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Process control systems make sure industrial processes are carried out efficiently, consistently and with as little variation as possible. They're installed in industrial settings to:

• help maintain throughput, quality, yield and energy efficiency
• make sure working practices are carried out safely and profitably

Systems measure, monitor and control manufacturing processes and activities. They identify and correct any abnormalities or variations from specified values, either manually or automatically. The aim is to make sure that production is consistent and that as little energy is wasted as possible.

Although process control technology has advanced rapidly since the mid 1980s, the latest systems still follow the traditional hierarchical or pyramid-like structure. The lowest level of the pyramid works to make sure a particular process doesn't vary by more than an allowed amount. It monitors the operation of each part of the process, identifies unwanted changes and initiates any necessary corrective actions.

Lower-level controls can't handle complex situations like equipment faults. These have to be dealt with either manually, by an operator, or by other controls at a higher level of the hierarchy.

Further up the pyramid the system controls the overall production process and makes sure it continues to operate efficiently.

Benefits of an efficient process control system

Your business could benefit from a well-designed control system in many ways, including:

• energy savings - energy wastage is reduced when your plant and machinery are efficiently operated
• improved safety - control systems automatically warn you of any abnormalities which minimises the risk of accidents
• consistent product quality - variations in product quality are kept to a minimum and reduce your wastage
• lower manufacturing costs - detecting faults early means throughput, yield and quality are maintained
• improved environmental performance - systems can give you an early warning of a rise in emissions

Your business could achieve energy savings of up to 15 per cent with a well-designed and properly maintained process control system.

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Process control systems monitor industrial processes to make sure they don't vary from pre-set limits. They start corrective action if they find unwanted deviations or abnormalities.

Basic closed-loop control

The key element of a process control system is the basic closed-loop control. Systems usually include many hundreds of individual control loops, each of which controls one aspect of a particular process - for example, the temperature of an oven. The control loop's job is to make sure that a particular variable or parameter is maintained at its pre-set value, or 'set-point', and doesn't vary from this by more than an acceptable amount.

The control loop must also react quickly to any changes in set-point so that production isn't interrupted.

To achieve this, a control loop is made up of three main components - the measurement device, the controller and the regulator.

Measurement device

To stop any unwanted variation in a production process, a control loop monitors the process regularly to check it's performing as it should. This is usually done by a sensor that measures a particular property like temperature. A transmitter converts the sensor's output into a signal which is sent to a controller. The signal can be sent individually or with other signals through a special network - called a 'fieldbus'.

The controller

The controller compares the measurement recorded by the sensor against the pre-set value. If there's an unacceptable difference it initiates appropriate action. For example, if an oven's temperature has fallen too far, it instructs the regulator to send more fuel to the burners to increase it up to the required set-point.

Most of the control tasks required by an industrial process can be handled by a well-designed and well-tuned single-loop controller. These normally monitor a single measurement and adjust one regulator, but they can also be linked to another controller to adjust another related set-point. This is known as a 'cascade system'.

The regulator

The regulator controls the throughput of the process. It responds to commands from the controller and makes adjustments where necessary. Control valves are the most common type of regulator - these adjust the flow of a fluid in response to messages from the controller. A variable speed pump is an alternative type of regulator that controls the flow of a fluid more accurately and with greater energy efficiency. Variable speed drives can also be used where the controller regulates the movement of solid materials rather than fluids or gases.

If your process control system is more than 20 years old it's worth considering upgrading it. Installing new digital technology can reduce your staffing levels and maintenance costs and improve the efficiency of your production operations. As well as basic closed-loop controls, there are modern systems capable of more complex control.

Sequence controllers

You can replace single-loop controllers that are used to sequence simple activities, like the mechanical operations involved in process start up and shut down, with sequence controllers such as programmable logic controllers. These can be expanded as different aspects of production are automated. They can include both single-loop and more advanced controllers.

Distributed control systems

These are modular systems that control large or complex processes. Operators can adjust the set-points of many different controllers from a central control room. A high-speed network or 'control bus' connects each controller to a central control unit. This sends messages such as fault codes to other high-level systems so that you can make sure you achieve high levels of quality and throughput.

Supervisory control and data-acquisition systems

These sophisticated software packages are used to control a wide range of industrial processes and can store production details so that they can be analysed later. Advanced systems include features that help operators to control and optimise production automatically.

Issues to consider before upgrading

If you decide to upgrade your process control system, you should plan carefully as it will involve a high capital cost. You can do this by:

• keeping it simple - ensuring your proposed system isn't unnecessarily complicated and expensive
• carrying out a feasibility study - estimating what the project will cost and the value of the benefits it will bring
• involving team members - making sure everyone who will be managing, operating and maintaining the system is part of the planning
• carrying out a pilot study on part of the process control system
• raising staff awareness about the new system and why it's been installed
• putting operator training in place
• setting up a maintenance schedule to keep the system running efficiently

The performance of your process control system may gradually decline over time because your operators override the system, or your equipment and plant develop faults. You may not be aware that the system is performing badly because maintenance schedules don't always include the right checks to identify problems. If your system is poorly-maintained, your processes won't be operating efficiently and your energy costs will be higher than necessary.

