Panel Meters.

Discussion in 'General Electronics Chat' started by PackratKing, Oct 7, 2008.

  1. PackratKing

    Thread Starter Well-Known Member

    Jul 13, 2008
    Looking for info: Humor an old fart..............:p

    the motivation here, is to find out if an analog panel meter, culled from a stereo multiplex, formerly the "VU" meter, would serve the purpose, for a 0 - 20, max 30 [ with adequate shunting ] ac ammeter, or are these strictly dc units, making it necessary to rectify \ filter the ac to get an acceptable indication.

    Most deceased multiplexes I run across, amplifier chips are crispycritters, because owner did not pay attention to impedance when hooking in extra oversize spkrs, so the vu meters should still be relatively virgin ???

    I have a good supply of expendable components to build support circuitry with, but would rather not burn things up unnecessarily.
  2. beenthere

    Retired Moderator

    Apr 20, 2004
  3. studiot

    AAC Fanatic!

    Nov 9, 2007
    Many equipment meters were decidely nonlinear when used to indicate a particular function.

    Audio VU meters, and power meters
    Radio 'S' meters, tuning indicators and VSWR meters

    fall into this category.

  4. AlexR

    Well-Known Member

    Jan 16, 2008
    Its the scale that is non-linear on VU, S etc meters. You will find that the meter movements themselves are in fact linear.
    True VU meters have a lower damping factor than normal panel meters but I don't think it will make a lot of difference in this application. In any case I doubt that the meters in consumer audio equipment are true VU meters.
  5. PackratKing

    Thread Starter Well-Known Member

    Jul 13, 2008
    No problemo, StudioT.............That's how we learn, by experimentation and asking questions ! I am determined to fart around with the theory, and if I discover anything noteworthy, I shall share it here.

    I've often heard it said that the only stupid question is the one you don't ask..........

    Beenthere.........The ones I have prepped so far, I just turned the printed plate over, and painted it, then installed calibrations culled from comparisons to a known meter, such as my Fluke 77.

    As the sage once said.......some things [ vu meters ] are " close enough for government work ! " :D
    Last edited: Oct 7, 2008
  6. sam2008

    New Member

    Oct 7, 2008
    Panel meters are used to display an input signal, and measure current, voltage, and frequency. They are equipped with bright LED displays for display only or set point control options. Many panel meters also include alarm options as well as the ability to connect and transfer data to a computer.
    Last edited by a moderator: Oct 8, 2008
  7. studiot

    AAC Fanatic!

    Nov 9, 2007
    Sorry but life is a deal more complicated than this.

    Some providers of non linear scales use external circuitry to control an off-the-shelf standard linear meter. This is especially true of prototypes and small production runs.
    The BBC has a specification for just such an VU meter.

    However certain meter types are inherently non linear eg moving iron types. Others with moving coils are manufactured with a non linear response by shaping the field magnets and/or adding internal components. This technique is common in volume production of small meters found in audio amplifiers, CB sets etc etc.

    Turning the scale plate is a good wheeze, but be careful how you remove and replace it as it is all too easy to damage the needle or suspension.
    Most meters have an angular range between zero and FSD of from just under 90 degrees to about 110 degrees. With the plate off it is easy to measure this so you can work out the new scale points on linear meters.