SafetyNET p

Key takeaways

SafetyNET p belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect SafetyNET p to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of SafetyNET p from memory before moving on to harder problems.

Reference excerpt

SafetyNET p is a standard for Ethernet-based fieldbus communication in automation technology. SafetyNET p is suitable as a drive bus due to its real-time behaviour, with cycle times of up to 62.5 μs. In accordance with the standard requirements from EN 61508 and EN 61511, it can be used in safety circuits up to and including Category 3, SIL 3.

Origin SafetyNET p is a registered trademark of Pilz GmbH & Co. KG and was presented in public for the first time in 2006. Its objective was to enable fieldbus communication on Ethernet in real-time and to simultaneously provide data communication in terms of machinery safety. SafetyNET p combines safety and automation: it is both a safety and an automation fieldbus and as such is the successor to SafetyBUS p. The SafetyNET p technology is managed through the umbrella organisation Safety Network International e.V.

Application In addition to its use as an Ethernet-based fieldbus, a key component in the application of SafetyNET p is the communication of data with a safety-related content. SafetyNET p can be used anywhere that communicated data has to be consistent in terms of time and content, in order to safeguard against danger. This danger may concern hazards to life and limb, but may also involve the protection of economic assets. A second application area is the communication of data in real-time. With bus cycle times of up to 62,5 μs, SafetyNET p can even be used in extremely time-critical areas. Typical application areas are:

Factory automation (e. g. car production, presses) Transport technology (e. g. cable cars, fairground rides) Drive technology (e. g. sensor/actuator control loop in drives or industrial robots) In general, all automation and process engineering applications are possible.

Technology SafetyNET p is based on Ethernet. There are two different but compatible versions of SafetyNET p.

RTFN RTFN (Real time frame network) uses conventional Ethernet IP frames for communication. The mechanisms for security and real-time are located on OSI levels 3 and above. A producer-consumer model is used as the communication principle. A central process controller (PLC) is not required. This enables concepts such as modular engineering, for example. SafetyNET p RTFN is fully compatible with all IP-based Ethernet protocols and can be combined on the same medium. Conventional switches, routers and wireless access points can also be used. A system cycle time of around 1 ms can be achieved, depending on potential competing services. If higher performance is required, SafetyNET p RTFL can be used.

RTFL RTFL (Real time frame line) uses Ethernet MAC frames for communication. A producer-consumer model is also used at logical level on RTFL. In order to achieve the required performance, communication takes place in optimised Ethernet MAC frames. The first subscriber in the logical line sends an Ethernet MAC frame to its logical neighbour, which completes its part of the frame and then passes the frame along the logical line to its nearest neighbour. This way all subscribers fill in the frame in succession. The last subscriber in the line sends the completed frame back to the first subscriber using the same channel (via all the subscribers). In the process, individual subscribers can remove the data they need as the frame passes through. System cycle times in the area of 62.5 μs can be achieved. SafetyNET p subscribers can pack miscellaneous IP-based traffic within an RTFL frame as part of real-time communication.

Technical details The SafetyNet p frame data, as determined by the technology, is as follows:

Compatible with Ethernet IP protocols Networks can be designed in a linear, star or tree topology Networks with variable subscribers can be used thanks to the continuous topology scan The maximum distance between two subscribers corresponds to that of conventional Ethernet (this is 100 m when copper cables are used) With RTFN, the number of bus subscribers is limited only by the IP address space With RTFL you can have 512 bus subscribers per segment Guaranteed system cycle times of up to 62.5 μs can be achieved Suitable for applications in accordance with SIL 3 of IEC 61508 SafetyNET p is assigned port number 40000 on IANA’s "List of assigned port numbers".

Organisation The user organisation Safety Bus p Club International e.V. combines manufacturers and users of SafetyBUS p and has been in existence since 1999. In 2006 the organisation was renamed Safety Network International e.V. In addition to the international organisation there are also two other regional organisations: Japan was established in 2000, while the United States was established in 2001.

Literature Winfried Gräf: Maschinensicherheit. Hüthig GmbH & Co. KG, Heidelberg 2004, ISBN 3-7785-2941-2 Arbeitspapier der BIA: Prüfgrundsätzen für sichere Bussysteme. EU Maschinenrichtlinie: 98/37/EG Safety Network International: SafetyNET p Systembeschreibung Version 2.0

References

Worked examples

Example 1 — a first encounter with SafetyNET p

Start with the simplest possible case. Write down what SafetyNET p claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to SafetyNET p before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about SafetyNET p ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of SafetyNET p

In research: SafetyNET p appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses SafetyNET p in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: SafetyNET p is common in secondary-school and first-year university syllabi. It links to neighbouring topics Industrial Ethernet, Safety, so understanding it makes those chapters shorter.
In everyday life: Look for SafetyNET p outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study SafetyNET p in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what SafetyNET p means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain SafetyNET p out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is SafetyNET p in simple terms?

SafetyNET p is a standard for Ethernet-based fieldbus communication in automation technology. SafetyNET p is suitable as a drive bus due to its real-time behaviour, with cycle times of up to 62.5 μs.

Why does SafetyNET p matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study SafetyNET p?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on SafetyNET p.