PCC-IV Instruction Manual (Rev. 0.1)
Page 6-30
Section 6
– Blockware Functions
Technical Reference
procedure (see 'Actuator Setup' above). The Scaled Position must be calibrated whenever the actuator is initially
installed, changed-out, re-stroked, or if the feedback pot is changed.
Using the
Change one output
Service Manual submenu, press and hold the DEC key until the actuator is fully closed
(0% position). Use the Browse Blocks menu (see Section 4) to display the unscaled FEEDBACK INPUT (
I
02) value
of this
TOUT
Block. Enter this value into Parameter 4 (Feedback % at 0% Position).
Using the
Change one output
Service Manual submenu, press and hold the INC key until the actuator is fully open
(100% position). Use the Browse Blocks menu (see Section 4) to display the un-scaled FEEDBACK INPUT (
I
02)
value of this
TOUT
Block. Enter this value into Parameter 5 (Feedback % at 100% Position).
Deadband %, Parameter 7 (Positioner mode): This value must be adjusted individually for each actuator to minimize
hunting (due to the connected load and the effectiveness of the actuator's brake). Use either "Force" mode (see
Section 4) or the Blockware's "Manual" mode (if provided) to vary the actuator's position in 5-10% steps (do not use
S/M mode). Then observe the actuator response. If the actuator hunts, increase the Deadband. If the actuator
doesn't hunt, decrease the deadband in increments until it does hunt after a move, and then increase the deadband
until the actuator doesn't hunt. Try to get the Deadband as small as possible WITHOUT hunting occurring.
Stroke Time, Parameter 6 (Positioner mode):
TOUT
uses Parameter 6 in an anticipator calculation to minimize
actuator undershoot and overshoot during each move. This parameter should be set to the approximate time (in
seconds) that it takes to move the actuator from 0% to 100% (Scaled Position). Typically, 85% of the actuator
nameplate stroke time is used. Values above 100% of the actual stroke time can cause overshooting and
subsequent hunting. Values below 45% of the actual stroke time can cause false
TTRIP
trips due to "Slow Moving".
After the Deadband has been adjusted, if the actuator continues to overshoot or undershoots excessively, adjusting
the Stroke Time can help to reduce this. If the actuator undershoots, increase Stroke Time; if the actuator
overshoots, decrease the Stroke Time.
WARNING
The
TOUT
Fault Detection logic may require external Pull-up and Bias resistors for proper
operation. Failure to provide these parts and to test the installed system can result in
EQUIPMENT DAMAGE, INJURY, OR DEATH.
The Fault Detection logic in
TOUT
is NOT sufficient for ALL applications. Each application must
be individually assessed and the control logic and external safety shutdown systems must be
individually designed for the application. Many applications require additional independent
monitoring (for example: A Low Oxygen burner trip).
Actuator Fault Detection (Positioner Mode): Some Hazardous applications monitor the actuators for "faults" to cause
an alarm or safety shutdown. An example is parallel positioning of separate fuel and air actuators for burner fuel-
air ratio control.
TOUT
provides internal fault monitoring logic that is made available to other Blocks via the
TTRIP
and
TCODE
auxiliary Outputs.
This logic is designed for actuators with position feedback potentiometers (pots) that are wired directly to a PCC-IV
analog input. This logic is NOT designed to work with 4-20 mA or other types of position feedback signals. This
logic is designed to detect an open circuit in any of the Pot field wires or the Pot element, stalled or burned out
motors that are not moving, and overloaded motors that are moving very slowly.
Typical actuator faults include: blown actuator power fuses, open field wiring, burned out motor windings, dirty
feedback pots that cause the wiper to go open circuit, and worn feedback pot resistance elements that break and
go open circuit.
The internal
TOUT
Fault Detection logic monitors the actuator. A Fault is indicated by a
TTRIP
Output (0=Normal,
1=Fault), and the type of Fault is indicated by a
TCODE
0-4% analog Output as shown below.
