Industrial Communication Systems

Functional Safety 21-11

According to [PHO97], the probability of a bit being destroyed on shielded twisted pair cables is p = 10

−5

.

It is assumed that v = 10 safety-related messages are sent every second. e rate of single bit transmission

error U is

U p v

1

4

10= =

−

* /s (21.1)

In

other

words,

every

10,000

s,

a

single

transmission

error

occurs

and

the

risk

of

a

single

bit

being

destroyed

per

second

is

10

−4

. e probability that two bits are destroyed within 1 s is 10

−9

, assuming that

probabilities

are

independent

and

therefore

p

2

is inserted into the aforementioned formula instead of p.

As

a

result,

the

safety

integrity

of

a

safety

measure

must ...