A crushing plant control system upgrade replaces the relay logic, ageing programmable logic controllers (PLCs) and unsupported networks that many quarries and recyclers still rely on to start, stop and protect their plant. These systems have often been modified many times, are poorly documented, and depend on spares and expertise that are increasingly difficult to obtain.
When the control system becomes the risk
The warning signs develop gradually:
- Faults take hours to find. Without accurate drawings, tracing a fault through a relay panel or a field network depends on whoever installed or last modified it.
- The plant is started by hand. Conveyors and crushers are started individually from local stations because the automatic sequence no longer works reliably.
- Interlocks have been bypassed. Links and jumpers added to keep the plant running remove the protection the interlocks were installed to provide.
- No visibility. The supervisor learns about a stoppage by radio, and there is no record of what tripped or why.
None of these stops production on its own. Together they mean that a single component failure can cause an extended outage. An ABB survey found that unplanned downtime costs a typical Australian industrial business about $349,000 per hour, and that 69% of businesses experience unplanned outages at least monthly. A quarry’s figure will differ, but the direction is the same.
Why older crushing plant controls fail
Relay logic was the standard for crushing plants for decades, and many relay panels have been extended far beyond their original design. Later plants used early fieldbus networks such as DeviceNet to connect motor starters and drives. These networks work well when maintained, but they rely on specific interface cards and configuration tools that are no longer widely supported, and a single failed device can take down an entire network segment.
Control Global describes a United States crushing operation that ran its plant manually for about seven years after its DeviceNet-based control system became too difficult to operate and support, before upgrading to a modern PLC system. The circumstances are specific, but the pattern of working around a control system instead of replacing it is common.
What a crushing plant control system upgrade includes
The upgrade replaces the control layer while retaining sound plant equipment. A typical scope includes:
- A new PLC and input/output (I/O) system in a purpose-built panel, or panels distributed around the plant
- A start sequence that brings the plant up from the stockpile conveyors back to the primary crusher, and a stop sequence that clears material before each machine stops
- Conveyor interlocks, zero-speed (belt slip) monitoring, chute blockage detection and pull-wire monitoring
- An operator interface showing plant status, running hours and the first-out alarm for every trip
- Secure remote access for authorised supervisors and support staff
How the start and stop sequence works
- 1
Check permissives
Before starting, the PLC confirms emergency stops are healthy, guards are closed and no chute is blocked.
- 2
Start downstream first
Stockpile and screen conveyors start first, then secondary crushers, then the primary, so material always has somewhere to go.
- 3
Monitor while running
Zero-speed and blocked chute signals stop the affected section and everything feeding it, recording which device tripped first.
- 4
Stop in order
A controlled stop halts feed first and lets each conveyor clear before it stops, leaving the plant empty and ready to restart.
What the upgrade is worth
The value lies in shorter fault-finding, fewer nuisance trips, restarts without manual intervention and a plant that no longer depends on one person’s knowledge. A first-out alarm alone can reduce the time to identify a trip from many minutes to seconds.
Alternatives to a full upgrade
- Keep repairing the existing system. Lowest immediate cost, but spares and expertise continue to decline and the risk of a long outage grows.
- Replace failed parts with used spares. Buys time, but used parts carry unknown history and do not address documentation or interlock problems.
- Like-for-like replacement of the network. Restores function but keeps the same limitations.
- A large systems integrator. Well suited to greenfield plants. For an existing quarry plant, a scoped upgrade avoids the overheads of a large integrator.