Tait Controls main project for 2010 was the safety and reliability upgrade of four 25kg milk powder packing lines at Fonterra's Whareroa site.
Guarding was installed on each of these lines to restrict operator access, which is now only possible when air reservoirs have been dumped and the power cut to selected motors. Normal entry to the safe zones is triggered by 'entry request' buttons, now allowing the machinery to come to a controlled stop, which permits restart with minimum disruption.
A safety PLC controls and monitors the guarding, safety contactors, and air dump valves. These all have dual PLC inputs, which the PLC checks for 'discrepancy faults' (different states). Safety contactors and air dump valves all have dual PLC outputs to ensure fail-safe operation. Status of the safety zones and individual safety devices are shown on an HMI page, along with full diagnostics, allowing the operators to quickly resolve faults, resulting in less plant downtime.
A large portion of the line software was re-written in a more structured step logic style so that each part could be brought to a controlled stop. While this was being done minor issues with the previous software versions were addressed, and changes made to cope with hardware which had been upgraded to increase reliability. With all of these changes each line needed to be re-commissioned as powder became available.
The upgrades resulted in an increase from 18.75 to 20.25 tonnes of powder packed per hour.