ELOG DESPEC

AIDA GELINA BRIKEN nToF CRIB ISOLDE CIRCE nTOFCapture DESPEC DTAS EDI_PSA 179Ta CARME StellarModelling DCF K40

DESPEC

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Entry time:

Thu Oct 6 16:51:49 2022

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Investigating AIDA noise with a TA041 differential probe and oscilloscope

AC Mains (DESPEC platform AC, L-N)
Probe attentuation = 1:100

Fig 1: Main AC waveform [X: 5ms/div, Y: 100 V/div]
Fig 2: Zoomed in at peak (20 V FSR, any less and the waveform clipped) [X: 10us/div, Y: 20V/div]
Fig 3: Longer time base and FFT of 0-5 MHz. No significant frequency harmonics noticed [X: 5ms/div, Y:20 V, FFT X: 500 kHz/div, Y: 10 dBm/div]

No significant noise or distortion present, fully within any AC specification. 
Note that at the moment there is almost no load on AC
Equipment on on DESPEC rack: AIDA NIM, AIDA Raspberry Pis, bPlas PC (+ WR) + 2x DESPEC NIM crates
 No autofill, VME crate or detectors
All big machines at GSI (SIS, FRS) off (suspect pumps are on)

Ion catcher not on (I think under repair)

FEE PSU studies
Probe connected to 5V exposed power pin on FEE64 (+v) and to grounding crimp on FEE64 (-v)
No adapter board connected
Attentuation = 1:10

Fig 4: FFT when FEEs are *off* - essentially probe+scope noise [X: 5ms/div, Y: 100 mV/div, FFT: X: 500 kHz/div, Y: 10 dBm/div]
Fig 5: FFT when FEEs are *on* - notice 1.4 MHz peak in FFT, also seen on ADC waveform readout before (fig 6) [X: 5ms/div, Y: 100 mV/div, FFT: X: 500 kHz/div, Y: 10 dBm/div]

Fig 7: 500 ns/div 5V output on FEE, single FEE on the PSU [X: 500 ns/div, Y: 100 mV/div]

Note average max voltage is 5.31 V (power on) and ~ 70 mV "peak to peak" -might be from probe/scope?

Also see voltage changes with FEE power draw:

Power on  : 5.45 V (different scale to above)
SETUP ran : 5.51 V 
FADCs off : 5.86 V
ACQ Go:   : Unchanged; ASIC threshold 0xa: Unchanged

Also check situation on a fully loaded PSU (8 fees connected and powered on)

Power on:   5.29 V (fig 8)
SETUP ran:  5.36 V (fig 9)
FADCs off:  5.64 V (fig 10)

All X: 500 ns/div, Y: 100 mV/div

Both cases observe voltage rises as current draw drops (as expected for voltage drop along a cable)

Noise on 'scope seems to get slightly worse with reduced current (and higher voltage)

No sign of strong 100 kHz noise as seen in ADC traces beforehand

Todo:

- Check -6V and 7V rails
- Check 5V and noise when front-end card is added and pulser/HV connected
- Check between two FEE64 grounds 
- Check direct out of PSU vs ground to see if 1.4 MHz appears on PSU side or FEE64 side

-
11.10.22 Updates

Attachement 11 - 5V PSU on upper PSU with no FEEs attached whatsoever. No 1.4 MHz (on FFT) but clear low frequency beats from switching - presumably low/no load behaviour

Attachement 12 - 5V PSU on aida12 with 8 FEEs on PSU. Longer time base to allow lower frequencies in FFT. 1.4 MHz switching spikes visible but nothing around 100 kHz region

Attachments 13-16: 5V PSU on aida12 at 20 mV/div vertical and 1, 0.5, 2, 5 us/div horizontal respectively

12.10.22 Updates

Attachment 17: -6V PSU on aida12 with 8 FEEs on PSU. 2 us/div timebase. 20 mV/div amplitude
Attachment 18: 10 ms timebase and FFT
Average voltage: -6.21 V

Attachment 19: 7V PSU on aida12 with 8 FEEs on PSU. 2 us/div timebase. 20 mV/div amplitude
Attachment 18: 10 ms timebase and FFT
Average voltage: 7.46V

Measurement between AIDA12 ground and Reference ground/copper bar
+ve (red probe) attached to copper bar at ground point (not strong connection at present)
-ve (black probe) attached to ground crimp on aida12 (connected to cooling plate)
aida12 no adapter board connected: connections are PSU, Ethernet, HDMI and TTY only

Attachment 21: 5 us/div 100 mv/div waveform, big oscillations present. Not seen before FEEs turned on (8 FEES, 1-7+12)
Attachment 22: 10 ms/div for FFT, sharp peak at exactly 100 kHz observed...

Attachment 23: Between 5V PSU (+ve) and 19" rack (-ve) with  no FEEs connected to PSU
 See strong 100 kHz oscillations too, note that voltage isn't 5V as PSU is floating w.r.t. ground
 Looks to be common mode noise (on both 5V and Return of PSU)

Attachment 24: Same as 21 but using thick crocodile clips on probe to ground and aida12. Noise is attenuated but still present

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