The most common terms in machinery safety

Every day we receive enquiries about our organisation, technologies, portfolio and services. An explanation of the most common terms from machinery safety is provided below.


Lifetime of products until 10 % of the product range fails “dangerously”.

Measure for the proportion of failures that have a common cause

Use of a machine in accordance with the information provided in the instructions for use, i.e. for the purpose for which it was designed – Example: A hand-held circular saw is not suitable to mount on a table and use as a circular table saw.

Failure of a device due to a common cause

Measure for the effectivity of diagnostics, may be determined as ratio between the failure rate of detected dangerous failures and the failure rate of total dangerous failures

Average diagnostic coverage

Interval between online tests to detect faults in a safety-related system that have a specified diagnostic coverage.

Different means or procedures for performing a required function.

State of an item characterised by inability to perform a required function, excluding the inability during preventive maintenance or other planned actions, or due to lack of external resources.

Part of the overall safety relating to the EUC and the EUC control system, which depends on the correct functioning of the E/E/PE safety-related systems, other technology safety-related systems and external risk reduction facilities. The primary purpose of safety technology on and in machinery is to protect people from potential hazards. At the same time it protects the environment and the actual machine from harm. Safety measures are used to isolate the hazard. The Machinery Directive and relevant standards represent the cornerstone in Europe. However, it would be wrong to regard “machinery safety” merely in terms of ticking off specified standards. Good safety solutions do not obstruct the production process, in fact they make it more efficient. They are accepted by operators – rather than inspiring them to imagine ways in which unsophisticated safety equipment might be defeated. Viewed in this way, safety technology is not an isolated but a holistic discipline, which permanently shapes the whole lifecycle of plant and machinery: Safe communication systems such as SafetyBUS p and SafetyNET p guarantee reliable connections and hold the whole system together. The terms security and safety are often confused – safety means the protection of a person (or material asset) from hazards generated by a plant or machine.

In association with computers, communication systems and automation, the term security is understood to mean any measures used to protect a system from attacks, whether accidental or intentional. The motivation for these attacks may vary, but includes espionage for example, or specific functional impairment through malware such as viruses, worms and trojans. The terms security and safety are often confused – security means the protection of a defined system, e.g. a plant or machine, from attacks or unauthorised access, whether from inside or outside. Security measures serve to immunise the machine against attacks, whether intended or unintended.

Period of time during which the device fulfils its safety function – If the mission time is exceeded, the device must be exchanged.

Classification of the safety-related parts of a control system in respect of their resistance to faults and their subsequent behaviour in the fault condition, and which is achieved by the structural arrangement of the parts, fault detection and/or by their reliability.

Average probability of failure

Probability of dangerous failure

Probability of safe failure

The Internet Protocol, IP for short, is named and used in connection with the protocol family TCP/IP. It has the important task of addressing data packets and routing them to a connectionless, packet-oriented network. For this purpose, all stations and end devices have their own address within the network, the IP address. In accordance with IP Version 4, the IP address is 32 Bits long. It is broken up into 4 Bytes and is separated by dots. For example: 127.0.0.1 Each Byte can assume a value from 0 to 255. IP V6 was launched to expand the address space, which consists of a 128 Bit address.

Average time to dangerous failure

Average frequency of operation per year

Discrete level to specify the ability of safety-related parts of a safety device to perform a safety function under foreseeable conditions.

Existence of means, in addition to the means which would be sufficient for a functional unit to perform a required function or for data to represent information. Familiar from safety (dual-channel design) or network technology with a redundant design of important communication paths to increase availability.

Risk remaining after protective measures have been taken.

Probability of dangerous failure per hour with continual use

Ratio of the overall failure rate of a device that can lead to a dangerous failure of the safety function (λ_d / λ%)

Combination of the probability of occurrence of harm and the severity of that harm

Combination of the specification of the limits of the machine, hazard identification and risk estimation.

Judgement, on the basis of risk analysis, of whether risk reduction objectives have been achieved

Real Time Frame Line, SafetyNET p version for the highest demands on the bus cycle time (up to 62.5µs) for motion control applications

Real Time Frame Network, SafetyNET p version for real-time communication with bus cycles of up to 1ms for all automation applications.

Function of the machine whose failure can result in an immediate increase of the risk(s)

Probability of a safety-related system satisfactorily performing the required safety functions under all stated conditions within a stated period of time

Security Assurance Level, measure of robustness against attacks and security incidents

Discrete level (one out of a possible four) for specifying the safety integrity requirements of the safety functions to be allocated to the E/E/PE system, where SIL 3 (SIL 4 in the process industry) is the highest level and SIL 1 is the lowest

Maximum SIL that can be claimed for an SRECS subsystem in relation to structural restrictions and systematic safety integrity

Control function implemented by an SRECS with a specified integrity level that is intended to maintain the safe state of the machine or to prevent an immediate increase in risk.

Electrical control system on a machine, the failure of which results in a direct increase in risk

Part of a control system that reacts to safety-related input signals and generates safety-related output signals

The Transmission Control Protocol, TCP for short, is part of the protocol family TCP/IP. Each TCP/IP data connection has a transmitter and a receiver. This principle is a connection-oriented data transfer. Within the TCP/IP protocol family, as a connection-oriented protocol TCP assumes the task of data security and data flow control as well as taking action in the event of data loss.

Entity of the top-level architectural design of the SRECS where a failure of any subsystem will result in a failure of a safety-related control function

See Proof test

See Mission time

The User Datagram Protocol (UDP) has the same task as TCP, only it is a connectionless protocol so it has no way of ensuring that a data packet has arrived at the receiver. These actions must be taken by higher level layers. Compared with TCP, UDP is the faster communication type.

Confirmation by examination and provision of objective evidence that the particular requirements for a specific intended use are fulfilled

Confirmation by examination and provision of objective evidence that the particular requirements for a specific intended use are fulfilled

per hour of a dangerous failure occurring See PFH

Periodic test performed to detect failures in a safety-related system so that, if necessary, the system can be restored to an “as new” condition or as close as practical to this condition. For most units, a proof test cannot be implemented for technical reasons


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