MACX MCR-EX-SL-RPSSI-2I(-SP)

106034_en_00

PHOENIX CONTACT

13

The probability of a dangerous failure per hour for

“continuous demand” mode and the average probability of

failure of the specified function for “low demand” mode are

determined based on the error rates:

PFD

This fulfills the requirements for the PFH value for a SIL 2

system.

When calculating the PFD

2-channel operating mode (C and D) failures of the same

cause where taken into account and a β or β

was determined.

The boxes marked in gray mean that the calculated PFD

avg

values are within the allowed range for SIL 2 according to

table 2 of IEC/EN 61508-1. They fulfill the requirement to not

cover more than 10% of the safety circuit, i.e., to be better

than or equal to 1.00E-03.

The box marked in white shows that the calculated PFD

avg

values are within the permissible range for SIL2 in

accordance with Table 2 of IEC/EN 61508-1. However, they

do not fulfill the requirement to not cover more than 10% of

this safety circuit, i.e., to be better than or equal to 1.00 E03.

Failure limit

In SIL2 applications, if the percentage of the device for the

entire safety circuit is assumed to be a maximum of 10%, a

maintenance/test interval of 4.26 years can be achieved in

this time depending on the operating mode:

Figure 7

Safety circuit

The maintenance/test interval depends on the characteristic

data of all devices involved in the safety circuit. The intervals

may be shorter or longer depending on this characteristic

data.

7.3

Condition

The values are valid under the following conditions:

–

The failure rates of the components used remain

constant throughout the period of use.

–

The propagation of errors by the device in the system is

not taken into consideration.

–

The failure rates of the external power supply are not

taken into consideration.

–

The specified error rates are based on an average

ambient temperature of +40 °C. For an average

ambient temperature of +60 °C, the specified failure

rates must be multiplied by a factor of 2.5. This factor is

based on guide values.

A

T

1 year

3 years

4 years

PFD

2.73E-04

8.19E-04

10.9E-04

PFH = 6.23 * 10

-8

/h

B

T

1 year

4 years

5 years

PFD

2.34E-04

9.37E-04

11.7E-04

PFH = 5.34 * 10

-8

/h

C

T

1 year

5 years

6 years

PFD

1.86E-04

9.29E-04

11.1E-04

PFH = 4.31 * 10

-8

/h

D

T

1 year

6 Jahre

7 years

PFD

1.47E-04

8.81E-04

10.3E-04

PFH = 3.43 * 10

-8

/h

A

3.66 years

B

4.26 years

C

5.26 years

D

6.80 years

Sensor

25%

Device

< 10%

Processing

15%

Actuator

50%