Directed Energy, Inc.

            First troubleshooting steps for PVX-41xx pulsers

            If the pulser is a PVX-4140 or PVX-4150 and the problem is no output, first check to see that the interlock is satisfied. The interlock input is pin 1 of the Remote Interface DA-15 connector. This pin must be grounded to for the pulser to operate.

            Because many problems are load- or cable-related, further troubleshooting begins with disconnecting the coaxial cable at the pulser output.

            NEVER disconnect the output cable or the load while a pulser is operating! Doing so can present a shock hazard to personnel and cause arcing and damage to the load and pulser.

            Connect a high voltage DC probe to the output. Feed a logic high level (+5 V) into the GATE input; the output should be at the same voltage as the +VIN power supply.  Change the level at the GATE input to a logic low level (0 V); the output should be at the same voltage as the ­­­­‑VIN power supply.

            If the pulser passes this test, measure the pulse directly at the output connector with an oscilloscope and appropriate high voltage probe. With the cable and load disconnected, any associated HV leaks (corona, micro-arcs, etc.) should be gone and a rectangular pulse should be seen at the output. If not, the pulser needs repair. But if the pulse looks good with no load connected, the load and/or the coax cable is suspect. A simple way to find out is to substitute another load and/or cable. A good clue is provided by the pulser’s overcurrent LED, if present: the LED may blink if an arc or HV breakdown occurs in the coax cable or load. An old coaxial cable is often the source of the problem.

            If the pulse appears distorted, check to see if the applied high voltage exceeds the pulser’s specified maximum input voltage. If so, overvoltage protection devices inside the pulser can conduct and distort the waveform.

            Overcurrent can occur if the load capacitance is excessive -- and that includes capacitance from a very long coaxial cable. Try reducing the cable length or placing a resistor in series with the load. The latter will slow the pulse rise time but will also reduce the peak current.

            Another issue that may come into play is ringing in the waveform, which is caused by inductance. We may not expect to find ringing problems in high-voltage pulsers with their low average currents. But with peak currents of 10 A, 20 A, or 30 A flowing during pulse edges, it is very possible to see ringing on the leading and trailing edges. This can often be fixed by making sure that all of the current is being carried to the load and back again by only the coaxial cable. That is, the load does not have any leakage paths to ground.

            Sometimes the observed ringing is simply the result of scope probes picking up the magnetic fields created by nearby pulse current-carrying wires. Move the probes around to see if the waveform changes.

            Updated: 22 Feb 2019 01:58 AM
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