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The Adventures of Sparky LeCroy

The Adventures of Sparky LeCroy

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The Adventures of Sparky LeCroy

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  1. The Adventures ofSparky LeCroy TK Hemmick for the Stony Brook Crew and Maxim

  2. LeCroy Trip Circuit Questions • PHENIX has long suffered from “myths” about the true functionality of the trip circuit in the LeCroy HV PS. • We used the schematic to put the current signal on a digital scope trace. • Triggering on single shot of the scope, we could look at the precise waveform of the current under many conditions.

  3. Spying on the Signals • Pins 1 & 10 of a particular Op Amp carry the “Fast” and “Slow” current signals for a channel (8 OpAmps 8 channels) • Unfortunately these carry a lot of common mode noise as compared to our scope and a DC offset for small current surges.

  4. Dual Sum & Invert • Fast & Slow wires from 2 channels. • Dual Sum & Invert makes clean signal /w adjustable DC offset.

  5. Calibration • Current reported by LeCroy via “VT100” interface. • DC voltage measured by O-scope. • Good Linearity: we know what V means

  6. Fast vs Slow • “Sparking” resistor chain with NO CAPACITORS (other than cables etc…) • NOTE: Slow circuit = Fast output through 10 msec RC and voltage follower. • Ring Amp a little smaller in slow circuit Slow Fast

  7. What do you trip on? • By “brushing” the shorting wire, we can make MANY transients atop the signal. • The Transients DO NOT(!!) make a trip No Trip Here Trips Here

  8. It is a discharge? • Yup…created visible, aubible spark with a wire shorting a big HV cap. • Trips on 1st ring. • NEVER trips with thresh above 1st ring. NOTE: Change in scale by 10X

  9. Best simulation circuit • Big RC (GEM) in parallel w/ small RC (strip) • Spark the strip with a wire • Smaller overshoot • Trip point basically at new DC level.

  10. Summary • Very little difference between “fast” and “slow” trip circuits (“Peak” is misnomer). • Transients never cause trip. • Real circuit has little overshoot (rest of GEM supplies most of charge for sparked strip). • Tripping on extra current due to one shorted strip IS CORRECT!