The reason for my question is:
- The PLC is definitely a critical component of
automation, though maybe with varying impact,
based on the purpose of the machine/process it
controls. 21CFR11 and GAMP seem to require that
the PLC hardware and software including control
panels, Man machine interface, Ladder logic, etc.
be validated ( ref. PPT presentations from the
internet that I cannot attach in this reply as
LISTserv may reject the mail). PLC
ladder diagrams and code as you know are analogous to
lines of code of application software .
2.Towards this end, most in house or third party based
validation seems to undertake ONLY the
communication test. In this test, the PLC
communication cable is connected to the PC which is
loaded with the manufacturer’s software and wires
disconnected / reconnected to check that
individual functions are controlled.
This done as part of IQ/OQ/PQ.
However, this does not provide any useful information
towards preventive action (impending
failure of PLC and associated circuitry). Nor does it
provide any information on change in process timings
due to aging of / defective components,unlike waveform
distortion and timing monitoring. In situ
communication tests can anyway be performed without
the communication cable, by merely disconnecting the
very same wires indicated in the machine’s manual.
The pharma equipment operator / scientist is no
service engineer not does he have to play the
role of one. However, where validation requires an
electrical/electronics engineer to perform
certain checks, the service of the latter must be
In many situations the end result does not necessarily
validate the process since successful end results may
not evaluate possible failure situations ( preventive
action situations) that could affect quality.
Most of the time I come across discussions on
inadequacy of documentation rather than on actual
tests required for hardware validation, corrective and
preventive action, their adequacy/inadequacy, etc. The
depth and nature of supporting information requested
also seems to depend on the auditors themselves. Of
late the software and PLC validation aspects seem to
be drawing more attention than earlier.
In the light of the above I wish to know what the
stand of the ISPE is:
Is it necessary to test GMP critical hardware from the
Preventive and corrective action angle (waveform test)
or is it sufficient to test the same merely for ideal
case functionality (communication test)
or is it sufficient to go by only the documented end
results of the process that the machine performs.