Considerations for the Design of an ISA-S88 Equipment Model: Part B
A preferred approach to the design of an equipment model is based upon a sequence of seven steps.
- Determine the boundaries of the process.
- Determine the units and containers that are involved.
- Follow the flow of materials.
- What is done to the materials in a unit?
- Identify unit tags.
- Determine equipment arbitration.
- Determine the Parameter and Report values.
The paper provides details of these seven steps and how they can be used in the development of an ISA-S88 equipment model.
- The boundaries of the process:
The upstream boundary covers incoming materials whereas the downstream boundary refers to all finished product storage activities, usually storage of the products of the process. The vertical boundary indicates integration with the ERP to receive orders and to report materials produced and consumed. The fourth boundary covers reports to be generated, particularly any reports that are specifically requested by customers as well as the programming standards to be used.
- Determination of units and containers:
This is a very important activity. The FactoryTalkBatch program is priced per unit. Consequently, poor definition of the number of units in the model can result in high costs rendering the project not viable.
Containers are typically tanks, drums and pallets, supper sacks, etc. i.e., the pieces of equipment in which materials are stored.
The traditional definition of a unit is a piece of equipment which combines and/or transforms ingredients to add value to an interim product or to the final product. We believe that this can be misinterpreted and therefore recommend thinking about the Unit the following way:
“any location, whether equipment related, or non-equipment related in which a sequence or procedure is performed”
Based on this definition, an empty room or area in which manual pre-weighing of materials is conducted is a unit, even though no automated equipment is involved or required. Clean-in-Place equipment that requires a sequence or recipe to make up the cleaning solutions will also be defined as a unity. This approach extends to those parts of the CIP equipment that requires cleaning independently of a tank or vessel, e.g. sections of a transfer line through which materials move between tanks.
What is NOT a unit? Typically heat exchangers are not units unless an independent procedure is performed in it. An example is the heat exchanger that is used only to control the temperature of the water and is not counted as a unit.
The Equipment Editor (a component of FactoryTalkBatch) is used in the development of the equipment model and is an excellent place to document units and containers.
- Follow the flow of materials:
This step requires the identification of the phases that (a) bring materials into the process system, (b) move materials within the system, and (c) transfer materials (usually the products) out of the system and into storage. A straightforward approach is to begin at the top and center of the units in P&ID and follow the perimeter of the diagram identifying what actions are taken at each piece of equipment interacting with the unit. For example, the action of adding water, oil; transferring material to another tank; unloading the tank.
- What is done to the materials:
This is effectively a continuation of the previous step, following the P&ID to identify the actions that occur. For example, an action may be to agitate the mixture or possibly to heat/cool to a specific temperature. Some phases could be used to control pressure or to prompt an operator to perform manual tasks, such as submit a sample to the laboratory or prompt closure of a lid of a vessel.
It should be noted that not all phases to be identified in the equipment model are reflected in the P&ID, these will indicate what the equipment can do. The model will include tasks that are performed by operators, these tasks also being defined as phases.
- Identify unit tags:
Unit Tags can be values of weight, temperature, level, or pH in some cases, that are displayed at each unit in the equipment model and are available to the recipe author to allow decisions to be made in the recipe based on process conditions. Example: “start adding a second material after the tank has reached a desired weight” or “add material after the temperature drops below or exceeds a target temperature.”
The Equipment Editor can again be used to document the phases for each unit.
- Determine equipment arbitration.
Example: the need for arbitration applied only to recirculation at tanks 301 and 302. The actions will occur one at a time using the shared resource. If the units were programmed in different controllers it will be necessary to create two phases, one for 301 and one for 302, and to provide a recirculation loop as a resource to allow arbitration.
- Parameters and Reports:
This is where the bulk of the project work is defined. Keep in mind that the engineers building the project may not be the user creating recipes nor operating the batch system. It is important, therefore, to use meaningful names for parameter and report names, be consistent with the naming conventions. For example, the representation of a parameter might be:
and the corresponding report should be
Set points for given parameters may be changed by an operator and it is very important that ALL changes be documented in the phase reports.
