Tab Safety-related values

Miscellaneous standards and guidelines (e.g., the machinery directive 2006/42/EC) require that the probabilities of failure be calculated for machines and safety functions. For this reason, the manufacturers of devices state safety-related values for their devices / components. For example, the value "MTBF" indicates the frequency with which a device fails or supplies incorrect results (MTBF: short for "Mean Time Between Failures").

A complete higher-level function involves a large number of devices with differing safety-related values. Depending on usage, there are differing values for the failure of such higher-level function for the overall higher-level function. These values are calculated by way of auxiliary programs following the planning. The values of all devices used must be known for the calculation.

Enter the safety-related values in this tab. This data can be specified several times per part.

Note:

We recommend no longer using the properties of the safety-related values since these will no longer be supported in the future. These properties only exist for reasons of compatibility.

Tip:

But easier and more convenient than the manual capture of the values is the import into parts management. The device manufacturers provide the safety-related values in the standard XML exchange format of VDMA. (The abbreviation "VDMA" stands for "Verband Deutscher Maschinen- und Anlagenbau" and designates the association of machine tools and plant engineering in Germany.) In order to add safety-related values to existing parts, the Import records dialog includes the "VDMA 66413" file type. Via this entry, you can import XML files with safety-related values that are set up according to the VDMA exchange format.

Overview of the main dialog elements:

Use cases:

The usage of a device is known as a so-called "use case". Each use case has its own set of safety-related values. This means that, depending on how a device is used, differing safety-related values must be used. Differing uses cases may be derived, for example, from the differing use of a device. Thus, for example, a drive can be operated with or without brakes, which in turn means differing safety-related values.

The use cases can be structured in up to five hierarchical levels. There must be at least one hierarchical level. The safety-related values are located at the lowest hierarchical level. If use cases have hierarchical levels with the same designation, this creates a tree-like structure.

Example:

Hierarchical level 1	Hierarchical level 2	Hierarchical level 3
Drive 1
	without a brake
		1-channel
		2-channel
Drive 2

The two use cases Drive 1 > Without a brake > 1-channel and Drive 1 > Without a brake > 2-channel differ at the third hierarchical level. The safety-related values are located at this hierarchical level. The figure above illustrates the tree-like structure.
In a use case that has only one hierarchy level (e.g., Drive 2), the safety-related values are located at this one hierarchy level.

Input (Collect) / Logic (Generate report) / Output (React):

Function ranges (safety-relevant parts of controls, subsystems) of the safety function: The relevant device is assigned functionally within the safety function on the basis of this division; for example, a position switch is identified as input ("collect"). Please note that at least one of these function ranges must be selected for each use case.

Safety-related values:

The following abbreviations are used in the fields for the actual safety-related values:

PL: Indicates the ability of safety-relevant parts of a control to carry out a safety function under foreseeable conditions (short for "Performance Level").
MTTF: Mean time to failure (short for "Mean Time To Failure").
SIL CL: SIL limit (short for "Safety Integrity Level Claim Limit"). The safety integrity level SIL (short for "Safety Integrity Level") specifies the requirements of the safety functions of a control system. Level 1 denotes the lowest requirements; Level 4 the highest. The SIL claim limit is the maximum SIL required for a subsystem.
MTBF: Mean time between failures (short for "Mean Time Between Failures").
PFHD: Average probability of a dangerous failure (short for "Probability of dangerous Failure per Hour").
RDF: Ratio, in percentage, of failures in terms of total failures (short for "Ratio of Dangerous to all Failures").
TMT1: Duration of use, "Mission Time"; proof-test interval.
B10: Mean number of cycles up to which 10% of the components have failed.
MTTFD: Mean time to dangerous failure (short for "Mean Time To dangerous Failure").
B10D: Mean number of cycles up to which 10% of the components have failed dangerously.
Lambda-D: Rate of dangerous failures.

Popup menu:

The popup menu provides - depending on the field type (e.g. date, integer, multilingual) - the following menu items that are, depending on the situation, available for influencing the table or editing the values in the fields. You can find an overview of these popup menu items in the section Popup menu items.