21
3.7 Functional test
With operation of the device at a higher demand rate, e.g. with process-related frequent activation of the
device, additional functional testing can be omitted in accordance with IEC 61508. This also applies for
operation with a low requirement rate, i.e. infrequent activation of the device due to process conditions. The
probability of failure is very low for a service life of 10 years according to SIL2 (see table on page 20).
The temperature probe is replicated with a simulator for a functional test. The inputs can be
connected in parallel for thermocouples.
The test begins with a check of the temperature monitoring. The relay must be active in the good range.
Then a check
-
takes place to determine whether the temperature on the display of the STL4896 matches the
temperature of the simulator for each test step
-
the alarm function when the good temperature range is violated
-
the alarm function in case of a probe break (each cable separately) and probe short-circuit.
Correct alarm function of the STL4896 is provided if
-
the relay is deactivated and the contact switches to rest position,
-
the error is shown correctly in plain text on the display,
-
the LED alarm on the front of the STL4896 illuminates,
-
a voltage of 24 V DC is connected to the appropriate terminals for an external alarm.
After the simulator changes the temperature back to the good range, the STL4896 functions correctly if the
relay is reactivated, in safety temperature limiter operating mode,
-
the relay is not activated until the front RESET button or an external RESET button having been
pressed,
-
then the display shows the normal operating data,
-
the LED alarm on the front of the STL4896 goes out,
-
and voltage is no longer connected to the terminals of the external alarm.
in safety temperature limiter operating mode,
-
the relay is activated without the front RESET button or an external RESET button having been
pressed,
-
the display shows the normal operating data,
-
the LED alarm on the front of the STL4896 goes out,
-
and voltage is no longer connected to terminals 11 and 10.
Attention!
If the relay is not deactivated during one of the test steps or temperature and/or causes of error
are not displayed correctly, the STL4896 must be sent to the factory for inspection. In the
meantime, the system must be kept in a safe state by other means.
Special notices!
-
The STL4896 safety temperature limiter must be installed in a switch cabinet with a
protection rating of at least IP40.
-
Strain relief for the connecting cable(s) of the temperature sensor must be provided.
-
As protection for the internal device fuse of the STL4896, securing the monitoring current circuit
with
an
external fuse (maximum 1.6 A, medium time lag) is recommended. If the internal fuse is tripped,
the device
must
be sent to the factory for service!
DANGER
