Hypertherm PAC500 Water Injection Plasma Cutting System - Manual (Page 46)

WARNING
Before making this check, shut off the disconnect switches to both the control panel and power supply.
PAC500 Instruction Manual 5-5
4
MAINTENANCE
Spark Gap
The spark gap assembly located in the high frequency generator (figure 6, page 5-16), should be inspected every
three months. The electrode spacing should be set at .020 in. If adjustment is necessary, loosen the 5/16 in. lock
nut and 1/8 in. Allen set screw; push the electrode against the feeler gauge and tighten the set screw and lock nut.
Repeat this procedure for the other electrode. The .020 in. setting delivers the maximum energy possible from the
tank circuit. Do not use other settings.
Control Circuit Description
The control schematic for a single torch system is shown in figure 9, page 5-19. The location of the relays denoted
in the control schematic, are shown in Figures 6 and 8. The locations of plumbing components such as solenoid
valves, gas and water flow interlocks, and the water cooled pilot arc resistor are shown in Figure 7. The terminal
strips are designated as follows: 1TB located on relay panel (figure 8), 2TB located on high frequency panel
(figure 6), 3TB located in plumbing compartment (Figure 7), 4TB located in operator’s panel.
When the ON/OFF switch (1SS) is turned ON the POWER ON light (WHITE) glows. The GREEN light indicating
that the power supply contactor is energized will come on after the start command is given (manually with start
button or automatically) if adequate gas and water flow is available.
Test Mode
The TEST mode allows the control to be cycled without the DC power coming on. When placed in the TEST
position, the TEST/RUN switch, line 5, deactivates the TEST/RUN relay (1CR), line 5, so that NO contacts of 1CR
opens both the circuit which controls the power supply contactor (CON), line 13, and the circuit which initiates
machine start, line 26. The High Frequency Generator does not operate in the TEST mode because the contacts of
3CR line 28 are open. If testing of the high frequency circuit is required, a jumper wire may be placed across the
3CR contacts at 1TB-18 and 1TB-19. This will cause the high frequency circuit to operate in the TEST mode. Do
not operate the High Frequency Generator without all of the consumables inserted in the torch as irrepairable torch
damage will occur.
Arc Detection. The control sequence is much easier to follow if the operation of the arc detection circuit is
understood. This circuit is simply a D.C. relay in series with two zener diodes connected across the power supply
output (but physically located in the console). An R.F. Choke is used to protect the diodes from stray high frequency
currents. The zener diodes drop the voltage down to an appropriate value for proper operation of the relay coil.
When the power supply is energized the 400 volt output is more than sufficient to pull in the relay 3CR. When a
main arc is established the power supply voltage drops to somewhere in the range of 125 to 220 volts which is
insufficient for holding the relay in so it drops out. The relay therefore operates in reverse logic manner which may
be confusing to those unfamiliar with the circuit. The normally closed contacts of the relay are open when the arc is