A GSD file is used to identify a PROFIBUS-DP device (Master or Slave) and contains data that makes it possible to have manufacturer independent configuration. Typical information in a GSD file is Vendor based, Baudrates, Timing information, Options and features. A GSD file must be available for every DP slave.

PROFIBUS DP is an enhanced verison of PROFIBUS that has been specifically dedicated to time-critical communication between automation systems and distributed peripherals (DP).  Generally it is suitable as a replacement for the costly parallel wiring of 24 V and 4(0) to 20 mA measurement signals.

Ethernet refers to the family of local-area network (LAN) products covered by the IEEE 802.3 standard and operates using three data rates (10Mbps, 100Mbps, and 1000Mbps) currently defined for operation over optical fiber and twisted-pair cables.

Ethernet networks take on many topological configurations, but regardless of their size or complexity, all will be a combination of only three basic interconnection structures or network building blocks.   These are: point-to-point interconnection ( two network units are involved, and the connection may be DTE-to-DTE, DTE-to-DCE, or DCE-to-DCE), coaxial bus structure (segment lengths were limited to 500 meters, and up to 100 stations could be connected to a single segment), and star-connected topology (central network unit is either a multiport repeater or a network switch).

Using the interconnection structures the IEEE 802.3 standard defines a basic data frame format that is required for all implementations, plus several additional optional formats that are used to extend the protocol's basic capability. The basic data frame format contains the seven fields, these are: Preamble (PRE), Start-of-frame delimiter (SOF), Destination address (DA), Source addresses (SA), Length/Type, Data, and Frame check sequence (FCS).

.NET technologies use Web services to help enhance computing with highly integrated communications and information.  .NET benefits businesses by helping them get the most out of their existing technology investments while creating new ways to implement powerful, cost-effective information technology that will meet future needs.

NET and Web services can help businesses lower operating costs by helping connect systems; increase sales by helping employees access the right information when and where they need it; integrate services and applications with customers and partners; and lower the costs of information technology with tools that help developers quickly create new solutions to address business issues.

Just as Australian industry comes to grips with safety standard AS4024, a newer, more complex, international and now also an Australian standard is gaining wider usage.

For almost a decade, Australian industry has been applying the basic principles of Australian Standard AS4024 Safeguarding of Machinery. Those same principles: hazard identification, risk assessment and control, are reflected in the regulations of both New Zealand and Australian states and territories. Unfortunately, while awareness has grown dramatically since AS4024 was published in 1996, there is still a long way to go before there is widespread understanding of the obligations assigned by the standard.

Recently, however, the process sector of Australian industry has begun to adopt AS61508 Functional safety of electrical/electronic/programmable electronic safety related systems, the Australian version of IEC 61508. The standard, published in 1999, covers the design of Electrical/electronic/programmable electronic Safety Related Systems. It addresses the life cycle of safety-instrumented systems, risk assessment methods, change procedures for safety-instrumented systems and provides performance requirements, called Safety Integrity Levels (SIL).

On the surface, AS61508 and AS4024 have quite a bit in common. Both start with a hazard identification or analysis process, both assess the level of risk involved and both assign a "safety integrity level" or "category" to define various levels of safety performance, but that is where the similarities end.

Perhaps the biggest difference between the two standards is the measurement of risk and consequences. AS4024 uses a simple decision tree to determine which category of safety control is required. AS61508 on the other hand, asks for a quantitative measure of the overall failure rate of the safety system. The mean time between failures needs to be ascertained for each element of the system and then a cumulative probability calculated.

Theoretically, it makes sense but, in practice, the data is often very difficult to source. How can an engineer say, for example, how long a particular photo-eye will or should operate before it fails? What about the solenoids on the gates, the light curtain and the deadman controls? Without good historical data, assumptions have to be made and when you are choosing between 103 hours or 104 hours, it makes a real difference to the rating of your system.

This lack of data proved a problem for The European Commission (EC) project, STSARCES (STandards for SAfety-Related Complex Electronic Systems), which attempted to assess a machine according to IEC61508, the international standard reflected in AS61508. The report concluded:
 
"This assessment has not proven to be an appropriate way of demonstrating the effectiveness of IEC 61508... If the methodology has not been used by the manufacturer, subsequent assessment using IEC 61508 will inevitably be difficult because of missing information. However, if IEC 61508 had been followed from the outset, the relevant information would have been available, facilitating the assessment."

