Emerson Fisher FIELDVUE DVC6000f, Инструкция по эксплуатации

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F
OUNDATION
Fieldbus Communication
December 2009 D-7
Figure D-3. Simple Single-Link Fieldbus Network
Fieldbus Segment
LINK MASTER
BASIC DEVICES
LAS = Link Active Scheduler
LAS
B2712-1 / IL
Transducer Block Status and Limit
Propagation
Every FOUNDATION fieldbus parameter has a value
and a status. The status attribute is divided into three
components: Quality, Quality substatus, and a Limit.
The Quality can be Good (Cascade), Good
(Non-Cascade), Uncertain, and Bad. Each quality can
have a substatus as shown in table D-3. Each status
attribute also has four possible limit states: Not limited,
Low limited, High limited, and Constant. Refer to the
Fieldbus Foundation specifications for a more detailed
description. The following describes how the
transducer block passes status information to the AO
block. For information on status handling by the
function blocks within the digital valve controller, refer
to the Detailed Setup section.
Status Propagation
The transducer block accepts the output from the AO
block or DO block if the output parameter status is
Good (Non-cascade) or Good (Cascade). When the
AO or DO block is Out of Service the output
parameter status is Bad. In this case, the transducer
block holds the last value.
If the transducer block actual mode is Out of Service,
the AO block READBACK parameter status is
Bad
−
Out of Service. This could be caused by a Failed
Alert. If a Failed Alert is active, the block error
parameter (parameter name BLOCK_ERR) for the
Resource block will indicate Device Needs
Maintenance Now. For more information on the
Resource and Transducer block error indications, refer
to the Viewing Device Information section of this
manual.
If the transducer block is functioning correctly the AO
block READBACK parameter status is Good
(Non-cascade)
−
Non-specific. If a Maintenance or
Advisory alert is active the substatus will reflect a
Unacknowledged or Active advisory alert. When a
Maintenance or Advisory alert is active, the block error
for the resource block indicates Device Needs
Maintenance Soon.
Limit Propagation
The following describes limit propagation:
AO Block
If the valve position is below the low cutoff value,
the AO block READBACK status limit is
LOW_LIMITED.
If the valve position is above the high cutoff
value, the AO block READBACK status limit is
HIGH_LIMITED.
If the transducer block actual mode is Auto and
the above conditions are not true, the AO block
READBACK status limit is NOT_LIMITED.
If the transducer block actual mode is Out of
Service, the AO block READBACK status limit is
CONSTANT.
DO Block
If the transducer block actual mode is Auto, the
DO block READBACK_D status is NOT_LIMITED.
If the transducer block actual mode is Out of
Service, the DO block READBACK_D status is
CONSTANT.
The control strategy should be configured to monitor
the Analog Output block status and take action where
appropriate when the status is no longer Good.
D