Process control at IHF is standardized on Allen Bradley's PLC family, a combination of PLC-5s, SLC-5s, PLC-2s, and SLC-100s and -150s.
"Most of the PLCs are used in stand-alone configurations, with a single processor running a machine," notes Mark Reich, automation engineer for IHF. Some PLC-5s are also used for line control, with one controller running a line incorporating numerous machines. Operator interfaces are PC-based using Visual Basic for supervisory systems.
IHF first explored simulation software because of delays it was facing in starting up production processes. "We were having integrators writing our PLC code and our entire operator interface code," notes Reich. "However, when they would bring it into the plant, start-ups could take months until we could get a system working the way we desired." Delays, occurring in both individual machines and in line control, were frustrating, costly and unacceptable.
After repeated instances of delays, Reich began applying SST's PICS Simulation in an effort to address the problems. PICS is an I/O simulator for testing PLC-based control systems and for training system operators. It allows the manufacturer to quickly create dynamic models on a PC that duplicate the process parameters, and provide the PLC with feedback. To the PLC, there is no difference between controlling the PICS model and an actual process.
IHF piloted PICS on one of its filling lines. "This was a case where start-ups lingered for months," says Reich. "We bought the PICS package and apart from the integrator who wrote the PLC code, quickly developed a simulation. We then took the code and started simulating the process."
It was a very positive development, according to Reich. "Operators had a chance to come down and 'run the machinery' before it was commissioned, quickly picking out elements related to on-floor operation that affected the process--things the integrator or supervisors did not have the native knowledge to identify."
This helped speed the process refinement and operators liked the idea of seeing the operator interface before having to run it on the floor. "On new projects, the use of PICS greatly diminishes start-up time 20 to 30 percent using simulation software," says Reich. Meat grinding is a representative example of how the process works, notes Reich "First, all the inputs and outputs and their effects are determined. Typically, discrete operations are considered first, then analog control. Once laid out, code is put into the simulation to duplicate the process.
This exercise troubleshoots the PLC code and determines whether it is working to expectations. Are things turning on when they need to turn on? Are they turning off on time? Are the proper indications being given? Does the operator have the right information? The use of PICS confirms performance before the line is commissioned, resulting in faster implementation, smoother operation, and greater profitability, according to Reich.
SST, 50 Northland Rd., Waterloo, ON Canada N2V 1N3 Tel.: (519) 725-5136; Web site: www.sstech.on.ca