What it means for Australian industry?  AS61508 is here to stay and while compliance with the more manageable AS4024 will be sufficient in most cases, it makes sense to be familiar with at least the basics of AS61508. 

The categories used by AS61508 are SILs (safety integrity level), which are based on the "probability of plant failure on demand" and the consequences of failure. Probability of plant failure on demand means how often the plant is required to operate and the reliability of the system. As with AS4024, the more serious the consequences of failure, the higher the SIL, and with an increased SIL ranking comes more stringent safety system requirements.

The standard's key criteria for rating safety systems are strength, diagnostics capability, common cause strength and redundancy.

To test strength of safety hardware, an engineer must consider all the factors that could affect the operation of the system, such as radio frequency interference or even heat.

Software rated to AK6 DIN19250 (equivalent to SIL 3) for example, would include a process to check the reasonableness of data and data tables, filtering of communication messages, program flow control checking, online memory allocation testing and minimisation of real time influences by avoiding multitasking.

Diagnostic capability is measured by coverage factors, which represent the percentage of failures that will be detected. Detection rates of 60%, 90% and 99% are designated respectively as low, medium and high coverage.

Safety systems should also be designed for high immunity to common stressors. Typically, this might include isolated backplane and I/O, plus built-in diversity of processors and operating modes.

Redundancy is the final factor determining SIL ratings. Simply, the greater the redundancy and monitoring, the higher the level of safety becomes. Dual redundancy can mean, for example, that a system with a probability to fail with serious consequences once every 50 years can achieve a probability of failure of only once every 2500 years.

Despite the complexity of the detail, the basic tenets of AS61508 are simple. First, follow the safety lifecycle outlined in the standard and identify SIL requirements. When designing a safety system, look for rugged high-strength design, both in terms of hardware and software. Ensure the system has good common cause strength and the ability to tolerate and detect single failures and do not overlook the impact of field devices in SIL analysis.

VSD's must control the speed of the motor over a wide speed range. It holds the motor’s velocity signal within a specified range as a function of voltage, temperature, and load changes. Actual performance parameters include speed range and speed regulation. Other important performance parameters include motor torque, power levels, input current levels, and motor efficiency. Two control strategies are used in industry: open-loop control and closedloop control. Open-loop control depends on the electric motor’s internal regulation. Closed-loop control techniques measure the motor’s speed and compare it to the desired speed values.

Most smaller VSDs in use today continue to employ brush DC motors for a majority of applications due to their lower unit cost and ease-of-use, but technology change is on the immediate horizon. Two different VSDs — brushless PM and AC induction driven VSDs — are competing technology replacements. Both provide performance enhancements and better long-term cost savings than equivalent brush DC VSDs.

At the beginning of the design process, users may select a brushless PM VSD (employing a brushless DC motor) because they need high performance capability and are willing to pay more to obtain it. AC induction VSDs, on the other hand, are selected for longer life requirements and acquisition pricing similar to brush DC VSDs.

Emerging Pressure Points
Factory automation machines used in lower intermittent duty cycle applications will continue to use brush DC VSDs as their first choice; however, an increasing number of factory machine builders are looking at lower life cycle costs. Key elements for better life cycle costs include longer life expectancy, lower maintenance costs, better power efficiency, lower electromagnetic interference (EMI), and lower thermal stress. These elements provide the user with cost savings over a longer time period.

The rapid increase in the use of nonlinear power electronics found in today’s DC and AC VSDs has significantly increased the level of EMI in industry. Theimpact of government regulations and industry standards (FCC, IEEE, and IEC) concerning EMI levels places a premium on lower EMI performance. As a result emphasis is now placed on implementing new circuitry dedicated to minimising EMI and using electric motors with lower EMI signatures.

AC Induction VSDs
The popularity of smaller AC induction motors in lower cost and higher volume markets (appliances, vending machines, etc.) has fostered its use in VSDs in industrial and factory automation markets.

The AC induction motor is a brushless AC motor with demonstrated longer life and lower maintenance performance. Power electronics packages continue to drop in price as quantities begin to climb and the semiconductor industry’s manufacturing processes shrink electronic device size and package more components on a smaller volume of silicon. Of the many types of VSDs used, the inverter driven threephase VSD and the singlephase control VSD are currently the most popular.

