Flowserve 1400 Valtek Logix - Manual (Page 20)

46-20 Flowserve Corporation, Valtek Control Products, Tel. USA 801 489 8611
1400 digital positioner keeps a running total of valve
movement. When the positioner first powers up, high and
low dead-band limits are calculated around the present
position. When the stem position exceeds the travel
dead-band, the movement from the center of the dead-
band region to the new position is calculated and added
to the travel accumulator. From this new position, dead-
band high and low limits are again calculated.
Example: The Logix 1400 digital positioner has a default
dead-band configuration of 20 percent. The valve has a
4 inch linear stroke. When the valve first powers up, the
command signal is 50 percent. The unit will calculate a
high travel threshold of 70 percent (50 percent present
position plus 20 percent dead-band) and a low travel
threshold of 30 percent (50 percent present position
minus 20 percent dead-band). As long as the stem
position remains greater than 30 percent and less than 70
percent, no additions are made to the travel accumulator.
Now, assume the stem position moves to 80 percent
which is outside the present dead-band. The Logix 1400
digital positioner calculates the stem movement and
adds this number to the travel accumulator.
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 yellow LED will blink.
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.
Advanced Features
Note: These features are contained in the transducer
function block.
Standard vs. Advanced Diagnostics
Advanced diagnostics models add top, bottom, and
supply pressure sensors. This allows for more diagnos-
tic calculations such as loss of pressure, advanced
signatures, and troubleshooting.
Temperature and Pressure Units
The desired temperature and pressure units can be set
during configuration. Once set, all readings will be dis-
played in the desired units.
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 accu-
mulator 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 accumu-
lator 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.
Custom Characterization
Custom characterization can be thought of as a ‘soft
CAM.’ The user can choose between a linear, equal
percent, quick-open, or custom user-defined character-
ization curve using 21-points. The control will linearly
interpolate between points. Points do not have to be
equally spaced in order to allow more definition at critical
curve areas.
The Logix 1400 digital positioner has two modes: linear
and custom characterization. Linear is a straight 1:1
mapping of command to control command. It does not
use the 21-point curve definition. When custom charac-
terization is
disabled, the positioner is automatically in
Linear mode. If custom characterization is enabled, the
Logix 1400 digital positioner uses a 21-point defined
curve.
The Logix 1400 digital positioner comes with a factory-
default equal-percent and quick-open curve as shown in
Figure 18.
Stroke Characterization
In addition to two pre-defined and embedded character-
ization curves, the Logix 1400 digital positioner has a 21-
point custom stroke characterization feature. This al-
lows the user to define a unique set of operating param-
eters customizable to his process conditions.
Characterization Procedure
The following procedure outlines the basic way setting up
a custom stroke characterization takes place.
1. Verify the process is in a safe condition and that the
valve may be taken out of service.
2. Put the Transducer block MODE_BLK in OOS (Out
Of Service)