Active Collimator Interface Specification

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The collimator provides 8 outputs that are dependent on current and position. The outputs have the following characteristics, listed below. Lead shielded local amplification is necessary within 1 m of the device in order to limit bandwidth truncation due to the extra input capacitance of the coaxial cable. Digital electronics are to be located elsewhere, in a VME crate mounted in an electronics rack in Hall D proper. The x,y position coordinates are computed from the 8 measured currents through an algorithm to be provided by the UConn group.

System Requirements

  1. Position measurements
    • 500 pA to 5 μA electron beam
    • 200 μm RMS resolution on photon beam centroid at collimator entrance
    • bandwidth is 1 kHz above 50 nA, and I(electron beam)/50nA in kHz below 50 nA
  2. Feedback control
    • bandwidth 1 kHz
    • latency less than 150 μs
  3. 8 preamplifiers
    • dc gain dynamically selectable in 6 discrete ranges: 1012, 1011, 1010, 109, 108, 107, 106 V/A
    • exact dc gain depends on termination load used on output
    • nominal values above are stated by manufacturer for 100 Ohm load
    • plans are to use 75 Ohm output cable (RG-59/U or equivalent)
    • coordinates computed from diff/sum ratios, independent of gain scale
    • bipolar output signals with range [-10, 10] V
    • preamp bandwidth: varies with gain range, compute using gain-bandwidth product
    • all 6 ranges have the same gain-bandwidth product: 1013 Hz * V/A
    • bandwidth in any gain setting obtained as (gain-bandwidth product) / (dc gain)
  4. 8 analog outputs from the active collimator readout board
    • x+ coarse, x- coarse, x+ fine, x- fine, y+ coarse, y- coarse, y+ fine, y- fine
    • differential outputs (four signals, each in +/- pairs)
    • each output is unipolar from 0 to 2 V
    • output circuits have >1 kHz bandwidth
    • coarse outputs gain: 100 mV difference / cm
    • fine outputs gain: 10 V difference / cm
  5. 2 analog magnet control outputs
    • single ended (?)
    • unipolar from 0 to ? V (?)
    •  ? kHz bandwidth
    •  ? resolution
  6. Digital I/O
    • Beam Sync input for pulsed mode
    • 30 Hz input for line sync of waveforms
    • 4(?) BPM inputs (just to be safe?)
      • 0.5 nA to 5 μA electron beam
      •  ? kHz bandwidth
    • Other and/or spare I/O ?
  7. EPICS control
    • remote gain control for preamps, independent 3-bit values for 8 channels
    • coarse and fine position read backs at 1 Hz for Ops
    • waveform buffers
      • adjustable up to 4k points at 4ksps, triggered by 30Hz or Beam Sync for Ops
      • circular buffers for FSD captures for Ops
  8. Physics analog outputs for Hall D data acquisition system
    • 8 buffered analog outputs providing raw collimator sector currents
    • 8 analog outputs for processed signals (x+/x- coarse and fine, y+/y- coarse and fine)
    • signals will be digitized and recorded using standard GlueX data acquisition
  9. Physics digital data outputs
    • none
  10. 4 diagnostic analog outputs (?)
    • single ended (?)
    • bipolar +/- V (?)
    •  ? kHz bandwidth
    •  ? resolution
  11. 2 diagnostic analog inputs (?)
    • single ended (?)
    • bipolar +/- V (?)
    •  ? kHz bandwidth
    •  ? resolution
  12. Account code?