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Rubidium Lamp Voltage

Discussion in 'Electronic Equipment' started by Joe McElvenney, Apr 29, 2005.

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  1. Hi,

    Rubidium frequency standards based on the EFRATOM FRK modules
    usually have the facility to measure 'Lamp Voltage'. Does anyone
    know what is actually being measured here as the lamp is an
    acorn-sized phial of gas with no internal electrodes? Lamp
    excitation is, I believe, by induction so maybe this 'voltage' is
    simply an analogue of some other process.


    Thanks.

    Joe - Possessor of an aging RACAL-DANA 9475.
     
  2. Dan Rae

    Dan Rae Guest

    It is the voltage of the output of the op-amp that amplifies the output
    of the photocell that is being measured there. Approx 5 to 12V is
    healthy, if 3 Volts, you need a new lamp.

    good luck...
    79 MHz RF
    dr
     
  3. Clarence_A

    Clarence_A Guest

    Lamps are not free nor can they be installed other than in the
    factory.

    If there is Lamp voltage and your not getting lock, there is an
    oscillator adjustment which you might try. Use only a
    non-metallic adjustment tool and try tuning the pot a quarter turn
    "counter Clockwise at a time. Wait a few seconds to see if you
    get lock. then try again. If there is no lock by the time you get
    to max, you can try "Clockwise" slowly, however If you reach less
    than two turns to the end of travel the oscillator is DEAD.

    Efratom was purchased by Datum, six years later it was sold to
    Symetricon. They might still service it, but it is EXPENSIVE!
    These oscillators were about %5,000 to $7,500 in small quantities
    new!
    Test-Equity some times has some refurbished to sell.

    Dan, do you agree? Carolyn gave me the instructions!
     
  4. Hi,

    Thanks to the both of you for that information. In fact the
    standard I have that contains the FRK-L is in good working order
    and locks fine after a few minutes even though the lamp voltage
    is down to 5.5. It is just that on the schematic, the EFRATOM
    subassembly for the RACAL-DANA 9475 is shown as a simple block
    and so far I haven't been able to run down a copy of the internal
    circuit.

    I have a spare surplus lamp arriving in a few days although
    I've had to take it on trust that it doesn't have too many hours
    on the clock. Unfortunately the mounting boss is slightly
    different to mine but I hope to release the bulb from this and
    get a new fitting turned-up. I am able to carry out basic
    confidence checks against off-air standards and, as my
    requirements are modest, the odd digit reduction in the 'n' of
    'parts in 10^n' is not of concern.

    As penance for my sins in a former life, I once had charge of
    a calibration lab where the frequency sources were Rubidium
    referenced. They were dumped when the cost of new lamps or trips
    back to the manufacturer from the Middle-East became greater than
    new GPS-disciplined oscillators.


    Thanks - Joe
     
  5. Clarence_A

    Clarence_A Guest


    There were no schematics released! You will be unlikely to find
    one. I only saw schematics because I quoted the upgrade of the
    FRK, but there was no contract. I had to return the one schematic
    I had, and Carolyn said it was an earlier version anyway. Carolyn
    was the one who assembled and tested the units for compliance for
    eleven years.
     
    Andre Conundrum likes this.
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