Tweco SC11 - Manual (Page 28)

OPERATION 4-4 Manual 0-2556
C. AUTO HT Indicator OFF and FIND HT
Indicator ON
NOTE
The standoff height is not controlled during the
cut except manually by the operator using the
TORCH UP/DN switches.
1. The cutting machine controller sends a start signal to
the Standoff Control.
2. The Standoff Control starts to find height by rapidly
lowering the torch from the retracted position towards
the work. When the torch contacts the work or the
bottom of torch travel if not over the work, it opens
the normally closed (NC) torch on work (T.O.W.)
switch in the Lifter Motor Assembly.
3. When the T.O.W. switch opens the torch downward
motion is reversed and it slowly rises until the T.O.W.
switch closes which starts the PIERCE HT timer. The
torch continues upward for the time required to reach
the selected pierce height setting.
4. A start signal is sent to the Plasma Power Supply and
the Standoff Control PLASMA ON indicator turns
ON. The pilot starts after pre-flow and immediately,
if the initial height is correct, the cutting arc is estab-
lished at which time the Plasma Power Supply sends
a motion (OK-To-Move) signal to the Standoff Con-
trol.
5. Receiving the motion (OK-To-Move) signal from the
Plasma Power Supply starts the PIERCE DELAY. As
the PIERCE DELAY ends the motion (OK-To-Move)
signal is sent to the cutting machine controller, start-
ing the horizontal travel.
NOTE
Torch height is not controlled automatically.
6. The piece is cut then the cutting machine removes the
start signal. The arc goes out removing the Motion
(OK-To-Move) signal from the Plasma Power Supply.
7. When both the start and motion (OK-To-Move) sig-
nals are removed (allows for current ramp down for
systems that have that feature) the retract timer is ac-
tivated to rapidly raise the torch up to clear obstruc-
tions, such as cut out pieces that tilt up, while travers-
ing to the next piece to be cut. The amount of retract
is set from zero to 100% by the END OF CUT RE-
TRACT Control. The torch remains retracted until the
sequence repeats with the next start signal.
D. Fully Manual Mode (AUTO HT and FIND HT
Indicators OFF)
NOTE
Initial height is set manually and controlled manu-
ally during cutting. PIERCE DELAY is still ac-
tive and the arc volts display indicates actual arc
volts but the ARC VOLTS control will not change
the standoff.
1. The cutting machine controller sends a start signal to
the Standoff Control.
2. A start signal is sent to the Plasma Power Supply and
the Standoff Control PLASMA ON indicator turns
ON. The pilot starts after pre-flow and immediately,
if the initial height is correct, the cutting arc is estab-
lished at which time the Plasma Power Supply sends
a motion (OK-To-Move) signal to the Standoff Con-
trol.
3. Receiving the motion (OK-To-Move) signal from the
Plasma Power Supply starts the PIERCE DELAY. As
the PIERCE DELAY ends the motion (OK-To-Move)
signal is sent to the cutting machine controller, start-
ing the horizontal travel.
4. The piece is cut then the cutting machine removes the
start signal. The arc goes out removing the Motion
(OK-To-Move) signal from the Plasma Power Supply.
E. Starting Off The Plate (Workpiece)
When starting off the plate (running edge start) FIND HT
indicator should be OFF and height set manually. AUTO
HT indicator is normally ON to control height after the
cut starts.
When starting off the plate there is no start motion (OK-
To-Move) signal as there has been no arc transfer. For
systems with normally open PSR contacts, Merlin 3000
for example, wiring the contacts in parallel with the mo-
tion (OK-To-Move) signal contacts supplies the motion
start signal as soon as the pilot starts. Use the PIERCE
DELAY to supply time for the torch to move over the
workpiece before the Standoff Control starts controlling
the height.
For systems where the output voltage drops below 195
volts during piloting, SW1 turned ON, will start motion
when the pilot starts (refer to Section 3.08, Internal Selec-
tions). Use PIERCE DELAY to allow time for arc transfer
before the Standoff Control starts controlling height.
For those systems where neither of the above applies then
some external means of detecting pilot (PSR) will have to
be added and connected to the motion (OK-To-Move) sig-
nal contacts as explained above.