OTS types

An OTS can be categorized in many ways. Here, we will list the three main ways in which to categorize an OTS. The three categories are as follows:

• Representation
• Fidelity
• ICSS representation

Representation

An OTS can be categorized to show how specific it is to the plant that the operators are to be trained on. Under this category, there are two types, namely, generic simulators and replica simulators.

Generic simulators

A generic simulator is defined as a simulator that will simulate a specific type of process, that is, a part of a refinery, a part of an FPSO, a combined cycle power plant, an Ethylene plant, and more. The simulated process is not the same plant as the one the operators are training on. In this type of simulator, the operator's screens will point to equipment that will look and operate in the same way as the ones used by the operator in the plant but will not have the same tag numbers.

Generic simulators are suitable for training new operators on a specific process area or a specific ICSS. They can serve as an introductory level to the processes and controls within a process plant. They are much cheaper and quicker to build in comparison to replica simulators.

Generic simulators are ideal for training and practicing a back-to-basics approach. Underpinning this is an understanding of the principles of process operation and the instruments used. A good example of this is the operation of a cascade instrument loop to control. Cascade control basics are the same, so no matter what you are controlling, you can train the operators on the basics of these loops.

A good example for training companies that offer training courses on generic simulators is ESD Simulation Training (https://www.esd-simulation.com/w/uk). This offers different process and control courses using generic simulators:

Figure 1.8 – ESD training in progress

Another example of such a company is TSC Simulation, https://www.tscsimulation.co.uk/, which is based in the United Kingdom, but there are many others around the world:

Figure 1.9 – TSC's virtual control room

In many cases, a generic simulator will be both beneficial and cost-effective, while in other cases, a more detailed simulation will be needed, as we will discover in the next section.

Replica simulators

A replica simulator is defined as when the simulated process and the ICSS are exactly modeled in the OTS. This allows the operator to see the OTS, including the same graphics, and notice the same behavior between the process and the ICSS.

Replica simulators can be used for specific plant operations, optimization, and can serve as an extended level of testing to process plant design, especially for dynamic and ICSS control checkouts.

An excellent example of a replica simulator is a nuclear plant simulator. Here, the simulator control room is a copy of the actual control room.

Figure 1.10, taken from https://www.wbur.org/earthwhile/2019/05/31/plymouth-reactor-training-center, shows a simulator for Pilgrim Nuclear Power Station:

Figure 1.10 – The Pilgrim Nuclear Power Station simulator

In the following table, we will discuss some of the comparisons between generic simulators and replica simulators:

Table 1.1 – Generic versus replica pros and cons

To sum up, an OTS can be classified by the way it represents the process plant. It can either be a generic simulation model or a replica one. Both have their advantages and disadvantages, which we have tried to highlight in a pros and cons table for ease of comparison. In the next section, we will classify OTS based on the process model of fidelity, which ranges between high-, medium-, and low-fidelity OTS. We will discuss each of them, and we will let you decide which one is more suitable for your business case.

Fidelity

Another way to categorize OTS is by the level of model fidelity, which ranks from low to high and includes a medium step. Describing these different types will help you decide what is good for your specific situation; however, we will discuss this later in the chapter.

Low fidelity

ICSS contractors prefer to call these tie-back simulators, but in reality, they are low fidelity. Some OTS suppliers can only generate a model with ICSS IO points. These can be wired back to the ICSS, making the HMI graphics read default points. As its name suggests, the IOs will tie back to the ICSS and can be varied from the model in a lump way, for example, by turning on or off all the alarms to activate or deactivate them. This can be done in a specific scenario over a specified time. The same thing can be done for analog points to ramp all 4-20 mAmp inputs from 4 to 20 within a specific time ramp.

This will allow you to test that all IO devices are connected properly to the ICSS, and all HMI graphics can be tested using the low-fidelity simulator.

A low-fidelity simulator can be put together in a matter of days or perhaps a couple of weeks, making their cost low.

As low-fidelity simulators are quick to build, they can be used while the replica simulator is being built to train operators for getting familiar with the ICSSes and, in particular, the HMI. I have used this technique in a few of my projects and that proved very useful.

Medium fidelity

When the process model is simplified, for example, by using a water-like component in an oil plant and adding it to the low-fidelity simulator described earlier, we end up with a medium-fidelity simulator.

