Flowserve Logix 1200e LGAIM0044 - Manual (Page 39)

Flowserve Corporation, Valtek Control Products, Tel. USA 801 489 8611 44-39
Soft Limits
Unlike position alerts, soft limits prevent the stem posi-
tion from moving below or above the configured limits.
If the command signal is trying to drive the position
past one of the limits, the yellow LED will blink but the
stem position will remain at the set limit.
Q: Will soft limits prevent the valve from going to its fail
position?
A: No.
Position Alerts
Position alerts notify the user the valve has traveled
past a configured limit. The default settings are -10
percent and 110 percent, which are outside normal
travel and therefore disabled. Position alerts only
notify the user a limit has been exceeded and do not
limit stem movement. Position alerts will cause the yel-
low LED to blink.
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: 1)
exceed the cycle counter dead band and 2) change
direction. A cycle counter limit can also be written into
the positioner. If this limit is exceeded, the yellow LED
blinks. The cycle counter must be reset to begin a new
count sequence. This must be done after the alert has
been triggered to reset the alert. Do this by clicking on
the reset button in ValTalk or SoftTools software in the
configuration section of the software. With the HART
275 handheld communicator, resetting is accom-
plished by choosing Configure (3) Cycle/Travel Inf. (9),
Cycle/Travel, Cycle Information (2), Reset Cycle
Counter (4).
Travel Accumulator
The travel accumulator is similar to an automobile
odometer and sums the total valve movement. Using
the user-defined stroke length and travel dead band,
the Logix 1200 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 cal-
culated.
For example, the Logix 1200 positioner has a default
dead band configuration of 20 percent. The valve has
a 4-inch (10 cm) 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 per-
cent 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. At this point, assume
the stem position moves to 80 percent, which is out-
side the present dead band. The Logix 1200 posi-
tioner calculates the stem movement and adds this
number to the travel accumulator.
80% (present position) – 50% (previous) =
30% movement x 4-inch stroke = 1.2 inches
Therefore, 1.2 inches (3 cm) is added to the travel
accumulator. New dead band thresholds of 100 per-
cent (80 percent present position plus 20 percent
dead band) and 60 percent (80 percent present posi-
tion minus 20 percent dead band) are calculated. This
process continues as the stem position moves
throughout its stroke range.
The travel accumulator will need to be reset to begin a
new count sequence. This must be done after the alert
has been triggered to reset the alert. Do this by click-
ing on the reset button in ValTalk or SoftTools software
(in the Configuration section of the software) With the
HART 275 handheld communicator, resetting is
accomplished by choosing Configure (3) Cycle/Travel
Inf. (9), Cycle/Travel, Travel Information (2), Reset
Travel Accumulator (4).
Position Deviation
If the stem position differs from the control command
by a certain amount for a given length of time, the yel-
low LED blinks to signify excess deviation. The trip
point and settling times are set from the Configuration
screen of ValTalk and SoftTools software. It is set in
the HART 275 handheld communicator under Config-
ure (3), Position Alerts (9), Deviation Deadband (3)
and Time (4).