Operating instructions

Functional safety

8.2 Device-specific safety instructions

SIPART PS2 with and without HART communications

108 Operating Instructions, A5E00074631-09

8.2.2 Safety function

Safety function on positioner

The safety function on the SIPART PS2 positioner is the depressurizing of the connected

valve actuator. The built-in spring brings the valve to the required safety position. Depending

on the direction of action of this spring, the valve is completely opened or closed.

This function is referred to as "tight closing" in the device documentation.

This safety function can be triggered by:

● Failure of auxiliary electrical power

● Falling below failure signal 3.6 mA at set current input (I

This also applies to failure of the pneumatic auxiliary power.

Note

Partial stroke test

If a partial stroke test is running, the safety function is only triggered if the electrical and

pneumatic power supply is switched off. The safety function is not triggered by an input

current less than 3.6 mA.

If the valve actuator cannot be depressurized on demand or in case of a fault, this represents

a dangerous failure.

WARNING

The binding settings and conditions are listed in the sections "" Settings (Page 109) and

Safety characteristics (Page 110).

These conditions must be

met in order to fulfil the safety function.

When the safety function has been executed, safety-instrumented systems with no self-

locking function should be brought to a monitored or otherwise safe status within the Mean

Time To Restoration (MTTR). The MTTR is 8 hours.

The calculated Mean Time Between Failures (MTBF) for the SIPART PS2 positioner is 90

years. The MTBF for the basic electronics module is 181 years in line with SN29500.

The characteristic service life of the valve block depends on the load. On average it is

approx. 200 million switching operations for each of the two pilot valves with symmetrical

load. The actual number of switching operations performed can be called in the local display

or via HART communication.