Log entry time 21:08:37 on November 03, 2009

Entry number 297295

This entry is a followup to: 297039

Figure 1 shows the lousy MPS signal we get from the counting house at the Moller DAQs down in the Hall. Note that the timescale is 4 us/division, so it's not really apparent if you're looking at the full 500us wide MPS interval.

Figure 2 shows the relative timing between signals as they enter the Moller DAQ after the MPS has been "reconstituted" by running it through a GDG as described in an earlier halog.

  QRT:  Pink
  HEL:  Yellow: Lags QRT by ~20--140ns depending on + --> -, or + --> -
transition
                Bright yellow, faint yellow show the two Hel transitions
  MPS:  Blue:   Lags the QRT/HEL by ~300ns

Figure 3 is a shot of a 'scope upstairs in the counting house. The upper trace (1) is HEL, and the lower trace is MPS -- both come directly from the fibre to NIM converter units. Note that the MPS v. HEL timing here is quite different than in Fig 2. These signals agree with the injector settings and have the MPS lagging the HEL transition by 1us.

I traced the signals from the MPS/HEL fibre translator boards into a real mess of fanned out copies generated from LeCroy linear fans and a P726 ECL-NIM converter (which is used as a logic fan-out more than a level convertor). It's a real rat's nest there and I didn't want to risk messing anything up so I did not dig into it. When it eventually comes out, the MPS signal has been delayed by something on the order of a microsecond relative to the HEL signal (no picture, sorry). There are a couple of GDG modules in the mix -- I presume one of them gets involved.

We also noted that it is the LeCroy linear FI/FO in the second last slot that is generating the noise on the MPS signal running to the Moller DAQs. It's also clear that someone noticed this problem in the past and reconstituted one copy of the signal through a GDG three slots to the left (Figure 4). I didn't trace the output from the GDG so I'm not sure if it goes to the HRS DAQs, the Compton, or what. The finger in the photo points to the GDG unit, the black unit to the left is the ECL-NIM used as a convoluted FO, the LC429A to the right is generating noisy signals.

The cabling here is a real mess and should be complete redone from scratch. We'll leave sleeping dogs lie for now since we don't want to screw anything up (situation is essentially the same as it was for the last experiment), but a rework should probably be put on the PREx 'todo' list... It would be a good idea to put a fan on the NIM bin too -- it's packed full.

A copy of this log entry has been emailed to: gen@jlab.org, brads@jlab.org, glamazdi@jlab.org, rom@jlab.org

Figure 1: Lousy MPS coming from CH at the Moller DAQ in the Hall

Figure 2: MPS, QRT, HEL leading edge timing at the original Moller DAQ

Figure 3: MPS/HEL timing at the the fibre convertor boards in the CH

Figure 4: NIM bin in CH middle room showing rat's nest, bad Logic FIFO (2nd slot from right), and the GDG that fixes the MPS for someone else's system