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Z1

Z1

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Then comes single-channel architecture with diagnostics. In this case, a module called Test Equipment (TE) provides an output (OTE) in some way

linked to the status of the safety function:

Were:

im

: interconnection means

I

: input device, e.g. sensor

L

: logic

m

: means of surveillance

O

: output device, e.g. valve

OTE

: Test Equipment OUTPUT

TE

: Test Equipment

A third example is double-channel architecture, which exploits the redundancy of a function – if one channel fails the other remains active:

Were:

im

: interconnection means

I1, I2

: input device, e.g. sensor

L1, L2

: logic

m

: means of surveillance

O1, O2

: output device, e.g. valve

c

: crossed check

As regards the conformity of components used to the basic and/or proven safety principles, reference should be made to a series of considerations

presented in EN ISO 13849 standards, which guarantee that the SRP/CS and related components comply with the design, construction and assembly

principles.

With these data, the machine designer can determine the safety function category (B, 1, 2, 3 or 4, in increasing order of importance) and the PL

achieved; It is important therefore to check it is equal to or greater than the PLr required.

SAFETY COMPONENTS: OVERVIEW OF THE STANDARDS