plant really runs against those two stored values first.
This guide sits under our WP20 and WP25 fault codes and calibration guide, which has the calibration walkthrough and the message list. We’re an independent service company, not a Tecweigh dealer or agent.
Why would a Tecweigh read low with nothing on the screen?
As far as the processor is concerned, nothing is wrong. A load cell fault or a lost speed signal shows a message; a deadband wider than your feed just shows zero rate and a still total. Both settings leave the factory at zero, so if either is set, someone entered it, and finding one doesn’t rule out the other. When totals read low but the scale calibrates cleanly, we check these two first.
What does the deadband do to your tonnes?
It’s a window either side of zero. While the rate sits inside it, the display shows zero rate and nothing is added to the totals. It isn’t just a display filter: the totalising stops too, and the control room sees what looks like a healthy scale on an empty belt.
It exists to null out the apparent weight of an imperfect empty belt: thickness variation, splices, repairs and damage. See why a belt weigher reads a flow rate on an empty belt. The WP25 manual names a second use, keeping small trickles such as carry-back out of the total. The processor can’t tell a dribble from a genuine light feed, so a deadband set to swallow carry-back also swallows your slow shifts.
Set it last. The WP50 manual puts the deadband after both the zero and the span, to settle whatever empty belt fluctuation is left. Set before a span, it hides an uncalibrated zero and ends up far too wide.
Where the empty belt genuinely swings both ways, there’s a better tool. A count-down setting lets negative rates decrement the total, and both manuals recommend it for very long belts, or belts with greatly varying empty loading that would otherwise need a large deadband. The swings then cancel out across the shift.
What does automatic zero tracking do, and when does it bite?
When the rate falls below the tracking rate and the set number of track revolutions has passed, the processor runs an automatic zero. Whatever is on the belt at that moment becomes the new empty belt reference. It’s meant to cancel build-up, and on a clean, well fed belt it earns its place.
It’s two settings, not one. Both the tracking rate and the track revolutions have to be above zero. Leave the revolutions at zero and it just forces the rate to zero inside the tracking band, with no zero taken: a deadband in all but name. The US revision of the WP20 manual says totalising stops too.
The makers’ advice is to leave tracking off while a system is first set up, and off where the running rate is typically low. Where it’s used, start the tracking rate at around 5% of the normal running rate, and set the revolutions so the belt empties completely before the zero starts (the older manuals ask for at least five minutes of tracking).
Example only: on a belt that normally runs 800 t/h, 5% is 40 t/h, which is near empty. But if the plant spends half the shift trickling at 30 t/h, the belt lives below that threshold and the scale re-zeroes onto a loaded belt again and again.
Tracking can’t tell build-up from a light feed. It also hides developing build-up and fouling, which get corrected away instead of showing as zero drift until they surface late as a big number. See why a belt weigher zero drifts.
Why shouldn’t tracking run where the belt can be restarted remotely?
The WP50 manual says automatic zero tracking isn’t recommended where material flow can be restarted while an automatic zero is taking place. If it happens, the scale takes its zero on a loaded belt and under-reads every tonne afterwards. There’s no alert, no log entry and nothing to find later.
The zero runs over whole belt revolutions, so the window is minutes, not seconds. On a mine or quarry, belts are routinely started from a control room by someone who can’t see the scale, so we raise this wherever tracking is on. The caution is only in the WP50 manual; the WP20 and WP25 manuals don’t carry it, although those processors do exactly the same thing.
What does your processor call it, and can it tell the plant?
| Processor | Deadband | Zero tracking | Plant signal |
|---|---|---|---|
| WP20 | No separate parameter. Tracking with the track revolutions at zero acts as one. | A zero tracking notice in the mode window. It clears on any key press or when the rate rises. | No relay option. The serial status character does report a tracking cycle. |
| WP25 | A separate dead band parameter, with no status message. Inside it, the scale looks exactly like an empty belt. | A zero tracking notice, as on the WP20. | A relay can operate when a tracking zero shifts the zero by more than a set percentage of full scale. |
| WP50 | A rate in deadband alert: zero rate, no totalising. | An alert that the track revolutions have elapsed and an auto zero is about to run, but only if a relay is set for tracking and the track revolutions are above zero. | A relay can energise when tracking exceeds its limit. With the fieldbus card, both states are published to the control system as status flags. |
For the WP50 fieldbus side, see getting WP50 faults into the PLC and getting belt weigher data into your PLC or SCADA.
If a weigher is allowed to change its own zero, tell the plant every time it moves the zero by more than a set amount. On a WP25 or WP50 that’s a relay and a short wiring job.
How do you tell this from a genuine low-flow problem?
Compare the lowest rate your plant genuinely runs, in the processor’s units, with both stored values. If you ever run below either, that’s your answer.
If not, the fingerprints differ. A zero offset still counts, just wrongly: it’s a fixed amount of apparent load, so the percentage error grows as the rate falls. A deadband counts nothing below its threshold, so the total is right at full rate and short after a shift of light running, start-ups and tails. See why a belt weigher is only wrong on a light belt and what zero, span and repeatability mean.
If the rate is unsteady rather than low, the WP50 and WP20 troubleshooting sequences both say to disable tracking first, then increase the rate damping. See why belt weigher totals are erratic. And rule out an open interlock: on a WP20 or WP25 it disables the rate, the total and every output.
What should the two settings be on your conveyor?
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.
- Order first. Both settings come after a completed calibration, never before.
- Deadband: below the lowest rate the plant genuinely runs (our rule, not a manual figure). If carry-back is the problem, fix the carry-back.
- Tracking: off on a genuinely low-rate feed and during first set-up, as the maker recommends. Where it’s used, both values above zero, the tracking rate around 5% of the normal running rate and the revolutions long enough for five minutes or more of tracking. If the belt can be started from anywhere the person at the scale can’t see, turn it off.
- Record both as found and as left, every visit. Neither leaves a trace anywhere else. We keep them in AIMM, our asset management system, with the zero and span figures, and our calibration reports carry the settings as well as the results.
Need a manual for your equipment?
The deadband and tracking settings are in the weigh processor manual, a different book for the WP20, WP25 and WP50. Editions matter here: the US WP20 manual says totalising stops when tracking runs with zero revolutions and the Australian edition doesn’t, and only the WP50 manual carries the restart warning.
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.
When should you call us rather than change the numbers yourself?
- The totals read low and either setting sits above the lowest rate you run.
- Tracking is on and the belt can be restarted from a control room. Sort it out this week, not next quarter.
- Tracking is firing regularly. A zero that keeps moving is build-up, wear or fouling reporting itself.
- Someone wants to widen the deadband to settle an unsteady rate. That hides a zero problem instead of fixing it.
When we come out we check the whole weigher, not just the two settings. See how we service Tecweigh belt weighers, or call 1300 101 666.
Frequently asked questions
What does rate in deadband mean on a Tecweigh WP50?
The rate is inside the deadband window, so the WP50 shows zero rate and isn’t totalising. On an empty belt that’s correct. With material running, the deadband is set wider than your feed.
Should I turn auto zero tracking on or off?
Off during first set-up and where the normal running rate is low, as the maker recommends, and off wherever the belt can be restarted out of sight of the scale.
Does my WP20 have a deadband setting?
Not as a separate parameter. On a WP20 the deadband is tracking with the track revolutions left at zero, which forces the rate to zero inside the tracking band.