In this type, the operator's use of the simulators is slightly improved, creating a familiarization system for them. Operators can open and close valves and start and stop motors with a very low level of dynamic response fidelity.

On the other hand, ICSS use is dramatically increased in comparison to the low-fidelity model. These types of simulators can be used to validate controls, safety, and alarm philosophies. In such simulators, automatic sequences can be checked out, as these are never adequately tested in an ICSS FAT.

The time required to build these is typically 2–3 months (of course, this depends on how big the process model is and the use of automatic tools to generate the model, for example, reading smart P&IDs). This will make the price for these simulators higher than the low-fidelity ones.

High fidelity

This type of model is built based on actual P&IDs, datasheets, Heat and Mass (H&M) balance reports, and all other process inputs.

All process dynamics, pipe volumes, valve CVs and characteristics, and pump and compressor curves are used to build the model. In turn, this model is integrated into the ICSS, making the simulator behave as close as possible to the real plant.

This will dramatically increase the use of the simulator for operator training, dynamic studies, and plant optimization.

These simulators will take anything between 12 and 24 months to build, making their cost the highest of all.

Figure 1.12 describes the effectiveness of all three types of simulators versus the cost and time taken to build the simulator.

In the lower-left corner, we see the low-fidelity simulators showing a low cost and being quick to build, with little use. In the middle, we see that the medium-fidelity simulators show a little use on the operator training side but more use on the ICSS side, taking the price and time to build slightly higher.

In the upper-right corner, we see high fidelity reflecting the model use of the simulators, but at the same time, at a much higher cost and with a much longer time to build.

A good scope document should list all the uses of the simulator against cost and justify the investment, as we will see in later chapters of this book:

Figure 1.11 – OTS effectiveness versus cost

In this section, we have learned how an OTS can be a low-, medium-, or high-fidelity simulation process. Each will have its own uses and advantages. Before making the OTS investment, it is always advisable to get all the project stakeholders to agree on which OTS type will bring the most benefits to the business.

In the next section, we will classify an OTS based on its ICSS representation.

ICSS representation

Another way of categorizing OTS is by the way the ICSS is simulated.

Emulated

This was a well-known solution in the 1980s and early 1990s. ICSS contractors did not have well-developed connections when it came to modeling software. Some OTS companies, or OTS teams diverted from process control suppling companies, introduced this solution to the market.

In this solution, all HMI graphics of the ICSS are redrawn, and the ICSS logic is converted into a model that can run on a personal computer. Sometimes, this process is done automatically, while at other times, the process is manual or semi-automatic.

Of course, this was very costly, and errors were likely to be made in the conversion, which would have meant longer integration, OTS commissioning, and approval processes. In those days, that gave simulators a very bad reputation.

As the ICSS suppliers started to make links to the process models possible, this solution started disappearing from the market; however, in recent years, it started making a comeback due to the market pushing for lower-price OTS models and OTS supplier competition increasing. But today, these simulators should no longer be on the market, as we have a proper solution, and using these will make the simulator much less useful. Additionally, the bitterness in the market toward OTS makes the idea not worth it!

Stimulated

In this type of OTS, the actual ICSS controllers are used in the simulator along with the same ICSS hardware. Therefore, the HMI operator station is the same as the one used in the control room for the plant that is being simulated.

This technique is no longer used as it is very expensive, but it will give the same reaction as the actual ICSS. This is because the hardware is the same.

Hybrid

Many ICSS suppliers have created a solution in which to run an emulation of their controllers on a computer that can be integrated with an OTS. The control is faithfully emulated, and the code is exactly the same as the one that runs in the ICSS controller. Additionally, the HMI is exactly the same as the one used in the control room.

Usually, this type is referred to as "emulated" OTS; however, in this book, we will use "hybrid" as the emulation here is different from the emulated type of simulator. The emulation here is done by the ICSS contractor, and the control's code is the same as the one used in the ICSS controller.

This solution has been adopted by many ICSS suppliers, such as Yokogawa, Honeywell, Schneider, and Emerson, just to mention some of the major players in control automation within the process industry:

Figure 1.12 – OTS types

So far, we have classified OTS as both generic and a replica, based on its plant representation. Following this, we classified OTS based on its model representation, including low-, medium-, and high-fidelity simulation models.

Finally, we classified OTS based on its ICSS representation, and we discussed emulated, stimulated, and hybrid systems.

In the next section, we will discuss how third-party controls are represented in an OTS.