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Somebody knows the RFL/Clarke HESS 828 Calibrator?

Discussion in 'Electronic Equipment' started by max, May 5, 2007.

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  1. max

    max Guest


    is it normal that in a 828 RFL/Clarke HEss calibrator if i set
    140mV(as example) at the output i have a tension that is instable :
    140.20 to 139.80 all time? What can be?

    In the range of 10 volt and 100 Volt the things are better?

  2. john jardine

    john jardine Guest

    Marvellous bit of kit!.

    Over a 1 minute period I saw 139.88mV to 140.19mV. This ties in with what
    you see. Even by itself, +/- 0.1% is not bad for the 3.5 digit setting
    But ... the noise is not from the RFL but due to low level AC and RF pickup
    on the leads from the RFL to the DVM.
    A filter of say 1kohm and 1000uF across the DVM input and (my) display is
    rock solid at 140.02mV for minutes on end.

    Got a 828 manual you could share?.
  3. maxi

    maxi Guest


    Yes i've manual that i've download from the site of Clarke Hess.If you want
    i can email to you.
    The problem is that if i set 100 mV,all time my DMM read a instable value
    that oscillate continuosly from 100 to 99.5 to 101 to 99.3 etc.
    In the other range the last digits are more stable.
    I've tried to put the filter acrossss the input of dmm but nothing the value
    is always oscillating,in a second it's change 3,4,5 times!!!!
  4. john jardine

    john jardine Guest

    Yes. I'd be very pleased if you could email it!. My address is ...
    john.jardine [@ sign]

    Sounds like the voltage 828 control loop itself is a bit unstable. Maybe a
    capacitor failing.
    My unit has some internal noise that is coming in from the 240Vac power
    inlet (LO-GND connecting link 'on' or 'off' it's still the same) but not
    the amount you are noticing.

    PS: Just confirming my filter was wired as this ...

    .---------. .---------.
    | CLARKE | | DMM |
    | HESS | | |
    | | | |
    | | ___ | |
    | POS o-----|___|--o----o POS |
    | | 1k | | |
    | | ---+ | |
    | | --- | |
    | | 1000u| | |
    | NEG o------------o----o NEG |
    '---------' '---------'
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