Tweco SC11 - Manual (Page 31)

Manual 0-2556 5-3 CUSTOMER/OPERATOR SERVICE
2. Faulty Arc voltage input to Standoff Control
a. Check for proper arc voltage input per Section
5.05-G, repair as necessary
J. Torch dives or oscillates while cutting instead of
maintaining constant height
1. Lifter speed set too high
a. For travel speeds under150 inches per minute
select low speed
2. Faulty motor tachometer
a. Check the motor/tachometer per Section 5.05-
H, repair as necessary
5.05 Test Procedures
This section describes the tests required to isolate prob-
lems or faulty assemblies in the Standoff Control Assem-
bly. The section contains a functional description of the
Standoff Control followed by individual test procedures.
Each procedure is referenced in Section 5.04, Trouble-
shooting Specific Problems.
A. Functional description
The Standoff Control controls the operation of the torch
lifter motor assembly to find height, regulate height and
retract at the end of cut per the following sequence:
1. Standoff Control receives a START signal.
2. Torch moves down at high speed until the torch
tip contacts the workpiece.
3. Torch retracts at slow speed to the setting selected
by the PIERCE HT control.
4. Upon finding height as set by the PIERCE HT con-
trol a START signal is sent to the plasma power
supply and the PLASMA ON indicator turns ON.
5. The power supply starts the arc which pierces the
metal.
6. After the time delay as set at the PIERCE DELAY
ends, a motion (OK-To-Move) signal is sent to the
cutting machine to start the cutting motion.
7. As the cutting machine accelerates the standoff
inhibit (corner slowdown - CSD) signal is re-
moved.
8. The THC ACTIVE indicator turns ON and the
Standoff Control regulates height to maintain the
selected standoff.
9. At times during the cutting operation the
controllor program may disable the Standoff Con-
trol by applying the standoff inhibit (corner slow-
down - CSD) signal. When this occurs all three
decimals in the ARC VOLTS display turn ON and
the THC ACTIVE indicator will turn OFF.
10. At the end of the cut program the START signal is
removed.
11. The torch retracts at high speed to the setting of
the END OF CUT RETRACT (%) control . This
setting is a percentage (%) of the full lifter travel.
If the FIND HT indicator is OFF, the system will
skip the find height sequence and the retract at
the end of the cut. The desired pierce height is set
manually.
If the AUTO HT indicator is OFF, height is not
controlled during the cut.
The Torch Lifter Assembly uses a dc motor with a tachom-
eter for speed and direction feedback. The motor pinion
gear mates with a rack on the up/down slide to move
the torch. A second small vertical slide allows about 1/2
inch of free movement. Held down by the weight of the
torch it keeps the Tip-On-Work micro-switch (mounted
above the small slide) closed. When finding height, as
the torch moves downward and makes contact with the
the work, the small slide moves up, opening the micro-
switch to signal that the torch has made contact with the
work.
B. Front Panel Switch Tests
The four switches have a common connection to J3-
13. To check the operation of the switch measure for
continuity from the PC Board common (TP1) to the
other side of the switch at J3 per the following:
S w it c h J 3 P in #
M O D E 8
L I F T E R S P E E D 1 2
T O R C H U P 1 7
T O R C H D O W N 1 4