Level I Automation Systems

Level I systems are usually considered to be the first level of control above the actuators and sensors in the field ("Level 0"), the classical example being the programmable controller (PLC).  Level I systems should be rugged enough to be placed close to field devices without normally requiring environmental enclosures, and should contain I/O suitable for industrial application.

The word "usually" is used above because modern technology has blurred the distinction between Level 0, Level I, and Level II systems.  There are some sensors and actuators that incorporate a significant amount of intelligence, thereby pulling Level I functions down into Level 0.  More prominent recently have been the human-machine interface (HMI)/supervisory control and data acquisition (SCADA) packages that run on PC platforms.  These systems can either interface to Level I, or directly to Level 0 (via a third-party I/O sub-system), and provide color graphic process-mimic displays and set-point control (which are typically Level II functions), and in some cases can even perform feedback controller functions at moderate sampling speeds.

IPACT believes that HMI/SCADA systems are not wholesale replacements for either traditional Level I or Level II systems, but can be profitably applied to a variety of automation functions from both levels, depending on the particular application and the package applied to it.  One of the roles that these systems fulfill well is that of a flexible color graphic operator interface connected to a "traditional" Level I system (PLC).

This document will cover IPACT's experience with both traditional Level I systems and HMI/SCADA packages.

What industries has IPACT provided Level I and HMI/SCADA systems to?

IPACT has provided Level I and HMI/SCADA systems to customers in the food, petrochemical, metals, auto, and other durable goods manufacturing industries.

 

Which manufacturers' Level I products has IPACT worked with?

IPACT has cultivated expertise in Allen-Bradley, Modicon, and GE Fanuc, and has provided systems using PLC equipment from each of these manufacturers.  This includes Allen-Bradley's ControlLogix processors as well as Modicon's Concept IEC-1131 programming environment.  We have expended significant effort to come "up to speed" with these developments in order to be ready to help our customers benefit from these advances in technology.

In addition, IPACT has worked with Reliance and Westinghouse Level I systems.

"Cultivating expertise" to IPACT means more than just studying manuals or attending a few training sessions.  IPACT has its own PLC equipment resources to support developing our customer's projects as well as advancing our own proficiency.  To that end, IPACT owns Allen-Bradley PLCs including SLC, PLC-5, and ControlLogix processors and supporting software, Modicon PLCs including Compact, 785-E, and Quantum processors and supporting software (including Concept), and GE Fanuc PLCs and supporting software.

 

What automation and control functions has IPACT provided within Level I systems?

Classical Feedback Control

These functions have included PID control of temperature, position, speed, etc.  To IPACT, classical control means more than just inserting a PID block in PLC logic, and letting the customer cope with sampling, scaling, and tuning problems.  It means understanding the process that is to be controlled, and providing the best possible control solution considering the required control performance and stability. Control system design is an engineering discipline.  IPACT doesn't just write PLC logic.  We are engineer control solutions.

Custom Feedback Control

Standard PID control is adequate for some applications but not for others.  IPACT has the expertise to determine what applications require something different and to design the required method.  These have included non-time-based control schemes, adaptive control systems, gain scheduling schemes, characterizing system components, and non-linear control schemes.

Motion Control

Numerous manufacturers make motors, amplifiers, and drive systems specifically tailored to precisely controlling and coordinating motion.  IPACT has experience with several of the most widely utilized motion control systems, and has used them in applications ranging from six-axis precision positioning of processing equipment in the metals industry to five-axis coordination of product and processing equipment motions in the food industry.  Several of these systems were staged and tested at our facilities rather than at the customer site.

Product Batch Transfer Interlocking and Sequencing

Level I systems provided by IPACT are responsible for transferring batches of product between processing sub-systems which are running asynchronous to one another.  The automation is responsible for moving batches from one sub-system to the other safely and in minimal time.

Product Metering

IPACT Level I systems meter fine dry ingredients, coarse dry ingredients, wet ingredients, low viscosity liquids, and high viscosity liquids at various flow rates and to various precisions, using weight measurement, loss-in-weight measurement, and integrated flow measurement.  A common feature of all these systems is overshoot compensation ("pre-act") and prediction using digital filtering techniques.  IPACT has found overshoot prediction digital filters to provide superior performance compared to more common techniques (such as "average of the last  n").

Testing

IPACT has supported both in-production testing (measurements taken and analyzed from normal production activities) and test-stand testing from Level I systems.  One of these testing applications utilized a special Level I system (not a PLC) which took process measurements at approximately 2000 samples/second, and analyzed that data to determine product quality and process safety (i.e. the Level I could shut down the process based on dynamic analysis of the measurements.)

Scheduling

Some innovative scheduling functions have been supplied by IPACT within Level I systems.  These functions are applied in facilities that produce a series of batches of mixed product in rapid succession.  Each batch includes up to four ingredients out of a possible ten.  The Level I scheduling system looks ahead in the batch schedule as far as necessary to keep all otherwise idle conveying and weighing equipment busy and produce the series of finished batches with a minimum of delay time between them.

Pneumatic Conveying

IPACT has provided Level I automation systems for bulk handling systems that use air to move product, and is therefore familiar with the concepts and methods typically used in pneumatic conveying.

HMI Support

Most of the Level I systems provided by IPACT have included support for some type human-machine interface, from simple two line ASCII displays to template-oriented monochromatic terminals to color graphic CRTs.

Maintenance Support

Maintenance personnel (and occasionally operators) typically need access to the low-level control of field devices.  IPACT Level I systems have supported their needs in several ways, such as Level I "maintenance modes" which allow individual control of devices from an HMI while no automatic functions are being performed, and "hand-off-auto" functions which allow manual control of field devices while automatic functions are proceeding.

 

What automation and control functions has IPACT provided within HMI/SCADA systems?

Control Systems

IPACT has used HMI/SCADA packages as feedback controllers for applications in process industries.  These systems make continuous adjustments to the processes at a rate of ten samples/second based on measurements of the controlled variable and setpoints provided from an operator, schedule/recipe, or a higher level system. In addition to controller functions, these systems performed a variety of alarming, statistical quality control, historical data collection, and reporting functions.

Operator Interfaces

IPACT has applied HMI/SCADA packages to provide operator interfaces on several large manufacturing processes (approximately 90 screens per application). These interfaces included color graphic process mimic screens, process alarms, and operator entry.

Supervisory Control and Data Acquisition Systems

In several systems supplied by IPACT, virtually the full capability for the PC-based package was used to supply a complete supervisory control and data acquisition system that played the role of a classical Level II system, interacting with PLCs below and Level III computers above, while providing operator interfaces on the plant floor.  The SCADA systems were responsible for short term scheduling and product tracking, sending setpoints to PLCs controlling various parts of the process, alarming, reading recipe data from Level III and sending production information back up to Level III.  In addition, all manual control of plant equipment was done via the SCADA system operator interfaces; the operators had virtually no hand operated controls for running the process.  The system supported maintenance as well by presenting numerous historical trends in fashion that made tuning and troubleshooting easier.

Process Simulation

An innovative - perhaps unique - application HMI/SCADA systems by IPACT has been as simulation systems.  Automation systems require testing before installation, and these tests are much more effective if the Level I system has a simulation of the real process to control.  As many of the HMI/SCADA packages interface to Level I local area networks, they come into consideration as simulation tools if the process is not high speed.  This is especially true if a database and mimic screens have already been developed for the process of the package.  In this case, another node can be added to the LAN which uses the existing database and modified versions of the process mimic screens to provide a simulation of the real process.  IPACT has used this strategy very successfully for several large automation systems.