Logix 3400MD Digital Positioner FCD LGENIM3404-00 – 9/09
22
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.
7.14.5 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 yellow LED will blink.
7.14.6 Position Deviation
If the stem position differs from the control command by a certain
amount for a given length of time, the yellow LED will blink to signify
excess deviation. The trip point and settling times are set from the
transducer function block.
7.14.7 Advanced and Features
NOTE:
These features can be activated for full diagnostic functionality of
the system. These are contained in the transducer blocks. Refer to the
Installation and Reference Manual for a more detailed explanation.
7.14.8 Standard vs. Advanced Diagnostics
Advanced diagnostics models add top, bottom, and supply pressure
sensors. This allows for diagnostic functionalities such as loss of
pressure, advanced signatures, etc. Pro diagnostics adds the full
compliment of diagnostic features offered by the Logix 3400MD.
7.14.9 Temperature and Pressure Units
The desired temperature and pressure units can be set during configu-
ration. Once set, all readings will be displayed in the desired units.
7.14.10 Stroke Length
Stroke length is used by the travel accumulator. When the stroke
length and units are set, the length is used to determine the total travel
accumulated. The travel accumulator will have the units associated with
stroke.
ExAMPLE:
Stroke length is set to four inches. If the valve is moved
from 0 percent to 100 percent, four inches will be added to the travel
accumulator. The travel accumulator units will be inches. If Stroke
length is 90 degrees for a rotary, the travel accumulator will now have
units of degree. A 0 percent to 100 percent stroke will add 90 to the
travel accumulator.
NOTE:
Stroke length is for information only and is not used during
calibration.
Table IX: Transducer Block Characterization Parameters
Parameter
Description
Value - Meaning
Comments
MODE_BLK The operating
mode of the
transducer block
Auto - Auto (target
mode)
The transducer
block must be out
of service before
characterization can
be edited or changed
OOS - Out of
Service
CURVE_
SELECT
Selects the
characterization
curve type when
the DIP switch
is set to ‘Other’.
This parameter
is inactive when
the DIP switch
is selected to
‘Linear’.
0 - Equal Percent
Sets the charac-
terization to equal
percent mode.
1 - Quick Open
Sets the character-
ization to quick open
mode.
2 - Custom
Sets the character-
ization to use the
curve fit param-
eters CURVEX and
CURVEY.
USER_
INTERFACE_
ACTIVE
Software version
of the physical
DIP switches.
The parameters
can be changed
either in the
parameter or at
the device via the
DIP switches.
1 - Air Action
2 - Characterization
Linear
3 - Rotary Actuator
Gain
Select 1=ATO or
0=ATC
Select 1=Linear or
0=Other
Three bits of the
prameter reflect the
value selected on the
Rotary Actuator Gan
switch as follows:
A=111, B=011,
C=101, D=001
E=110, F=010,
G=100, H=000
CURVEX
Numeric X value
array for custom
point. (1 x 21
array points)
X-axis value for
custom stroke
characterization
point. Range –10
to 110
Pair each X-value
with corresponding
Y-value to define
the desired point.
Values must be in
ascending (or equal)
order.
CURVEY
Numeric Y value
array for custom
point. (1 x 21
array points)
Y-axis value for
custom stroke
characterization
point. Range –10
to 110
7.15 Characterization Retention
Once a custom curve has been loaded into the Logix 3400MD digital
positioner’s memory it is retained in the EPROM until it is either edited
or replaced. Turning Custom Characterization Active on or off now
selects between a linear response (off), or the new custom curve (on).
If either of the other two factory curves is selected it will overwrite
the custom curve in RAM only. The custom user-defined curve will
automatically be activated again when the factory curve is deselected.