It is convenient to use parameters to prompt operators. If equipment has faulted or is in manual mode, then the action cannot be completed. To counteract this a phase parameter can be created to prompt the operator to check the equipment. This is shown as
The OO indicating “operator origin,” specifying how the phase is to be configured. Note that since the recipe author does not need to know how equipment is configured a parameter should relate to the basic function at hand and allow the logic to adapt for differences in the equipment.
Parameters originate at all levels. The control module may have a parameter that addresses the question “how long should a valve take to open before it is considered faulty?” On the procedural side, parameters may originate at all levels, i.e. the procedure, unit procedure, operation, and recipe phase. Most of the parameters will be at the recipe phase and equipment phase levels. On the procedural side, some parameters at the recipe phase level may be deferred to the procedural level to create an interface with the ERP. Similarly, parameters at the equipment phase may be deferred to lower levels. “Not all parameters required to perform a task need be in the recipe.”
Batching activities are recorded in the event journal. Report values need to be useful in determining the product quality as well as providing an understanding of what occurred during the execution of the recipe.
Considerations For The Design Of An Equipment Model
- How does the phase interact with operators and automation control system?
- What information is recorded and made available to an operator and journals?
- How does a phase respond to failure of a component in the equipment?
The second paper will present seven steps that are recommended to be followed in the design of the Equipment Model.
In considering the design of the phases it may be useful, as an illustration, to equate a phase to an ideal operator, who approaches a unit, selects a module of interest, e.g. water addition, or temperature control, and using the HMI pop-up inserts the values required for the process. Those actions are some of the function of the phase. In addition, it is important that before any actions are taken, the phase should establish the status of the equipment to be used and inform the operator of conditions of exceptions. Any abnormal conditions will be logged, and the operator can obtain specific information about the equipment. Is any component faulted? What and where is the fault? Are any components in manual mode?
Phases should NOT automatically change the mode of their subordinate equipment but rather should prompt an operator if such changes are desired. For example, if it is logged that a component of the equipment is in manual mode the phase should only inform the operator of this condition and not change it to auto in order to run the equipment. All changes in parameter set points, changes that may be carried out by an operator or code, must be logged by the phase. If for any reason phase failure occurs (typically an equipment failure), the phase should be commanded to go into HOLD and specific information regarding the cause of the failure should be logged. It is preferable that to complete a task a phase does not depend upon a parallel phase be required unless required by the functionality. In such instances, the recipe author must know the logic involved, a situation that is not desirable. Furthermore, the absence of such dependence can simplify the design.
It should be understood there are situations where the coordination of phases is necessary. An example is the Transfer IN and Transfer OUT activities that occur between units. In a material addition activity, the phase should identify if a dosing error occurred, informing the operator of the error showing it as “out of tolerance high” or “out of tolerance low” and allow to adjust to that condition. Another situation that requires the coordination of phases is the use of multiple phases requiring common resources. For example, providing water addition to multiple locations when totalized with a common flow meter, this will require arbitration, i.e. the coordination control that becomes necessary to determine how a resource should be allocated when the demands for that resource are many at one time. The use of a common phase can minimize arbitration. It is preferred that one phase be shared by multiple units. However, it may be necessary to use multiple phases where different units and their phases are controlled by different controllers (PLCs). In such cases, a resource is created that is arbitrated among the multiple phases.
In the design of the Equipment-model advantage should be taken of the availability of Material Manager, a component of FactoryTalkBatch. The Material Manager has the capability
- to identify the location of the resources, i.e. are they stored in tanks, silos, supersacks, barrels, drums, or on pallets,
- to define and control the type of material allowed in each location e.g. rice rather than corn, fine grain material not coarse material,
- to prioritize the usage of the materials when found in various storage locations,
- to define material properties such as density, moisture content, concentration, potency, humidity, pH, etc. This allows the phase to compensate for variations in material properties, such as moisture content, potency, etc.
It is strongly recommended that individual documents are developed for each phase or Phase class in which all relevant design information is captured. i.e. phase logic, Phase failures that may occur, interactions with operators and the equipment model design. The creation of documents for each phase reduces the time spent waiting for all documents to be completed before programming activities can be initiated. Some phases such as agitation, or prompting the operator, are well established so that programming of those phases can be undertaken before all documents are complete. This allows an earlier completion of the project as well as staggering of tasks. The terms used in naming Parameter and Reports (Tags) must be meaningful and not rather obscure engineering terms that make little or no sense to the recipe authors or the audience of this data.
