Conveyor Controls

Conveyor controls are the system layer that decides when a belt may start, run, stop and interlock with upstream and downstream machines: motor control centres, PLC or relay logic, start-permit philosophy, sequence (upstream off before downstream, or the reverse), and the wiring of those decisions. Field devices still matter, but a blocked-chute probe is instrumentation, and a pull-wire along the walkway is pull-key hardware. This page is the logic, panels and permits. Tick the device categories as well when you need hardware and logic in one briefing.

Part of the Conveyor Knowledge Centre. Research the duty first, then request a quote when you are ready to brief suppliers.

A typical plant belt will not start unless pull-keys are healthy, alignment and speed switches are in a defined state, chutes are not blocked, and the downstream machine is running — or the reverse sequence on stopping. That cause-and-effect lives in PLC code or hardwired relays, presented on an MCC and often on SCADA. Brownfield South African plants mix generations of relay logic, old PLCs and new VSDs; quoting “controls” without naming the existing platform produces guesswork.

Start permits, emergency-stop reset (local, remote, or both), and whether a trip must lock out until inspected are policy as much as hardware. MHSA-aware underground systems and surface plants with different reset rules need that philosophy written down. Controls work also includes cubicle space, cable schedules, and whether the supplier must write software or only supply a bucket.

Belt starters (soft starters/VSDs) are power devices that the PLC commands. Instrumentation is the sensors. Pull keys are the e-stop lanyard system. Drives are the mechanical package. Keep those distinctions in the RFQ so an instrumentation technician is not asked to rewrite MCC sequence, and a PLC house is not asked to supply pull-wire hardware only.

Common applications

Controls jobs range from a single conveyor bucket to a transfer-house sequence. Common briefs:

MCC buckets and motor starters as a system — Not only the soft starter module, but how it sits in the board, protection, and isolation. Say if the MCC is existing or new.
PLC sequence and interlocks — Start/stop order across multiple belts, feeders and chutes. Provide existing PLC make if it must be matched.
Start-permit and E-stop reset philosophy — Who may reset, from where, and after which trips. This is often the real scope after an audit finding.
Brownfield integration — New conveyor into an old mill sequence, including SCADA mimics. Integration labour can exceed hardware — say supply-only versus full commission.

Industries that use this equipment

Mines and mineral processing plants run dense interlocking between crushers, feeders, belts and stockpile machines; sequence errors dump ore or idle a pit.

Cement, coal and ports need reliable start permissives across long galleries and ship loaders.

Food, FMCG and warehouses emphasise zone control, E-stops and guarding interlocks more than heavy rip detection, but still need clear PLC philosophy.

Underground coal and hard rock add certification and robust enclosures to the same logic conversation.

Specifications buyers should consider

The list below is a briefing checklist, not a datasheet. Exact ratings, dimensions and standards must come from the duty, existing plant records and the supplier quotation — do not treat generic web copy as a specification.

Scope: MCC hardware, PLC software, both, or cause-and-effect design only.
Existing PLC/SCADA/MCC makes and whether they are mandatory.
Number of conveyors and machines in the sequence, and battery limits.
Reset and permit philosophy in words (not a slogan).
Which field devices already exist versus must be supplied (then also tick Instrumentation or Pull Keys).
Starting method already chosen (DOL, soft start, VSD) so I/O and buckets match.
Standards or owner specifications if any; underground or hazardous-area notes.
Supply only, install, software, commissioning, and training.

Factors that affect selection

A controls house that will not touch field devices still needs a device list and I/O map.
Do not ask a pull-key supplier to write PLC sequence, or a PLC house to guess lanyard layout without a walkway drawing.
Starter hardware may be quoted under Belt Starters and still be commanded by this controls scope — say who owns the bucket.
Turnkey conveyor projects may wrap controls; use this category when controls are a separate package or a brownfield upgrade.
Nuisance trips are often set-point and sequence issues, not “bad sensors” — describe the symptom.

Common problems and failure considerations

Operators bypassing interlocks because sequence or set-points nuisance-trip the plant.
A new belt that can start against a blocked chute because permissives were never mapped.
E-stop that stops the motor contactor but not related feeders.
Software in a PLC the owner cannot support locally.
Split responsibility: electrical contractor, OEM and instrumentation each thinking the other owns cause-and-effect.

Maintenance considerations

Keep I/O lists and cause-and-effect as-built; they are the maintenance manual for controls.
After adding a sensor, update the trip philosophy so it is not an orphan alarm.
Test E-stop and permit chains on a planned interval under a safe procedure.
Do not “jumper” a trip without a recorded temporary waiver.
Coordinate VSD parameter changes with the PLC sequence so ramps and permissives still agree.

Questions buyers should ask suppliers

Hardware, software, commissioning — which are included?
Will you work on our existing PLC make, or propose a new controller?
Who supplies field devices and pull keys in your battery limits?
How will you document cause-and-effect and reset philosophy?
What site time do you need for I/O proving?
Are MCC modifications in this quote or a separate electrical contractor?

What to include when requesting a quote

Clear briefs produce comparable quotations. Include what you know, and mark estimates separately from measured values. Photos and drawings help more than extra adjectives.

Existing PLC/MCC/SCADA photos and makes.
Written start/stop sequence and what must not happen (dump, rollback, start against blockage).
Reset philosophy.
List of conveyors and related machines.
Whether Belt Starters, Instrumentation and Pull Keys are separate line items.
Owner standards, underground notes.
Commissioning window and whether production must continue around the board.

Related conveyor information

Related components: instrumentation, pull keys, belt starters, drives.

Guides: Types of Conveyor Systems, Industrial Conveyor Maintenance Guide, Choosing a Conveyor Supplier in South Africa.

Resources: How to request a conveyor quote, Conveyor maintenance guide, Conveyor systems in South Africa.

Frequently asked questions

Controls versus instrumentation versus pull keys?

Controls is MCC/PLC sequence, interlocks and start permits. Instrumentation is sensors such as alignment, speed, blocked-chute and scales. Pull keys are the emergency-stop lanyard hardware along walkways. A complete safety upgrade often ticks all three and states who writes the logic and who supplies the devices.

Can I tick Controls if I only need a soft starter?

If the job is only the power device, use Belt Starters. Use Controls when sequence, board changes, PLC code or permit philosophy is in scope. Tick both when a new starter must be integrated into existing interlocks.

Do you need our PLC program?

For brownfield work, yes if you can share it, plus an I/O list. If you cannot, say so and ask for a site survey. Guessing addresses from a one-line sketch is how sequences get quoted incomplete.

Is this the same as a turnkey conveyor project?

Turnkey wraps mechanical and electrical delivery of a working system. Controls as a category is the electrical/logic package, often on an existing conveyor. Use Turnkey Projects when you want design-to-commission of the machine; use Controls when the steel and belt stay and the brains need work.