Tweco 400 MST Arc Master - Manual (Page 34)

7
VOLTAGE REDUCTION DEVICE (VRD)
7 – 1
Voltage Reduction Device (VRD)
1
VRD Specification
2
VRD Maintenance
Routine inspection and testing (power source)
An inspection of the power source, an insulation
resistance test and an earth resistance test shall
be carried out.
a. For transportable equipment, at least once
every 3 months
b. For fixed equipment, at least once every 12
months.
The owners of the equipment shall keep a suitable
record of the periodic tests.
NOTE
A transportable power source is any equipment
that is not permanently connected and fixed in the
position in which it is operated.
In addition to the above tests and specifically in
relation to the VRD fitted to this machine, the fol-
lowing periodic tests should also be conducted by
an accredited Thermal Arc service agent.
If this equipment is used in a hazardous location or
environments with a high risk of electrocution then
the above tests should be carried out prior to enter-
ing this location.
3
Switching VRD On/Off
Switch the machine Off.
a. Remove the clear plastic cover from the control
panel (see Figure 7-1).
 Lift up the cover so it rests on the top of the
unit.
 Place a small flat bladed screw driver between
the cover hinge on the front panel.
 Gently lift the cover hinge out of the front cover
mounting hole.
 Remove the control's clear plastic cover.
Figure 7-1: VRD ON/OFF Step A
b. Remove four mounting screws from the control
panel (see Figure 7-2).
c. Access the VRD control by gently prying back
the front panel controls to reveal the VRD on/
off potentiometer (see Figure 7-2).
CAUTION
Do not pull back the front panel with excessive
force as this will unplug control PCB. Plugging the
control PCB back into the front panel controls can
only be achieved by removing the side covers.
Figure 7-2: VRD ON/OFF Step B,C
Description
ArcMaster
400MST
Notes
VRD Open
Circuit Voltage 15.3 to
19.8V
Open circuit voltage
between welding
terminals.
VRD Resistanc.
148 to 193
ohms
The required resistance
between welding
terminals to turn ON the
welding power.
VRD Turn OFF
Time 0.2 to 0.3
seconds
The time taken to turn
OFF the welding power
once the welding current
has stopped.
Description IEC 60974-1 Requirements
VRD Open
Circuit Voltage Less than 20V; at Vin=230V or 460V
VRD Turn ON
Resistance Less than 200 ohms
VRD Turn OFF
Time Less than 0.3 seconds
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