Flowserve 3400IQ Digital Positioner - Manual (Page 36)

Logix 3400IQ Digital Positioner FCD LGENIM3401-00 – 06/06
36
ExAMPLE: The Logix 3400IQ 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 that is outside the present dead-band. The Logix 3400IQ 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.
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 Features
NOTE: These features are contained in the transducer function block. Refer to the 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 more
diagnostic calculations such as loss of pressure, advanced signatures, and troubleshooting.
7.14.9 Temperature and Pressure Units
The desired temperature and pressure units can be set during configuration. Once set, all readings
will be displayed in the desired units.