Duff-Norton SK6420-6 - Manual (Page 6)

SECTION III
OPERATION
ii. Being careful not to turn the pot shaft, slide
it into engagement with the plastic worm and
tighten locknut.
iii. Re-check resistance. If necessary loosen
locknut slightly and twist pot to re-establish
100 ohm resistance. Pot does not have end
of travel stops, but has a 20˚ deadband
between the two ends of the resistive element.
No continuity will be measured to terminal S
S
if the slider is in the deadband.
iv. Run actuator to full extension (do not let
tube rotate) until it is stopped by its limit
switch.
v. Check resistance between S S and C CC CW W to
be sure the slider is still on the element and
the resistance is greater than 100 ohms. The
pot has enough rotation for 9.43 inches of
travel. (For strokes shorter than 9”, the
retracted resistance can be increased so that
pot adjustment is less critical.
b. FOR TRAVELS GREATER THAN 9 ” ”
(MULTI-TURN POT):
i. Turn pot shaft counterclockwise until it
reaches its stop. Now turn shaft back
clockwise 1 / 4 turn.
ii. Without turning pot shaft, slide pot onto
engagement with the plastic worm and tighten
locknut.
iii. Starting 1 / 4 turn from the end, the 3-turn
pot has enough rotation for 25” of actuator
travel.
6. With this set-up, potentiometer will have increasing
resistance from S to CCW (and decreasing resistance
from S to CW) as the actuator extends.
2-5. DIGITAL POSITION INDICATOR (DUFF-NORTON PART
NO. SK6300-4K)
The model SK6300-4K is a highly versatile, panel mount,
digital readout device that provides a very precise
indication of actuator position. It can be programmed to
display percentage, inches, or any other desired unit.
The indicator is self calibrating with no need for
measurements or calculations.
See detailed instructions with the SK6300-4K
indicator for installation and programming instructions.
Potentiometer terminal C CC CW W should be connected to
indicator Common, C CW W to Excitation Voltage, and S S to
Signal Voltage Input.
3-1. OPERATIONAL PROCEDURES
This motor is an intermittent duty type motor. Since the
motor draws approximately the same amperage at no
load as at full rated load, it only takes 10 minutes of
cntinuous running, regardless of how light the load may
be, before the thermal overload relay cuts out. It then
takes about 10 minutes before the motor cools
sufficiently for the thermal relay to close. Make sure that
the duty cycle to which the actuator is subjected is not
too severe for the motor.
Avoid using low voltage supply for the motor. All
wiring, switches etc. must be of sufficient capacity to
carry the required current.
The axis of the clevis pins should be parallel so
that the actuator can pivot without binding. A few drops
of oil should be used on the clevis pins.
The preset brake will provide consistent braking
for the actuator. However, in the event the brake friction
surfaces become worn as indicated by excessive drift,
the brake will require rebuilding. To aid in rebuilding, a
repair kit with step by step instructions is available
through Duff-Norton Company under repair kit part
number SK-6415-41. The repair can be performed by
the customer or by any authorized repair station.
WARNING
This actuator is not recommended for use in applications
where it can be jammed. Examples of jamming include
overtraveling the limit switches and thus jamming the nut
and screw internally at the extreme ends of the stroke,
and driving the actuator against an immovable object
and thus severely overloading it. This actuator can jam a
limited number of times without damage. Therefore,
consult Duff-Norton Engineering if jamming is expected.
Do not operate actuator before setting limit
switches.
Some actuator external surface temperatures
may reach 230˚F at or near maximum allowable duty
cycle.
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DN-SK6420-6-1006 10/10/06 11:40 AM Page 6