Phases can take advantage of the availability of high order functions on today’s controllers, mathematical derivatives and integrals, or possibly the use of fuzzy logic or advanced process control. This capability may allow the determination of the efficiency of a single phase, which may be designated as the phase OEE. Information is collected for individual phases and these calculations to calculate a flow rate in the absence of a flowmeter e.g., the change in weight of a tank with time during the addition of material, defines the flow rate which in turn allows prediction of the total time that will be required to complete the dosing activity. Integration of temperature-time profiles during a heating process will indicate the amount of heat impinged on the product. This can give an indication of the amount of cooking as well as the sterilization of the equipment during the CIP & SIP tasks. Integrals also allow the determination of the total power used in agitation activity. Generic timer phases can be used to determine recipe activities OEE, by placing count-up timers in parallel with the recipe activities, allows us to utilize this data and information to determine the OEE of each activity of the recipe and not just the overall time it took to complete a recipe
With all the above requirements in mind, we can proceed to considering the topic of the second paper – The Seven Steps to the design of an Equipment Model.
Introducing A New Line? What’s Your Breakdown Plan?
The marked increase in the use of automation in manufacturing industries has been driven not only by the need to realize the lowest possible costs for a product but also by consumer demand for variety and customization. Control systems are cost-effective and provide the means to maximize efficiency and accuracy of the processing lines. Therefore, today the set-up, change-over, product scheduling, and sequencing, together with quality control are necessarily automated. The control systems also allow the collation of documentation for all materials and processes used in production, which is essential to meet product safety. It is also necessary to be able to recall defective products quickly and cost-effectively. These demands have led to the integration of critical information from the plant floor and from suppliers into corporate enterprise resource planning systems.
The adoption of automation technology has not happened without problems. In the planning stages for the installation of control systems, the focus is predominately upon the existing product line or new process and the in-house production team that will be involved. Training programs to improve the skills of the in-house production team and/or the hiring of additional engineers with the required skills will be included in the planning stages. The plant services are often overlooked, yet it is these engineers, technicians, and electricians that will be required to respond to maintenance problems that arise, some of which may result in costly downtime. It is possible that there is a lack of understanding of automation technology within management. It has been suggested that in some instances the control systems selected for a project may be limited to the ability of the available in-house engineers and electricians (the KISS philosophy). This apparent reluctance to accept automation is somewhat reminiscent of the reaction to the introduction of fuel injectors in automobile engines several decades ago. The fuel injector represented an innovative technology that at first was regarded as complicated and it replaced the carburetor, which was a simple engine part. Technology for the automobile has advanced to such a degree that today it requires the assistance of a computer (a specialized technician) to service the engine. Yet this is no longer difficult to accept. Similarly, it should be realized that the maintenance of control systems and automated equipment will require “a computer,” that is expertise not readily found in the electricians and engineers that make up the in-house plant services.
Automation brings the ability to control, process, track and manage production in real time while reducing labor costs and improving efficiency. However, once a company has invested in automation technology, that technology and equipment must be protected from breakdown and the expected early wear and tear. As stated earlier, the question of how to provide that protection, particularly over the long term, is not often addressed in the planning stages. It may be that providing the required support services increases the overall project costs and this is a concern to management. But surely it is obvious that such support will be needed.
There are three approaches to the maintenance of control systems and automation equipment that may be considered:
- Create an in-house team of electricians, engineers, and technicians to provide the necessary maintenance and support. This will likely require the addition of personnel with specific skills related to automation. Training programs directed to support services may be introduced, the training customized to the product line.
- Completely outsource maintenance activities related to the control systems and automation equipment.
- Establish a hybrid arrangement in which the mission-critical engineering skills are kept in-house, but general maintenance services are outsourced.
There is a key factor that should be considered in determining how to best provide maintenance and support services. Determination of the impact of downtime should be given the highest priority since downtime affects both productivity and profitability. Establishing in-house capability that can quickly deal with breakdown problems is advantageous. However, it must be recognized that the in-house team will need ALL the necessary skills related to automation technology and control systems to quickly deal with every problem over the long term.
