IM-P343-35 CTLS Issue 5
53
SP500 Electropneumatic Smart Positioner
9.6.1 dbANd - deadband setting (positional sensitivity)
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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 45.
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
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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.
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