IMPLEMENTATION OF ISA S88.01 STANDARD INTO AN AUTOMATED PROCESS

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1 IMPLEMENTATION OF ISA S88.01 STANDARD INTO AN AUTOMATED PROCESS G. OPREA Valahia University of Targoviste, Doctoral School of Engineering Science - Electrical Engineering, 35 Stancu Ion Street, , Târgovişte, ROMANIA gabi_bvx@yahoo.com Abstract. S88 Batch Control Standard has been developed under the auspices of the ISA (the Instrumentation, Systems, and Automation Society) and is the appropriate Standard to apply in many Batch Process Control or Automation projects. The S88 standard enables clear and concise transfer of information between different disciplines, specifically the Process Engineer and the Automation Engineer. The standard breaks down 'process areas' into 'process cells', 'process units', 'equipment modules' and finally 'phases'. Using these smaller 'blocks' the URS (User Requirement Specification), FDS (Functional Design Specification) and ultimately the final control software, are constructed in a logical 'easy to follow' way. Keywords: process, areas, cells, units, equipment modules, phases. 1. INTRODUCTION The ISA Batch Control standard has had a major impact on the way batch process automation is done today. It has influenced everything from the way control systems are built to the way project requirements are written and has simplified and reduced the cost of batch control automation along the way [1]. S88 defines Recipes, which describe products and how those products are produced. Recipe procedures reside on a PC, while the programming code running the production equipment resides in the PLC (programmable logic controller) or DCS (distributed control system) residing within the equipment [2]. When it comes time to make a product, the manufacturing requirements defined by the recipe and its procedure are linked to the required equipment. The recipe phase within the PC batch server communicates with the equipment phases via a set of protocols held in the PC. These protocols define the states the equipment may function in, e.g. idle, active, pause, stop etc, and the possible transitions between states. A Phase Logic Interface (PLI) resides in the PLC or DCS system to enforce these transition protocols and communicate back and forth with the PC. The fundamental difference between traditional control and control as outlined in S88 is that S88 adds control of procedure and a level of coordination control necessary to keep multiple procedures sorted out. The concepts that are spelled out in terms of a batch manufacturing environment are consistent regardless of whether the control is provided manually or automatically. It treats control as a function that causes equipment to do the things necessary to make a product no matter how that control is achieved. Manual control is best or quite appropriate in many cases; automatic control is better in others. S88 works with either case, or both. It is based on the premise that whether a function is controlled manually or automatically it is the function that is important. This is particularly important in modern manufacturing approaches where there is usually the need for smooth integration of manual and automatic control activities. Few plants actually run all night with the lights out and people are a long way from being obsolete. 2. CONTROL PHILOSOPHY AND S88 STRUCTURE From the side of the control system the complete plant is divided up into single control modules, phases and recipes. With these control modules and phases the complete plant with all its instrumentation is defined. This structure follows the S88.01 architecture [3]. At any time the state of the complete plant with all the equipment will be visualized on the various PC-screens. Motors, valves, limit switches will change colours depending on their state. The analogue values are displayed as a number and in a trend. 2.1 Control modules A control module is controlling a single equipment part. The available control modules are: valves (On/Off valves or proportional valves), motors (fix speed and variable speed), analogue sensors (temperature, pressure, flow, weight, etc.), digital sensors (proximity switches, safety switches, etc.), PID control (for temperature, flow, pressure, etc.) and counters (for dosing via flow meters) [4]. On the SCADA system each of these control modules will be displayed by a corresponding symbol. For each control module a faceplate can be opened for additional information. This faceplate gives also the possibility to adjust parameters such as monitoring times, PID parameters, thresholds, etc. A service mode for authorised users is available to operate an actor in a service mode or set substitute values for a sensor. In the next example (Figure 1), is described the specifications of an equipment module control. 16

2 ISSN Scientific Bulletin of the Electrical Engineering Faculty Year 13 No.4 (24) uses the vacuum pump, plus a couple of valves and the pressure transmitter [5]. The phases can be operated in manual and automatic mode. The manual mode can be used for the commissioning of the single phases as well as for trouble shooting. In manual mode the operator is responsible for the entering of the correct set points and for the starting and stopping at the correct time. A production is normally carried out in automatic mode, where the set points for the phases and the sequencing are specified in the control recipes. Some of the mentioned phases are static, meaning that they need to be switched off. In this case the start and a stop phase are available. Other phases are non static; they switch off automatically after e.g. having dosed the required quantity. Common to all phases is that the phase will be paused when a control module of an equipment part which is used by the phase has created an error. E.g. a valve does not reach the requested position, motor trips out, fault on a sensor, etc. A phase in pause will automatically deactivate all equipment parts which are used by this phase. Meaning the valves will be closed and the motors will stop. A paused phase may also pause another phase. This is the case, when the running signal from one phase is one of the permissive for another phase. 2.3 Phase control panels Phase control panels are boxes with the phase reference number followed by the phase description. They are the operational steps through which the production process goes. Figure 2. Sample phase control panels Figure 1. Equipment module control specifications Inputs are indicated in a prescribed format on top of the picture, outputs are shown on the bottom and in the central part the processing which is necessary is described. Any other equipment module control should be described in the same manner. 2.2 Phases A phase is a combination of some of the control modules, which has to be operated together to achieve a specified result. The phase pressure control for example The panels will change color, (Figure 2) depending on the status of the phase it refers to: - Clear Phase not active; - Green Phase active; - Salmon Phase currently paused; - Red Phase stopped either in alarm or by operator action. By selecting the phase control panel a pop-up (Figure 3) will appear on screen which contains all the relevant data for that phase. It also contains the manual operator control soft buttons for that phase. The information and available functions within a phase control panel vary from phase to phase. In the phase control panel pop-up section all available parameters are listed. The section is split into to 3 parts: 17

