Operation And Maintenance; Proof Test Without Automatic Testing; Testing The Instrument - ABB LLT100 Functional Safety Manual

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C h A P T E R 5

Operation and maintenance

Proof test without automatic testing

In accordance with IEC 61508, the safety function of the measuring device must be checked at
appropriate time intervals. The operator must determine the proof test interval and take this into
account when determining the PFD
such a way that it verifies correct operation of the device.
Testing of fixed output current, HIGH and LOW alarm output current and measuring accuracy are
covered in the proof test. Testing the device can be performed by following the steps described

Testing the instrument

To check the safety function of the device, proceed as follows:
1 Verify and record the conditions as they are found prior to checking the safety function: write
protection is on/off, instrument parameters.
2 Remove the device from its installation flange. Perform a visual inspection and record any visible
defects or wear outs. Its optical interface (glass) shall be inspected and cleaned.
3 Bridge the safety DCS or take other appropriate measures to prevent inadvertent triggering of
alarms.
4 Deactivate write protection (see "Commissioning" on page 19).
5 Performing the proof test requires the specified voltage input (see "Alarm response and current
output" on page 12) in series with an ammeter (see Figure 2).
value of the laser level transmitter. The test must be carried out in
AVG
below.