Technical information

IM-P343-29 CH Issue 546
9.6.1 dbANd - deadband setting (positional sensitivity)
Programming notes
Dead-band provides adjustment of the valve positioning sensitivity relative to
the input signal and is expressed as a % of the input signal span.
Default value based on a 4 - 20 mA input signal span is 0.5% with a minimum
setting of 0.2%.
Note: 3% may be displayed if ACT is set to 'ON'. Refer to
Section 9.5.2, page 39.
These values may change if the input signal span is reduced i.e. for a 4 mA input
signal span the default and minimum setting is 0.8%.
The maximum setting is 10% of the input signal span.
To alter the displayed value press and keys. Press key to accept the
displayed value and advance to the shut-off minimum (S-MIN).
Commissioning notes
Setting a narrow deadband may induce oscillations of valve movement caused by fluctuations
in the input signal, high stem friction or operating at low ambient temperatures below 0
°C.
Setting a wider deadband will dampen out oscillations but may cause an inaccuracy in actual
valve position. This effect will increase if valve travel is limited. It is normally recommended
that the default value is used. If necessary gradually increase the % value to dampen out any
oscillations in valve movement. This may be necessary for valves having graphite packed stem
seals or smaller size actuators where typically a deadband of 4% may be required.
9.6.2 S-MIN - valve shut-off - minimum travel
Programming notes
Provides the facility to fully vent the actuator at a predetermined input signal.
The value set is a percentage of the input signal span range, i.e. setting a
value of 10% with an input span range of 4 - 20 mA (span 16 mA), will cause
the valve to close with an input signal of 5.6 mA i.e. 4 mA + 1.6 mA (10% of
16 mA). Maximum setting is 20%.
Default values will depend on the selection of valve type (2-port or 3-port)
and control action (direct or reverse) as follows:
Valve type Direct Reverse
2-port 0.1% Off%
3-port 0.1% 0.1%
For direct control action (dIRCT) can only be set if MIN-T = 0% (will vent the
actuator at set value). For reverse action (REV) can only be set if MAX-T = 100%
(will inflate the actuator at set value).
Press and keys to alter the displayed value. Press key to accept the
displayed value and advance to shut-off maximum (S-MAX).
Commissioning notes
With an actual input signal equivalent to minimum input signal span range (MIN-R) it
may cause the valve plug to hover over the seat preventing tight closure with the possibility
of erosion damage to the plug and seat faces. Setting a shut-off value can help prevent
this by providing early closure of the valve.