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Photo-Multiplier tube voltages?

Discussion in 'Electronic Design' started by Jamie, Jan 26, 2013.

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  1. Jamie

    Jamie Guest

    At the lab, there is a smoke chamber and it has a photo tube.

    This is this problem, for what ever reason the lab has 0 documentation
    of the electronics and the service tech they tend to use for calibration
    does not know any more.. All he knows is what it suppose to be at the
    end of the anode with a 1MEg load on it, which is 0..5V ..

    Ok, all that is just fine however, there is some confusion about
    the voltage requirements for this tube, of course, we can't find any
    spec's on that either.

    In any case, after looking at generic photo multiplier tubes and
    circuits it appears that -600DC at the cathode seems to allow this to
    work ok when we calibrate for dark current. We need the tube to have
    some linkage at dark current so when the filter is applied we have a
    detectable view of the smoke.

    Does 600V sound about right?

    The calibration tech seems to think it should be down around -350VDC
    which works fine for a clear view but has a drop off so the filter view
    has very low sensitivity, which makes perfect sense to me since the tube
    needs to be ionized to get some leakage.

    We do have photo multipliers in use elsewhere however, those supplies
    are up around 1kVDC and that we do have proper specs and design work but
    they are a much larger tube, the supply in the smoke chamber unit can
    only output up to -700DC.

    What's your take on this voltage scale?


    Jamie
     
  2. Robert Baer

    Robert Baer Guest

    From Wikipedia, "Photomultiplier tubes typically utilize 1000 to 2000
    volts to accelerate electrons within the chain of dynodes."
    And i can attest to that, as the manager for Oil 4 Less LLC, we sell
    high voltage shunt regulators designed for PMTs in downhole applications.
    The only time we sell 400V regulators is in conjunction with 1250V
    regulators, giving 1650V for the PMT and a voltage tap for one of the
    dynodes.
    Use the Baby Bird (Goo Gull) and look up Hammamatsu PMT specs.
     
  3. Jamie

    Jamie Guest

    Thanks Phil, that just about covers it then.

    We do use 12 stage units at a -1KDC for the detection of the slightest
    arc that could take place inside a vessel that gives us the voltage for
    the 2Mev ebeam.

    As for the tube number in question for the other poster, I don't have
    it at the moment. Memory tells me it was something like 7102 or
    something, but it's a side view detector with 11 pin octal base with all
    pins occupied. That could mean 9 dynodes with cathode and anode, maybe..

    Jamie
     
  4. MrTallyman

    MrTallyman Guest

    Bwuahahahahahah!

    some PMTs those must be.

    Ours, which power the PMTs still in use in the F-4 Phantoms in Japan
    and Israel, were of the 1650V variety, and that went through the whole
    string on the dynode array.

    The big key is keeping the leakage current to less than 3 picoamps.

    The tube socket is the most common culprit, and almost certainly why
    their lame design does not carry ay higher excitation voltage.

    Ours can see a single photon. Like the launch flash of a missile fired
    15 miles behind the plane.
     
  5. Robert Baer

    Robert Baer Guest

    * Lazy...
     
  6. Robert Baer

    Robert Baer Guest

    Please refer to: http://www.oil4lessllc.org/PMT/
    The PMTs.pdf copy is a good reference, as well as the
    PMT_handbook_v3aE.pdf which is by Hammamatsu.
    Both were downloaded from the web.
     
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