📑Process Data

Processes are designed to change the chemical or physical properties of upstream materials to more useful downstream products. These changes must be monitored and controlled during this transition. Accurate and timely measurements on the physical and chemical properties of the process are crucial to controlling the process, as well as the outcome. These measurements referred to as process data.

Numerous field devices are used to generate process data. Flow, level, temperature, and pressure are common sources of process data; however, many other parameters of complex processes must also be measured. For example, a water treatment plant relies on accurate pH and turbidity measurements in addition to flow, level, and pressure to produce clean water. An ICS uses these measurements for adjusting control devices to ensure the product (in this example, treated water) meets specifications.

Process data are not only used for control. For example, the data can also be used to:

• Meet regulatory requirements

• Track energy costs

• Provide design inputs for the process enhancements (i.e., identify and justify capital improvements)

• Control inventory\determine product pricing.

Data Flows

The data flow through ICS varies by vendor, topology, and protocols. The network can be wired or wireless, but it links the components of the ICS. The HMI receives information from the field controllers, relaying information through communication protocols and providing the operator with a view of what is happening in the process.

This diagram is a simplified representation of an ICS communication network. The process is controlled by an application running inside the field controllers, which communicates with a series of field inputs and outputs devices. The field controllers consolidate the data and transmits it to the HMI stations where it is presented on displays.

Control Loops

A typical ICS contains numerous control loops, human interfaces, as well as remote diagnostics and maintenance tools. They are built using an array of network protocols on layered network architectures, allowing ICS support staff and vendors access to diagnose and correct operational problems.

A control loop, single-loop control is the fundamental building block of industrial control systems. It is communication used to regulate the process. It consists of a group of components working together as a system to achieve and maintain a desired value of a system variable by manipulating the value of another variable in the control loop.

For example, a field device sensor produces a measurement of a physical property and sends this information as controlled variables to the controller. The controller interprets the signals and generates corresponding manipulated variables, based on set points, which it transmits to the actuators (field devices), such as control valves, breakers, switches, and motors. These field devices are used to directly manipulate the controlled process based on commands from the controller. Control can be fully automated or include a human in the loop.

Sometimes these control loops are nested and/or cascading – whereby when multiple sensors are available from measuring conditions in a controlled process, a cascade control system can often perform better than a traditional single-loop. For example, the steam-supplied water heater shown heats water using cascade control. The second controller has taken over responsibility of manipulating the valve opening based on measurements from a second sensor monitoring the steam flow rate.

Process Flows

This graphic depicts the ICS process flow. We see the field devices that provide the process data. This is where the actual physical process happens, be it the mixing of chemicals or the management of trains, or the measuring of the pressure of gas at a certain point in a pipeline.

A field controller collects information from field devices and assesses, manages, and processes state information about the process.

The HMI monitors the information and presents it to an operator. The operator uses the HMI to observe the process, watch for events and alarms, and to make decisions or adjust the system to keep the process stable and safe, as required. The operator function can be performed by a person, or a system such as an EMS, DCS, or any a specialized system that may be unique to a particular sector.