Instrumentation & Measurement Magazine 25-7 - 11

◗ Quality: Indicates the quality of the value field. Quality
= " Good Cascade " means that the value is good, and
it may be part of a cascade path. Quality = " Good NonCascade "
means that the value is good, and the block does
not support a cascade path. Quality = " Uncertain " means
that the quality of the value is less than normal but may
still be useful. Quality = " Bad " means that the value is not
useful at all.
◗ Sub-status: The sub-status is a complement of the quality
status and takes information to initialize or break a
cascade path. There are different sets of sub-status for
each quality, as listed in Table 2.
◗ Limits: Provides information whether the associated
value is limited or not, as well the direction. The limits
are classified as " Not Limited, " " High Limited, " " Low
Limited, " and " Constant. "
In normal conditions, the PID and AO blocks work in cascade,
with the AO block following the output of the PID block,
and the PID block checking the feedback given by the AO
block. The cascade is broken if the sensor or the actuator fails,
or if the communication links between the blocks are cut. If the
sensor fails, or the connection AI → PID is lost, the following
sequence of events occurs:
◗ The IN input of the PID block goes " Bad, " signaling a fault
in the sensor or a communication error with the upstream
block.
◗ The PID block sends a " initiate fault state " request to the
downstream block (OUT.Status.Sub-status = 0xe0).
Table 2 - Status bits according to FF specifications
Quality
Sub-status
Lowest priority
Good (NC)
Good (NC)
Good (NC)
Good (NC)
Good (NC)
Good (NC)
Good (NC)
Uncertain
Uncertain
Uncertain
Uncertain
Uncertain
Uncertain
Uncertain
Good (C)
Good (C)
Good (C)
Good (C)
Good (C)
Good (C)
Good (C)
Good (C)
Highest priority
October 2022
Bad
Bad
Bad
Bad
Bad
Bad
Bad
Bad
NC = non-cascade ; C = cascade
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11
0 = non-specific
1 = active block alarm
2 = active advisory alarm
3 = active critical alarm
4 = unacknowledged block alarm
5 = unacknowledged advisory alarm
6 = unacknowledged critical alarm
0 = non-specific
1 = last usable value
2 = substitute
3 = initial value
4 = sensor conversion not accurate
5 = engineering unit range violation
6 = sub-normal
0 = non-specific
1 = initialization acknowledge (IA)
2 = initialization request (IR)
3 = not invited (NI)
4 = not selected (NS)
5 = local override (LO)
6 = fault state active (FSA)
7 = initiate fault state (IFS)
0 = non-specific
1 = configuration error
2 = not connected
3 = device failure
4 = sensor failure
5 = no communication, with last usable value
6 = no communication, with no usable value
7 = out of service
Hex value
0x80
0x84
0x88
0x8c
0x90
0x94
0x98
0x40
0x44
0x48
0x4c
0x50
0x54
0x58
0xc0
0xc4
0xc8
0xcc
0xd0
0xd8
0xdc
0xe0
0x00
0x04
0x08
0x0c
0x10
0x14
0x18
0x1c
Instrumentation & Measurement Magazine 25-7

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