If it is decided to keep the critical engineering skills in-house several questions arise:
- What is the availability of skilled engineers and electricians?
- With possibly a relatively small number of skilled individuals available, do you hire to support current operating systems or for new processes under consideration?
- Should you seek multi-skilled individuals with considerable experience in automation?
- Should these individuals have the ability to grow and change as technology changes and how is this ability recognized?
- Are you able to offer attractive compensation packages, including pension and healthcare benefits as well as salary?
- Will you be able to retain these individuals?
- Is the location of the plant attractive and interesting to mobile, skilled engineers?
Clearly, these questions only apply to options 1 and 3. Completely outsourcing maintenance activities avoids these uncertainties, and it is possible to acquire the skills needed without long-term commitments to employees. However, it is recognized in manufacturing industries that plant managers may struggle with the loss of control that results from outsourcing activities. Under these circumstances, the plant manager finds it difficult to directly manage, set priorities, and instruct the workforce. Yet, without question outsourcing delivers expertise, efficiently provides high-quality work and is NOT costlier than establishing in-house capabilities.
Finally, it is the responsibility of the end user to determine the focus, flexibility, control, and cost-effectiveness, required to manage maintenance activities. Automation has perhaps upset the traditional balance between the process and the maintenance required by that process. Automation and today’s control systems demand a range of specific skills to install and maintain and outsourcing does offer immediate access to those skills. It may be argued that many companies are prepared to invest in their own people, recognizing the positive impact that competent and responsive maintenance has on their business. That indeed may well be true but there are situations where it is better to outsource the responsibility, e.g., the lack of sufficient skilled people being available, where maintenance is cyclical and has periods of low activity, where equipment is highly specialized or where the facility is too small to warrant investment in an in-house maintenance function.
Dynamic Formulation Improves Quality
The science of formulating products requires an understanding of how material properties can affect the final product. Making changes to recipe set-points to accommodate for varying process conditions and material properties is commonly performed in the industry. The team or individual responsible for calculating the required amounts of material will be referred to as the ‘Formulator’. Often this aspect of the science can be described as a set of equations used by the Formulator to adjust the amount of material required. The following is a simple example to illustrate a common process to adjust the formula of a product. A Formulator has a Site-Recipe that requires a blend of:
The properties of each lot of material may come from the material supplier or may be derived by the end-user’s lab analysis. The material to be used in this example is moist (Material_Moist) and contains 20% moisture (Moisture_%).
Since the material is moist, the Formulator calculates the amount of moist material (Material_Moist) required and adjust the Water (H2O) required to obtain the desired ratios and specifies it on the Master Recipe.
Therefore, the Control-Recipe should call for 120 kg of moist Material to obtain the 100 kg of dry Material needed. Water introduced by the moist material (Material_H2O) is then factored into the amount required for a batch.
This scenario describes what is very common in the batching industry. The Formulator is required to modify the Master recipe to accommodate for changing raw material properties. There are many more factors that can be taken into consideration when adjusting the amount of material such as concentration, potency, percent fat, percent solids, sweetness, etc.
The automation solution can be constructed to allow the recipe author to specify the properties to be dosed (100 kg Dry material & 100 kg H2O) and allow the control system to perform these calculations by tying a material management system to the batching system. Dynamically adjusting the amount of material required becomes a very practical solution since the master recipe doesn’t have to be modified to adapt for changing raw material properties.
The experienced team at ECS Solutions takes a simple approach using an ISA-88 based standard commercially available off the shelf Software. A phase is created that provides the Formulator the ability to specify the amount of Dry Material to be added or the Amount of Moist material required. If the Amount of Dry Material is specified, then the control system will determine the amount of moist material required.
If a container runs out of material during the addition, and it is considered an incomplete feed, the Software will find another container with the required material, it will request the properties of that new lot ID, and complete the addition considering those new properties. The amounts, and lot IDs of materials used are automatically reported in the Batch journal. In addition to creating a master recipe that doesn’t have to be modified to accommodate for changing material properties, dynamic formulation is especially practical to accommodate for unplanned activities such as having to switch to a different material source. Dynamic Formulation eliminates the risk of having to perform manual calculations and recipe updates at the correct time, while allowing the Quality of the products to be improved.