The Adventures of Sparky LeCroy TK Hemmick for the Stony Brook Crew and Maxim

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.

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.

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

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

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 Fast Slow

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 Trips Here No Trip Here

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

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.

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!