Flowserve 400MD Logix - Manual (Page 65)

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, Red, Green, 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, Red, Red, Red to signify excess
deviation. The trip point and settling times are set in the transducer block.
8.18 Trend Objects
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 infor-
mation 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.
The Logix 3400MD digital positioner has one defined trend object.
8.19 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 3400MD digital positioner.
8.20 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.)
DD Download
The DD for the Logix 3400MD digital positioner can be downloaded by going to the Software Download section on the Flowserve website at www.flowserve.
com .
Device Description Contents
A typical DD contains information about the device parameters and operation, such as:
• Attributes, like coding, name, engineering unit, write protection, how-to-display, etc.
• The menu structure for listing parameters, including names of menus and sub-menus.
• The relationship of one parameter to others
• Information about help text and help procedures
• Maintenance, calibration and other necessary operation information.
Logix 3400MD Digital Positioner LGENIM3405-02 11/13
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