Flowserve 3400IQ Digital Positioner - Manual (Page 83)

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Logix 3400IQ Digital Positioner FCD LGENIM3402-00 – 0/07
flowserve.com
80 percent (present position) – 50 percent (previous) = 30 percent movement x 4-inch stroke= 1.2
inches
So, 1.2 inches is added to the travel accumulator. New dead band thresholds of 100 percent (80
percent present position plus 20 percent dead band) and 60 percent (80 percent present position
minus 20 percent dead band) are calculated. This process continues as the stem position moves
throughout its stroke range.
Cycle Counter
The cycle counter is another means of monitoring valve travel. Unlike the travel accumulator, the
stem position must do two things to count as a cycle: exceed the cycle counter dead band and
change direction. A cycle counter limit can also be written into the positioner. If this limit is exceeded,
the LEDs will blink Green, Green, Yellow Green..
Position Deviation
If the stem position differs fromthe control command by a certain amount for a given length of time,
the LED‘s will blink Red, Green, Red, Red to signify excess deviation. The trip point and settling times
are set in the transducer block.
8.13 Trend Objects
Description
Trend objects support the management and control of function blocks by providing access to history
information. Trend objects provide for short-term history data to be collected and stored within
a resource. The collected data may be input and output parameters, and status information from
selected function blocks. Trend objects are available anytime for reading.
A user will not typically view trend objects directly. A host system may receive the data and build
displays using the history data.
Logix 3400IQ Digital Positioner Trend Objects
The Logix 3400IQ digital positioner has one defined trend object.
8.14 Domain Objects
Description Domain objects support download services which are used to download firmware to a
device. Standard generic download services (defined by Fieldbus Foundation) are used in the domain
object of the Logix 3400IQ digital positioner.
8.15 Device Description
Device Descriptions and ODs
A Device Description (DD) provides a clear and structured text description of a field device. The
descriptions found in a DD supplement the object dictionary definitions of device applications. So an
OD description used in conjunction with the DD will provide a complete detailed description of the
device operation. (See the FF Fieldbus Specifications for more details about the usage of DDs and
ODs.)