Calorimetry Readout Meeting
June 4, 1998
Steve Hahn
ADMEM Noise Tests with Electronic Loads
- Noise tests using Wiener (switcher/linear regulator hybrid) power supply
- Pleasant surprise: Electronic loads in parallel with power lugs on backplane of VME crate added no detectable noise to ADMEM measurements at any load. Originally thought these used transistor switchers, but schematics show they are just transistors at less than unity gain.
- Could apply 100% load of central ADMEM crate on all power supplies except +15 V where we could only reach 80% @ 10 A
- Interesting surprise: pedestal RMS remained at 3 counts as long as no extra load was put on the -15 V power supply, even if all other supplies were at 100% (except for +15 V at 80%). Load on -15 V power supply is only 1.72 A at 100% (6 ADMEMs), but pedestal RMS rose to 10 counts. At 2.6 A, pedestal RMS rose to 15 counts, and
(RMS difference) vs. delay time shows typical time structure.
- Interesting surprise #2: Looking at AC signal across -15 V power lugs on VME crate with all power supplies at 100% load (but +15), we see 240 mV P-P noise! Main frequency is about 300 kHz, presumably the switching frequency, but there are many frequency components as usual. Watching AC signal as electronic load is turned on and off, these is no discernable difference at any time scale.
- Charlie's plot shows sensitivity to noise in 100 kHz - 1 MHz range for even 1 mV noise at inputs to Café card. Presumably, these is much filtering on ADMEM before Café card inputs, but perhaps not enough on -15 V inputs?
- Noise tests using Condor (linear) power supplies
- Could apply 100% load of central ADMEM crate on all power supplies
- Behavior of Condor linears was same as Wiener switchers, but slightly better. At 100% load on all power supplies (1.72 A on -15 V), pedestal RMS was 8 counts instead of 10.
- Also, tried swapping +15 and -15 V electronic loads just to make sure load itself was not source of noise. It was not.
- Plans for immediate future
- New problem: no thin-wire Ethernet. Hopefully fixed today.
- See if external filtering of -15 V power supply helps
- Should look to see if there is connection between this problem and added cable/capacitance problem (i.e., as function of load)
- Need to understand why Willis and Howard see smaller RMS with Frank's readout code than with Wei Hao (or is it just using external trigger on TESTCLK?)
ADMEM Noise Tests with Electronic Loads / FNAL /hahn@fnal.gov