Answer Posted / shreeyash nandurkar
Loop Checking
Some think of loop checking as
a process to confirm that the
components of the loop are wired correctly and is typically
something
done prior to start-up. However,
due to factors described in the
introduction above, the loop check’s
scope has expanded to also include
tests to confirm that it is “operating as designed” and then
to ongoing
programs for benchmarking and monitoring performance. The block
diagram in Figure 1-5 illustrates the
components of this expanded loop
checking process.
This process starts when the instruments are received at the
plant site.
It continues through installation and
start-up and into the ongoing plant
operation. In addition, the control system should perform
the intended
function properly. This includes
verifying the transmitter’s process
variable (PV) for display to the operator, for use in the
control strategy,
and for historical trending. This verification testing prior
to start-up is
known as the factory acceptance test
(FAT) which, as an option, can be
duplicated at site with the actual hardware and software
installed, termed
site acceptance test (SAT). Further discussed in Chapter 2,
the FAT can be
performed prior to shipment of the
hardware or in parallel with the
hardware installation
at site if the overall start-up schedule is compressed.
Once the technician checks the control strategy to verify
that the
expected output to the final control element is produced,
the loop can then
be commissioned and start-up can proceed.
Finally, the loop check can include defining the loop
performance
benchmark and providing a method for monitoring the
performance over
time.
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