Fonterra sites label manufactured product with a cypher code, representing the manufacture date. Normally production runs are part of a continuous process which last the best part of a day, so the cypher shows the day when theproduction began, even if it continues past midnight. However, operations at Canpac are different to most Fonterra sites. The filling of bins, cans, and sachets is a batch process, with production runs varying from a couple of hours to more than a week. Usually the cypher code is replaced with a Unit code, which reflects the day of filling, and changes in ingredients.
Traditionally the day of filling corresponds to a calendar day, which meant that a short job which ran over midnight would produce product with two different Unit codes, even if the input ingredients did not change. Due to sampling and documentation requirements associated with the change in Unit code a great deal of time was wasted, to the point where it was more efficient to wait until midnight before starting one of these jobs.
Tait Controls were asked to modify the control systems so that day of filling represented 24 hour periods from the use of the first powder for a job. This change meant that the Unit code better resembled the cypher code allocated at other sites, and resulted in large savings and much improved effiency for small jobs.
The PLC changes required for these savings were not extensive, but were technically challenging. Canpac did not want 24 hour periods to vary, even if there were problems or changes in the PLC code, so Tait Controls chose to work with the internal PLC clock rather than discrete timers. This involved division of 64 bit numbers, using 32 bit functions, but meant that accurate times could be maintained even if the PLC was stopped or a new program downloaded (provided that record of job start times was maintained).
TCS (NZ) Ltd manufactured and supplied large 24 character Ethernet message displays for each production line. These were used to display a 24 hour count down for each running job, so that operators all knew when 24 hour periods were coming to an end. Other information was also displayed – job numbers, coding requirements, and status information when jobs were not running – all of which contributed to further improvements in effiency.