3 - Set points: These parameters, such as the required pressure or temperature are typically changed more frequently. They can be used in a recipe at different stages of the batch with different values. If a phase is running in manual mode the set points for the manual mode will be used. If a phase is running in automatic mode, the set points from the recipe will be used. - Plant specific data: These parameters cannot be changed from recipe to recipe. The parameters can only be changed by persons with a special access level. - Actual values: These parameters cannot be changed; they display the actual values for different variables. Figure 4. Phases flow chart For each of the 3 main process steps, process 1, process 2 and process 3, individual control recipes are defined. These recipes contain all the required information to control the process. This includes times, speeds, product ingredients, temperatures, weights and so on. The control system will handle the download of the correct control recipes according to the master recipe at the right time into the several process units. 2.6 Master recipes A master recipe contains the control recipes for the different process steps. For each final product a master recipes needs to be defined. To start a production of a specified product the corresponding master recipe has to be loaded. The system then will download the correlated control recipes for the 3 process steps into the different process units. 3. PLANT CONTROL SYSTEM AND OPERATOR INTERFACE Figure 3. Phase control panel pop-up and,,actual popup 2.4 Transition condition In case the plant is operated in automatic mode by running a recipe, the system steps on to the next phase in the sequence when this transition condition for the running phase is fulfilled [6]. For example when the required amount is dosed, the required runtime is elapsed, the value for temperature or pressure is reached, etc. 2.5 Control Recipes A combination of the above mentioned phases, put together in form of a flow chart (Figure 4). A recipe consists of information about the set points for the individual phases as well as about the sequence in which the individual phases has to be carried out [7]. S88 defines hierarchical recipe management and process segmentation frameworks, which separate products from the processes that make them. The standard enables reuse and flexibility of equipment and software and provides a structure for coordinating and integrating recipe-related information across the traditional ERP, MES and control domains. The control system downloads the control recipes at the required time according to a master recipe. A master recipe will exist for each of the final products to be produced. Editing of the recipes can only be carried out by authorized persons via password protection. To start production of a specified product the corresponding master recipe has to be loaded. The operator selects this master recipe as an order from the order control screen on the SCADA system. When the order is started the system will download the required control recipes for the 3 process steps into the different process units. The operator then starts the available batches for this order. The system will then start processing the batch. 18

4 ISSN Scientific Bulletin of the Electrical Engineering Faculty Year 13 No.4 (24) 3.1 Plant control The complete control system consists of 3 main functional elements: the Process control system, the SCADA system and the PLC [8] The process control system The process control system is responsible for optimizing the different process phases. It allows the creation of recipes in form of a flow chart. These recipes are then used to control the individual phases required to make up the desired product [9], [10]. The required number of batches is calculated automatically. This calculation is done every minute and takes into account any amounts already produced and the remaining material in the plant SCADA System The SCADA (Supervisory Control and Data Acquisition) system is the part of the control system responsible for giving the operators the visualization of the equipment and processes (Figure 5). This is achieved through the different screens displayed on the HMI (Human Machine Interface the touch screen PCs) [11]. - The visualization of the equipment; - The overview of the Batch process and status; - The alarm and message handling and recording; - User interface for manual intervention. All the screens can be used by means of a mouse/touch screen or keyboard. Each site will locate the SCADA screens appropriately so for information please refer to your sites local appendix for details. Access to all screens is possible from any of the SCADA units however password protection is applied to certain maintenance and higher level functions such as batch and recipe modification PLC The PLC (Programmable Logic Controller) is from the Siemens S7-400 range of industrial automation controllers. The PLC monitors all the signals from the sensors and controls all the plants actuators (valves, switches motors etc). Based on the algorithms within the program it takes the recipe, which it receives from the process control system and controls all the single control modules, all the phases and the sequencing of the recipes. The PLC continuously communicates with the SCADA system and the Process control system to read commands and send status information. The SCADA screens show information which has been communicated via the PLC [12]. 3.2 Communication with ERP system The production network is separated from the plant network where the ERP system (SAP) is located. The whole data transfer between the control system and ERP will be managed by the PLC (Figure 6). Therefore the PLC has for each communication partner a separate network module at share the same memory to read/write each other s parts of data blocks that need to be defined. Figure 5. SCADA screenshot From these SCADA screens the operator can monitor and control the different processes. The errors or warnings from the plant and process are displayed on the SCADA screens and the system also logs all alarms and messages for future reference. This is useful in the event that several faults occur at once, as it saves the operator having to make notes of the alarms for the maintenance teams. The system also logs all events and analogue values from the plant such as temperatures. These analogue values can then be displayed as a graph. This graph can be viewed in real time as well as looking at historic data. The main features of this SCADA system are: Figure 6. Communication between networks 3.3 Production orders ERP system will transfer all orders that are planned to be fulfilled in a reasonable plan time range. An order from ERP contains very compressed information. This information contains following data: production line, set 19

