6 safety manual – JUMO 701150 14597 safetyM STB/STW - Safety Temperature Limiter and Safety Temperature Monitor Operating Manual User Manual

Page 58

6 Safety Manual

2014-05-01

The diagram above shows the different possible combinations for assessing the category with DC

avg

(horizontal axis) and the

MTTF

of each channel (bars). The bars in the diagram show the three MTTF

areas of each channel (low, medium and high)

that can be selected to achieve the required PL.
Before the simplified procedure from the diagram shown is applied (which shows the results of different Markov models on the

basis of intended architectures from section 6), the category of the SRP/CS and the DC

avg

and the MTTF

of each channel

must have been determined (see section 6 and Appendices C to E).
For categories 2, 3, and 4, sufficient measures against failures due to combined failures must be fulfilled (see Appendix F). Tak-

ing these parameters into account, the diagram represents a graphical procedure for determining the PL achieved by the SRP/

CS. The combination of category (including failures due to combined failures) and DC

avg

determines which column must be se-

lected in image 5. In accordance with the MTTF

of each channel, one of the three differently hatched areas of the applicable

column must be selected.
The vertical position of these areas determines the achieved PL, which can be read off the vertical axis. If the area covers two

or three possible PLs, the achieved PL is specified in table 7. To select the exact PL on the basis of the precise value of the

MTTF

of each channel, see Appendix K.