Process monitoring and
control systems

What they do and how it helps

At the heart of this least-sum-of-all-costs approach is a well-designed process and equipment monitoring and control system. In turn, this must be integrated seamlessly with higher level systems, such as the CMMS, MRP or ERP, and other manufacturing systems.

Process and equipment monitoring and control devices have been with us for a long time, beginning with completely mechanical programmable logic controllers (PLC's), moving to electro-mechanical relays and timers, and since the early 70s, electronic programmable controllers (PC's). However, the information systems component of these systems only recently gained importance through introduction of sophisticated computer graphics, mass storage devices, and integration capability with higher level applications.

What is it?
The term process and equipment monitoring and control can be defined as follows:

Process--a series of actions, events, or conditions to achieve a given end result. For example, mixing four ingredients, applying heat and filling containers with the resultant product is a process.

Equipment--the machines or apparatus required for the process. Examples from the above process might be blenders, cookers, and fillers.

Monitor--collecting data as to the status of the labour, material, or overhead components of the process or equipment. Examples for the above might be kilograms of finished product per man-hour, downtime, and temperature range on cook cycle.

Control--regulation of a process or equipment using a feedback loop and based on the monitoring of the process or equipment. Again, examples for the above could be automatic adjustment of temperature of a cook cycle to maintain within acceptable range, automatic shut-off when a container is filled to correct weight, and beginning the next cycle to avoid downtime.

One reason is to allow human operators to override the computer for specials or experimentation. Another reason is to avoid total system failure if the computer should malfunction.

Process and equipment monitoring and control systems range from simple temperature monitoring systems to sophisticated computer-aided manufacturing systems in a lights-out factory environment. These systems are used for on-line, real-time monitoring and control of process measures such as temperature, pressure, flow rate and humidity; equipment measures including impedance, position, wear and downtime; material measures, for example, inventory, throughput, yield, and scrap; and labour measures such as utilization and performance.

Configuring a system
Process and equipment monitoring and control systems have the following components:

Input devices--There are three possible types of input devices. They are measurement devices such as a pressure gauges, detection devices such as a photocells, and recognition devices such as a barcode scanners.

Processors--A variety of processors are available to collect and manage the data input from the shop floor. This includes programmable controllers, micro to mainframe computers, and proprietary processors that come direct from the equipment manufacturer.

Output devices--There are three possible types of output devices that present the interpreted shop-floor data in a manner in which humans or machines can take appropriate action. The three types are monitoring devices such as a graphic displays, control devices such as a reset switches, and storage devices such as a laser disks.

Communications network--To link the various components described above, you need some sort of communications network. As well, the process and equipment monitoring and control system must be integrated to higher level systems such as the CMMS for input into predictive maintenance, preventive maintenance, labour reporting, inventory management and other applications.

Controls, equipment, and process monitoring
Even a full-blown computerized control system requires a back-up monitoring system. One reason is to allow human operators to override the computer for specials or experimentation. Another reason is to avoid total system failure if the computer should malfunction. As well, good records can provide cost-justification for new equipment--for example, downtime recording--a manual check on computer-controlled operations, experimental data for improving a process or new product development, and an audit trail for security and maintenance purposes.

There are three approaches to the monitoring component of process and equipment monitoring and control. Some systems are configured so that a standard computer can run custom or proprietary software interfaces with the process controller. Other systems use third-party hardware and software such as a CMMS for data management. Finally, data management capability can be built directly into the process controller.

When comparing data management system options, choose hardware and software that is easy to learn and use, easy to change, easily expanded both in size and functionality, and capable of integration with many types and makes of programmable controllers and input/output devices. You should also be able to access and even manipulate the data from any other operator workstation in the plant regardless of which processes or equipment are being controlled by the local hardware and software. This can be accomplished through use of a good communications network that provides the link.

Process and equipment monitoring systems can present both on-line, real-time data, or historical data in either on-screen or hard-copy formats. There are various formats used by vendors to display the data. These include high resolution graphics, alarm summaries in spreadsheet format, trend graphs, and standard reports.

You can purchase a low-end, turnkey starter system for about $20,000 to $50,000 depending on the number and type of input and output points you require. Another variable is the data management requirements.

Key savings and benefits
Process and equipment monitoring and control systems are not inexpensive. You can purchase a low-end, turnkey starter system for about $20,000 to $50,000 depending on the number and type of input and output points you require. Another variable is the data management requirements. For example, that could be the number of screens required, how much and how often data will be collected, reporting features selected--graphics, alarming, data storage, or custom programming. Prices escalate quickly to $500,000 and beyond for larger systems with more than 4,000 input/output points.

Because the systems are expensive, many companies find cost-justification difficult. Another problem relevant to monitoring systems as opposed to automatic control systems is that if you do not act on the information you collect, the savings opportunity are lost. Nonetheless, companies that have made the move to process and equipment monitoring and control systems have claimed substantial savings and benefits as summarized below.

Greater consistency--This is the single, most important benefit cited by the vast majority of companies. For example, with older systems, if you asked the temperature of the material in a vessel, the operator would look at a gauge and estimate. With a modern system, that same operator can answer you to within two decimals. Thus actions are taken on a consistent basis, and therefore the finished product is more consistent.

Material savings--By improving accuracy and timeliness of data collection, savings are generated through improved product quality, reduced inventories, improved yield, and reduced scrap, refeed, rework and product losses. For example, monitoring and controlling the amount of material entering a process, the length of time material is subjected to equipment cycling, and the critical temperature of a process impact the quality and yield of a batch.

Reduced downtime--Replacing antiquated equipment with modern technology leads to ease-of-troubleshooting, increased reliability of equipment, ease-of-system-expansion and change, and ease-of-use for operators. These factors, in turn, reduce downtime dramatically.

Reduced human error--Judgment errors can be expensive and dangerous. For example, if something critical fails because of, say, an overpressured vessel or improper placement by a robot material handler, an automatic control system avoids human reaction time. This saves lives and product. As well, good data management systems facilitate root cause analysis.

Reduced set-ups and changeovers--Continuous processing means increased uptime of equipment, and, therefore, increased product throughput. It also results in improved labour utilization.

Greater flexibility--Older systems occupy valuable space and are difficult to service or change. Modern systems are flexible. Examples of procedures that are simplified are adding or eliminating input and output points, changing the control logic, accessing information using colour graphics and other data management features, tailoring the information to the changing needs of operators and management, servicing the equipment, and communicating with parallel systems and higher level programs like a CMMS.

With older systems, operators are required to monitor and control the process and equipment at stations spread throughout the plant.

Labour savings--By centralizing and simplifying the monitoring and control functions, operators can be eliminated. With older systems, operators are required to monitor and control the process and equipment at stations spread throughout the plant. As a result, operator utilization is low. The control aspect can be automated and stations can be combined through centralized monitoring. Human operators are still required in case of system failure.

A few large companies have totally centralized control rooms from which every aspect of operations are monitored and controlled. Only maintenance personnel are required in the plant itself.