5 amount of product [boxes], amount per boxes [kg], best before offset, planed start-up date and time, SKU (stock keeping unit). 4. CONCLUSION The fundamental difference between traditional control and control as outlined in S88 is that S88 adds control of procedure and a level of coordination control necessary to keep multiple procedures sorted out. The concepts that are spelled out in terms of a batch manufacturing environment are consistent regardless of whether the control is provided manually or automatically [13]. S88 isolates recipes from equipment. When the software (S88-compliant or otherwise) that defines a product (recipe procedure) and the software to run equipment (phase logic) are in the same device (such as a PLC or DCS), the two different sets of code eventually become indistinguishable and, in some cases, inseparable. This makes recipe and equipment control difficult, if not impossible, to maintain. Every additional ingredient and process improvement can lead to lengthy and error-prone software changes. Documenting and validating such a system is also extremely difficult, and doubly so if not S88-compliant. And however, S88 is important for several reasons but is best known because it has been proven to deliver measurable benefits when properly applied to define and implement batch process automation. Those and many other benefits are the subject of this and following sections. Naturally all benefits come with some cost and the use of S88 is no exception. The primary cost in the case of S88 is the time that needs to be dedicated to learning what the standard teaches and how to use it [14], [15]. In the case of a production manager, the time required to start participating may be no more than an hour or two. Others, who must learn the technology as well as the principles, will spend more time, perhaps a week or more. The time spent is definitely worth the effort, but it is necessary to invest that time in order to derive the benefits that are there for the taking. It can serve as a common language for engineering and operations management to better understand and manage manufacturing automation requirements and benefits. It is an internally consistent standard for automation that reduces the engineering cost for automation. It is a powerful tool for operations managers and engineers with many benefits, but there is a learning curve: short for managers; longer for engineers - a low risk investment with an immediate payback. This can be witnessed from its extensive application in the field. 5. REFERENCES [1] Introduction to S88-For the improvement of the design of batch systems, Japan Batch Forum, jbf.pse143.org/files/s88e.pdf. [2] ISA Organization - ISA88 Batch Standards and User Resources, 2011 the 4th Edition. [3] Joseph Hanlon, Robert Kelsey, Hallie Forcinio Handbook of Package Engineering, 3th edition. [4] ISA Organization - ANSI/ISA Batch Control Part 1: Models and Terminology. [5] Renee Robbins, - New resources for now, 2007, Control Engineering;Dec2006, Vol. 53 Issue 12, p2. [6] James R. Koelsch - International Standards Boost Efficency, Automation World, January [7] ISA Organization - ANSI/ISA Batch Control Part 3: General and site recipe models and representation. [8] W. Covanich, D. McFarlane and A. M. Farid "Guidelines for evaluating the ease of reconfiguration of manufacturing systems", Proc.6th IEEE Int. Conf. Ind. Inf., 2008, pp [9] ISA Organization - ANSI/ISA Batch Control Part 4: Batch Production Records. [10] K. Thramboulidis, S. Sierla, N.Papakonstantinou and K. Koskinen, An IEC Based Approach for Distributed batch Process Control, Proc. of the 5 th IEEE International Conference on Industrial Informatics (INDIN'07), Vienna, Austria, Vol. 1 pp , [11] ISA Organization - ANSI/ISA Batch Control Part 2: Data structures and guidelines for languages. [12] OMAC Packaging Workgroups. [13] Rockwell Automation - Benefits of Manufacturing Control; [14] Pete Lawton - An Examination of the Benefits of a Single Control Platform in Packaging Machinery, ISA Denver Section. [15] Bucur I. Ion, Cupcea Nicolae, Ştefǎnescu Costin, Popescu Cornel, Surpǎţeanu Adrian, Boiangiu Costin-Anton, "Signal Driven Partitioning Large Circuits," The 20-th DAAAM World Symposium, Austria Center Vienna (ACV), 25-28th Nov. 2009, pp