Indications that your system isn't performing well may include:

• operators setting controllers to manual when they should be on automatic mode
• inefficient operation
• too much variability
• frequent calls for repairs and maintenance

The maintenance approach itself may be the cause of many problems. If 'quick fix' breakdown maintenance is carried out in response to equipment failure, underlying problems may never be sorted out and can become permanent. A planned preventive maintenance strategy involves carrying out maintenance tasks regardless of whether a machine has broken down. This can also help you identify opportunities to enhance or upgrade your system.

Produce a maintenance manual and use a log book

If you have a good maintenance manual, you will be able to keep process control systems working well and make sure that you don't overlook routine maintenance tasks. You should include in the manual:

• details of all maintenance tasks, who is responsible for them, and how often they must be done
• schematic diagrams of all equipment and controls
• operating instructions including emergency shutdown procedures
• contact details for equipment manufacturers, and installation and maintenance technicians

You should always make sure the key parts of the system are working correctly. Carry out regular checks on:

• instruments - get faulty instruments repaired or recalibrated by qualified personnel
• measurement devices - correct problems caused by poor installation of sensors
• valves - check for 'sticky' valves which increase energy consumption

You should also keep detailed records of all your maintenance activity in a log book. This will help you when:

• dealing with problems that keep happening
• improving process control - for example by training operatives or replacing manual controls with automatic ones
• upgrading your equipment if it has reached the end of its useful life

Although process control systems only use a small percentage of the total amount of energy consumed in a typical industrial unit, they directly affect how efficiently all the plant and machinery on the site works. So making sure your process control system is well tuned and working correctly is very cost-effective and can lead to substantial energy savings.

The performance of a control system declines over time as the system becomes de-tuned. Tuning it regularly means that it continues to work as well and efficiently as possible. Tuning - or 'optimising' - a process control loop involves adjusting the controller so that it responds more quickly to changes in the process. Tuning requires no capital investment and it is easy to measure the cost-savings from doing so quickly.

Automatic control

One of the signs that a control system has become de-tuned is when operators frequently override automatic controls and switch to manual operation, which is much less efficient. You should check at key times - such as shift changes - that operators haven't set systems to manual operation unnecessarily.

Staff training

Making sure your staff are trained to recognise and deal with tuning problems in control systems themselves can reduce the number of calls for maintenance and get processes back to normal quickly.

Monitoring

You should monitor your production processes regularly to help you identify where systems have become inefficient. You should look out for signs that your controls need tuning. These include:

• Excessive or variable energy use. Check that the specific energy consumption per unit of product is consistent. If you measure the energy used per unit of product at different times, but when throughput is the same, this will help determine whether energy use is consistent.
• Over-purification or over-specification of the product. This can occur when the system is using incorrect settings so that it over-reacts to small changes.
• Control disturbances. These can happen if your system isn't set up to compensate automatically for external changes - such as a drop in pressure - before it sets off plant alarms or safety trips.
• Time delays and dead time. Fine tuning the controller can help to avoid dead time caused by the slow response of the system to changes.

As well as highlighting where systems need attention, monitoring also helps you to establish where you could put in place energy-saving measures in the future.

Following the steps below will help you improve the way your process control system operates and reduce your energy costs.

1. Investigate the current system

Monitor your system's performance and walk around your site looking for signs of poor control. These include inconsistencies in product quality, variations in the energy used per unit of product, controls set to manual instead of automatic, and production upsets.

2. Check instruments and regulators

Ensure that all your existing instruments and regulators have been correctly installed and are working well. You should repair any faulty equipment, fix 'sticky' valves and check that measurement devices like sensors and probes have been properly installed, replacing them if necessary.

3. Make sure controls are working well

Check that control loops are not always set to manual and make sure operators are aware that working in automatic mode is much more efficient. Review control loops to check they're correctly configured and tuned and adjust controllers to minimise time delays and dead time.

4. Identify improvements in control

Draw up a list to show where you could save energy by improving your systems control. You should prioritise low-cost actions and enhancements and think about when to start larger projects. Identify the capital cost and payback period for each and put together an action plan for implementation.

5. Plan for implementation

Put together the business case for the implementation of your plan. This should include a feasibility study of costs and savings, a detailed risks/benefits assessment and information about the project and the project team. A pilot study could help decision-makers to give 91香蕉黄色视频 to the project.

6. Take action and improve controls

Ensure that all new control equipment is installed and calibrated properly. You should train operators to use the new systems and how to deal with unexpected performance after the changes have been made. You should also set new energy consumption targets and draw up a preventive maintenance schedule to keep controls running well and run a campaign to increase awareness of the new systems and changes that have been made among your staff.

7. Monitor performance

Set up a regular system of checks to identify any areas of poor control as early as possible, perhaps when investigating your current system. This should include reviewing operator logs for symptoms of poor control, setting performance targets and comparing them with independent benchmarks, and reviewing targets regularly to make sure they're appropriate.