Safety Parameters - Beckhoff EL2904 Operating Instructions Manual

Twinsafe terminal with 4 digital fail-safe outputs

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Derating table for altitudes above 2000 m

The derating table (table 8) from the IEC 61131-2:2017 standard can be referred to for the use of the

TwinSAFE components above the specified maximum altitude.

Altitude in m

0 to 2000

3000

4000

5000

Note: Linear interpolation is permissible between the altitudes

Ambient temperature of the device at an altitude of 2000 m

The air pressure and air density increase as the altitude decreases. Therefore the derating factor for 0 to

2000 m (1.0) is used for altitudes below sea level.

Calculation example

In the following example the calculation is performed for a TwinSAFE component at an operating altitude of

4000 m.

Permissible ambient temperature up to 2000 m above sea level = 55 °C

Permissible ambient temperature up to 4000 m above sea level = 55 °C * 0.8 = 44 °C

Compliance with the temperature limits

The TwinSAFE component has a maximum internal temperature at which a switch-off takes place. This is

designed for the maximum permissible ambient temperature. If the derating factor for the temperature for

higher altitudes is used, the user is solely responsible for ensuring that the calculated maximum ambient

temperature is complied with.

3.4

Safety parameters

Characteristic numbers

Lifetime [a]

Prooftest Interval [a]

PFH

%SIL3

PFD

%SIL3

MTTF

Performance level

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