The DC motor has a wider speed range and better power efficiency, but its major limitations are in life cycle costs and EMI performance. (The brush DC motor generates large amounts of EMI.) While the DC VSD has lower acquisition, installation, and operating costs, the unit life expectancy is much shorter (due primarily to motor brush life). The lower performance AC induction motors achieve the same acquisition costs as the brush DC VSD at a longer life expectancy and much lower EMI levels.

Brushless PM VSDs
Brushless PM VSDs, using either brushless PM or brushless DC motors, achieve the highest overall power efficiency over wide speed and torque ranges. (Higher motor power efficiencies lead to better energy savings.) The brushless PM motor will develop the highest power per-unit-volume, or power density, of the three motor technologies represented in this article.

Future Industry Needs
Tomorrow’s process and machine builders require an infinitely flexible VSD that can vary speeds, control torque ranges, operate at best efficiency levels, and perform under a wide range of loads, voltages, and temperatures over a longer time interval. It must simultaneously meet more stringent industry and government regulations. The enhanced performance levels of both AC induction and brushless PM VSDs provide users with improved alternatives to the venerable DC VSD.

EtherNet/IP is chosen over other protocols in the Miing Industry for the following reasons:

1. Though bandwidth requirements initially are modest, demands do increase dramatically
2. Condition monitoring will collect vibration data, which involves large file transfers
3. The incorporation of wireless Ethernet for broadband communications

Built on the standard TCP/IP protocol suite, EIP uses all the traditional Ethernet hardware and software to define an application layer protocol that structures the task of configuring, accessing and controlling industrial automation devices. Ethernet/IP classifies Ethernet nodes as predefined device types with specific behaviors. The set of device types and the EIP application layer protocol is based on the Control and Information Protocol (CIP) layers. Building on these widely used protocol suites Ethernet/IP for the first time provides a seamless integrated system from the sensor-actuator network to the controller and enterprise networks.

The needs of the factory floor are much different from the office, with some very special requirements. Instead of accessing files and printers, factory floor controllers must access data embedded in drive systems, operator workstations and I/O devices. Instead of letting a user wait while a task is being performed, factory floor data communications needs are real-time or very close to real time. Terminating the fill operation on a bottle requires much more time-precise communications than accessing the next page of an Internet site.

EtherNet/IP supports three kinds of objects the describe devices and their activity:

1. Required objects / physical characteristics of the device, such as its IP address
2. Application objects, which describe the process data
3. Vendor Specific objects

Four Kinds of Messaging are used to optimise the flow of data in the network:

1. Upload/download of parameters and setpoints; transfer of programs and recipes - Ethernet/IP uses TCP/IP (Transmission Control Protocol/Internet Protocol) for this task because this allows one-to-one communication between one device and another with full acknowledgment of a successfully received message.
2. Polled, cyclic, and event-driven data. Ethernet/IP supports all three messaging types via UDP (User Datagram Protocol, a component of TCP/IP.
3. One-to-one, one-to-many, and broadcast. UDP allows messages to be sent to many nodes simultaneously and this saves time.
4. Exchange of basic I/O, PLC style. UDP is well suited to handling I/O control data for two reasons: UDP does not require each message to be acknowledged, so speed is maximized. And unlike TCP/IP, which is one-to-one, UDP supports one-to-many node relationships

Uninterruptible Power Supplies are devices that provide battery backup when the electrical power fails or drops to an unacceptable voltage level. Small UPS systems provide power for a few minutes; enough to power down the computer in an orderly manner, while larger systems have enough battery for several hours. In mission critical datacenters, UPS systems are used for just a few minutes until electrical generators take over.

UPS systems can be set up to alert file servers to shut down in an orderly manner when an outage has occurred, and the batteries are running out.

Surge Suppression and Voltage Regulation

A surge protector filters out surges and spikes, and a voltage regulator maintains uniform voltage during a brownout, but a UPS keeps a computer running when there is no electrical power. UPS systems typically provide surge suppression and may provide voltage regulation.

Standby and Line Interactive

A standby UPS, also called an "offline UPS," is the most common type of UPS found in a computer or office supply store. It draws current from the AC outlet and switches to battery within a few milliseconds after detecting a power failure.

The line interactive UPS "interacts" with the AC power line to smooth out the waveforms and correct the rise and fall of the voltage.

Online UPS

The online UPS is the most advanced and most costly UPS. The inverter is continuously providing clean power from the battery, and the computer equipment is never receiving power directly from the AC outlet. However, online units contain cooling fans, which do make noise and may require some location planning for the home user or small office.