My belt weigher shows no speed, or the total has stopped climbing

This guide covers a lost or wrong speed signal. For sensor types and wiring, see the belt weigher speed sensors guide. For unstable rather than absent readings, see erratic totals, and for other symptoms, common belt weigher faults. Until a speed fault is fixed and re-checked, don’t use that weigher’s tonnes for reconciliation.

What does a lost or wrong speed do to my tonnes?

A zero speed makes the rate zero, so the total stops. You can run a full belt and record nothing. Those tonnes can only be estimated afterwards from run hours and a typical rate.

A speed that’s a few per cent out is worse, because nothing looks broken. Speed multiplies load one for one, so 2% off the speed is 2% off every tonne, while the rate follows the feed and the daily totals sit in their usual range. Example only: on a belt doing 1,000 t/h, a sensor reading 2% slow reports 980 t/h, and the missing 20 t/h only shows up at reconciliation. See how the t/h calculation works.

What causes it, in the order we find it?

1. The wheel or cage on the belt. It lives in the dirt and the weather. Bearings go rough, then seize, and the wheel stops: the classic dead reading. Short of that, it wears smooth and slips on a wet belt, the arm or spring sags until contact is lost, or material packs on until it rides on a crust. Slip is the one to watch: the number stays believable while tonnes go missing.
2. The mounting. A loose bracket or an arm knocked out of position leaves the wheel crooked, riding light or off the belt. A shaft-mounted sensor has its own version: it reads its pulley correctly while the belt slips on that pulley.
3. The cable and terminations. Chafe where it crosses steel, crush damage, terminals vibrated loose, water in the sensor junction box, rodent damage in a cable tray. These go intermittent before they fail, so a speed that drops out and comes back points at the wiring.
4. A mismatched sensor after a swap. The output type and voltage have to suit the integrator’s input, and the pulses per revolution setting has to match the sensor. Too few pulses at your belt speed makes the speed move in steps or misbehave at low speed.
5. The target, on a shaft or proximity arrangement. A missing, bent or loose target drops pulses and reads low. Set the gap too tight and the target eventually strikes the sensor.
6. Interference counted as pulses. Drive noise on an unshielded run, a shield earthed at both ends, or a sensor cable beside power cable adds counts the belt never made. This one reads high. See protecting belt weigher electronics.

How do you check it?

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.

Start at the integrator. Watch the speed display while the belt is visibly running. A moving belt with zero on the display is a speed signal fault, and recalibration won’t touch it. Rule out the simple things first: some integrators hold the speed at zero while a run permissive or remote input says the conveyor is stopped, and some read zero below a minimum speed, which matters on a variable speed conveyor that’s crawling. Check the manual for your model.

Then look at the sensor from a safe position outside the guarding. On a wheel or cage you can usually see whether it’s turning. A wheel standing still under a moving belt is your answer. A wheel turning normally while the display reads zero puts the fault downstream: cable, terminations, input or settings.

The timed check. Measure a known length between two fixed points, mark the belt while the conveyor is isolated, then time the mark between the points once it’s running again, from outside the guarding. Repeat it a few times and average. Divide the metres by the seconds and compare that with the displayed speed.

More than about 2% off the measured speed needs investigating. If they agree, the speed input is fine and the problem is elsewhere. If the integrator reads correctly but the control room total isn’t moving, the fault is in the link, not the belt weigher: see getting belt weigher data into your PLC or SCADA.

What can site check?

From a safe position with the belt running:

• Is the wheel or cage turning, and is a bearing running rough?
• Is the belt tracking away from the wheel?
• Does the fault follow wet weather, or one drive speed?

Once the conveyor is isolated, locked out and proven dead, trained people can clean the wheel or cage, check the bracket and arm are tight and the spring still holds, look for water in the sensor junction box, and follow the cable for damage.

Grease the speed sensor bearings monthly. On our frames, they and the billet weight bearings are the only grease points. It’s worth keeping a spare wheel and bearings on the shelf.

Replacing the sensor? Our USR speed sensor mounts on the tail drum or as a trailing arm. It has multiple outputs, so one sensor can feed two belt weighers, or a belt weigher plus the conveyor underspeed. We’ll confirm it suits your integrator’s input first. See our speed sensors.

Need a manual for your equipment?

For a speed fault, also note the speed sensor make and model, and the pulses per revolution or wheel diameter set in the integrator.

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?

Call us on 1300 101 666 when the wheel turns but the reading doesn’t, when a new sensor changed nothing, when the timed and displayed speeds are more than about 2% apart, when the total climbed with the plant stopped, or when the fault comes and goes.

We prove the chain rather than adjust the number: sensor turning and in contact, pulses reaching the integrator, settings matching the sensor fitted, speed timed against the belt. Only then do we calibrate and re-check, and a belt cut test settles any argument left about tonnes. If the sensor has failed, we’ll tell you straight whether to repair it or replace it.

We supply parts for the major belt weigher brands: a genuine part where it’s available, or a suitable alternative, with compatibility confirmed and the part identified on the quote.

Frequently asked questions