ATSys has upgraded the telemetry system and hardwired safety circuits resulting in a new AS4024.1 compliant, high integrity safety system.


 


Challenges:

  • Existing hardware at end of life
  • Existing installation not compliant with Safety of Machinery AS4024.1
  • No diagnostic information available to operators
  • Low integrity data transfer

Solutions:

  • Allen Bradley GuardLogix PLCs
  • Allen Bradley POINT Guard I/O
  • Electrical Monitoring hardware system upgrade
  • Design and Installation of DLR fibre network

Results:

  • High integrity safety over ethernet devices
  • Additional diagnostics
  • Automated Proof Testing via SCADA

Background

Dalrymple Bay Coal Terminal (DBCT) undertook a project from 2014 to 2015 to upgrade the emergency stop system and associated devices along six of their conveyors and replace them with an AS4024.1 compliant PLC and remote I/O system. The improved performance of the new remote I/O system was additionally leveraged to replace the existing telemetry system on the conveyor. The new system interfaced with safety devices such as pull wires and motor contactors, and non-safety devices such as belt drift switches and hooters along the length of the conveyors. The conveyors ranged in length from 1.4 to 3.8 kilometres. ATSys successfully delivered the upgrade whilst introducing many benefits to the operation of the site, overcoming challenges encountered throughout the project. This report discusses several of these challenges, and the benefits that DBCT were able to realise.

 

Upgrade Challenges

The existing Dupline telemetry system provided a low integrity transfer of data, extremely limited diagnostic information to operators and was susceptible to communication dropouts and spurious trips. Furthermore, the installation did not conform to the current recognised standards for machine safety.

 

Allen Bradley GuardLogix PLC

To rectify the above, the existing Allen Bradley ControlLogix PLC had a CPU upgrade to a GuardLogix Safety PLC. Shown above, the GuardLogix Safety PLC and POINT Guard Safety I/O allowed for an AS4024.1 compliant safety system whilst additionally providing a high level of diagnostic detail of the system including network, module and I/O point status.

The inclusion of the GuardLogix Safety Partner into the existing ControlLogix rack was a potential challenge for DBCT. As the existing PLC communicated with many other PLCs throughout the site, it was important that the upgrade would not require additional works to be conducted on every other PLC simultaneously.

ATSys investigated how the Primary and Secondary networks communicated and the best method of altering the Conveyor PLC's expansion cards to ensure that the upgrade did not cause site wide downtime. During the roll out, the PLC was successfully changed without affecting the other PLCs and ATSys provided a non-critical procedure to update the other site PLCs at a time suitable for the maintenance engineers.

Point IO module in panel

 

Improved Diagnostics

The existing SCADA screens provided only a limited fault status for each of the safety devices, such as the conveyor trip wire inputs. The safety instructions included with Rockwell's RSLogix 5000 (Such as the DCST: Dual Channel Input Stop with Test) were used exclusively to interrogate the status of all of the Allan Bradley Safety Point I/O . These safety functions had not previously been used by DBCT and provided greater visibility and more diagnostic information quickly to the operator. Each safety I/O point was also configured to perform safety diagnostic checks and report faults to the system as required.

SCADA screens were also created so that the status of the individual Point I/O could be easily checked. Pre-existing hardware SCADA screens were appropriately updated for the new hardware, ensuring that existing site standards were adhered to.

 

DLR Fibre Network

ATSys designed and installed a new Fibre Network in a Device Level Ring (DLR) configuration to ensure redundancy and highly reliable communications.

DLR Fibre Network displayed in SCADA

A new DLR SCADA display was added as part of the project and highlights the exact location of a fault  in the ring if it occurs. This level of diagnostics has allowed the site maintenance personnel to respond to, analyse, and rectify faults quickly and efficiently. The DLR was achieved by running a single multi-mode fibre cable along the 1400 metres of the coneyor and looping in and out of each remote I/O adapter head, skipping alternate nodes on the way out and connecting to them on the return path using different cores.

Additionally, a new Ethernet overview display was added to SCADA, designed to be consistent with the existing DeviceNet displays.

 

Proof Testing

An important component of the AS4024.1 compliance is regular proof testing of all safety devices to ensure they remain in working order. ATSys went to considerable effort to ensure that the proof testing process would not be onerous on the individuals involved, automating a large portion of the process and delivering a SCADA screen that drives the process for the operators.

Dialogue box for grace period

Proof testing of all devices was required at intervals not exceeding one year, and tracking of these intervals is kept seperately for each safety device. The date of the last proof test and time until the next proof test is required are displayed on the Proof Testing SCADA display. Appropriate warnings and alarms ensure the operators are alerted to an impending proof test due date, and a grace period feature was included allowing a safety device to be used for a 7 day period along with a permanent warning. Once the grace period expires, the safety device is locked out from use until the proof test has been completed.

 

Security and Reliability

At the end of the commissioning process, the Safety Task on the Allen Bradley GuardLogix PLC was locked and the PLC was set to Run mode to prevent unauthorised access.

FactoryTalk View security was installed to ensure that only authorised users had access to open the PLC code.

 


 

 

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