Help with meter panel

Discussion in 'The Projects Forum' started by andersonmilltexas, Mar 17, 2013.

  1. andersonmilltexas

    Thread Starter New Member

    Mar 17, 2013
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    Greetings,

    Newbie--

    I am building a meter panel for my generator. One of the meters is a Hertz meter. I bought on ebay it is an AC analog SCI meter from the 1970's
    See pictures.
    The gauge range is 55 to 65 Hz. When I connect to a known steady Hz of 60, the meter pegs itself to the right.

    I see soldered on the back a 6K resistor. This could of been an add on from previous owner???

    Any suggestions?
    Thank you
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Can you provide the make and model number or a link to the datasheet?
     
  3. andersonmilltexas

    Thread Starter New Member

    Mar 17, 2013
    23
    0
    Sorry,

    I do not have a data sheet. It is made by a division of GE. A company called SCI.

    The following numbers are on a label on the back
    50-255350anan2jah
    rtg 0-120 v
    03/0/012/0060/817

    A white hand stamp with the number 030

    Thank you
     
  4. andersonmilltexas

    Thread Starter New Member

    Mar 17, 2013
    23
    0
    My mutil meter shows 11k Ohms between the two posts. How do I determine if this needs a transducer and if so what size
     
  5. MrChips

    Moderator

    Oct 2, 2009
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    I have searched for information on 60Hz frequency meters but have not found any relevant information. It would appear that all such meters are center zero meters and they require a special circuit or transducer to function properly in this application. Some meters appear to have the transducer built-in. Maybe someone else can shed some light.

    Oops. I just noticed your meter is not center zero. That makes it even more puzzling.
     
  6. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    I doubt that is it s "Hz meter" at all! I think it may just be an ammeter. Try a small DC current through it (from a variable voltage DC supply through a resistor) and see if it is just a moving coil meter where the reading increases as DC current increases.

    Failing that it will be a moving iron meter which is just an AC ammeter.

    The most likely scenario is that it had an external support circuit to make it read in Hz.
     
  7. andersonmilltexas

    Thread Starter New Member

    Mar 17, 2013
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    Well I opened it up and found the circuit board. It appears it is a direct connect. I do not see a crystal and it is to old for a micro controller. I also do not understand the purpose of the two large pots.

    What is your opinion? Do you think this is a direct ac connection?
    It is stamped on the back 0-120 volts will the 122 volts I used deflect the meter to the peg??

    Or am I all wrong on this?
     
  8. MrChips

    Moderator

    Oct 2, 2009
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    I was more interested in how such a meter would work. There has to be some kind of phase comparison circuit with a 60Hz reference. It would be great if someone has a link to the circuit used in such units.

    If we can reverse engineer your circuit we should be able to find the problem. I see some transistors on that board. I would imagine the pots are for calibration purposes.
     
  9. andersonmilltexas

    Thread Starter New Member

    Mar 17, 2013
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    Could this circuit be a Wein Bridge?

    The transistors would not make sense though??????
     
  10. debe

    Well-Known Member

    Sep 21, 2010
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    184
    Most likely a analogue freq meter (tacho type circ). Try using it on a lower voltage as it may need a resistor to lower the voltage, 0-120Vac is a fairly big range. Another type such as on my Honda generator has 5 viabrating reeds that indicate 45/50/55/60/65Hz & runs of a 6V ac winding on the generator.
     
    Last edited: Mar 19, 2013
  11. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Yep, Debe is right, it's a standard old "tacho" type freq meter. They use two transistors (top) as a monostable, and the whole thing needs a regulated voltage (normally a zener diode). So one monostable pulse is made per incoming freq pulse, and it just feeds the average voltage output to a DC voltmeter. (Average voltage output is directly proportional to freq.)

    The meter itself is definitely a moving coil voltmeter type, which also matches the "tacho" design.

    To get it working you need to find the zener diode and check the voltage, as it needs enough input voltage to make the zener regulate. From the look of that big 5W resistor externally mounted on the back they might have just connected it to 120v AC. What value is that resistor?
     
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