Transformer Primary Current Monitoring |
(See Schematics Here) |
Shown Above: Correct High Voltage Transformer Phasing: capacitor voltage hits -1700 volts as transformer output is going negative. Capacitor charge appears briefly more negative than transformer output.
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Shown Above: the compensated high voltage divider lead is connected to the high voltage rectifier input. A current Transformer monitors Applicator Coil current.
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Incorrect Transformer Phasing, same measurement shown above (with primary leads swapped)Shown Above: Incorrect High Voltage Transformer Phasing
Screen centerline represents zero volts. Vertical scale is 1000 volts per division. Sweep is triggered by the primary SCR firing. We get a glimpse of zero volts. Then we see -1700 volts (driven by resonant action): transformer output tracks that. Positive transformer output drives capacitor droop upward until the Ringback SCR fires, clamping voltage to zero again briefly. Resonant action ends with the Cap charged to +1500 volts. Then transformer output continues to recharge the capacitor positively. Transformer output eventually goes negative again, rather abruptly due to slow reverse recovery-time of the high voltage diode. |
Ross 1000:1 Compensated High Voltage Divider |
Peak Capacitor VoltagePeak Capacitor Voltage Measurement
Shown Above: Capacitor voltage rises higher and higher over the course of four successive power-line cycles, then the primary SCR dumps that charge into the Applicator Coil. |
To measure peak capacitor voltage, the lead from the compensated divider is connected to the high voltage rectifier output (as shown above). The current transformer remains positioned to monitor Applicator Coil peak current.
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Applicator Coil Voltage |
Applicator Coil Drive Current |
Shown above: the Primary SCR shorts the positive side of the capacitor to ground; the negative side of the capacitor drives the Applicator Coil. (The charged Capacitor is switched in parallel with the Applicator Coil.) The center line on the screen represents zero volts, scale is 500 volts per division: -2000 volts energizes the Applicator Coil. Field strength peaks as the capacitor reaches full discharge. Collapsing field then reverses capacitor polarity, charging it to about +1700 volts. SCRs used here have slow reverse recovery time, so some charge is lost back to the Applicator Coil. SCR reverse current switches OFF abruptly. Minor Applicator Coil field collapse produces a -500 volt spike (damped by a Resistor-Capacitor snubbing network of 20 Ohms and .45 microfarads).
Biphasic Pulse Current |
Peak current scale is 200 Amps per division, showing about 1240 Amps peak. My calibration is out of date, so these readings are only estimates.
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Peak SCR Hold-Off Voltage (Continued)Above we see peak positive SCR hold-off voltage reaching about 2000 volts. (Ringback SCRs are connected antiparallel to the Primary SCRs, so this also represents reverse hold-off voltage for them.)
Test Data Sheet |
Series SCR Midpoint VoltageAbove we see midpoint voltage between the two SCRs. Amplitude tracks at about half of Peak SCR Hold-Off Voltage (seen in the prior two photos). This confirms voltage is being split evenly across both series connected SCRs.
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