Ammeter Rated Voltage

Discussion in 'General Electronics Chat' started by Electronic 88, May 25, 2015.

  1. Electronic 88

    Thread Starter New Member

    May 25, 2015
    6
    0
    Hello, I've some question regarding the Rated Voltage on Ammeter.

    How can I know what is the Rated Voltage from the existing Ammeter? Do it have a Label? Or we can measure it?

    I've attached the photo of my existing Ammeter.

    Existing.JPG

    Thanks.
     
  2. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
    2,803
    1,237
    The 'maximum working [insulation] EMF' of D'arsonval units should be specified in the manufacturer's literature...

    Best regards
    HP
     
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    If that is a DC ammeter, measure the resistance of the meter. That and Ohm's law gives you the maximum working voltage.

    ak
     
  4. Electronic 88

    Thread Starter New Member

    May 25, 2015
    6
    0
    Thanks for the reply, the meter is already 20 Years old back. Sad that, I can't get anything from the manufacturer.
     
  5. Electronic 88

    Thread Starter New Member

    May 25, 2015
    6
    0
    As I know that DC ammeter should have 2 lines with one of it is doted and parallel to each other. I guess the symbol at the left bottom shows it's DC ammeter, am I right?
     
  6. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
    2,803
    1,237
    That, and the FS current indication, would allow calculation of the full scale deflection 'voltage' drop (IOW the maximum terminal-to-terminal EMF)--- It is my impression, however, that the OP wishes to determine the insulation strength (i.e. the maximum EMF at which the instrument may be safely operated above chassis/environmental ground)...?

    Best regards
    HP
     
    Last edited: May 26, 2015
  7. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
    2,803
    1,237
    Polarity symbols (i.e. "+" and "-") on or near the terminal posts would suggest that the instrument is indeed a DC indicator, however absence of same does not necessary mean otherwise...

    Further assistance will require resolution of the ambiguity illustrated via posts #3 and #6 To wit: by 'rated voltage' do you mean maximum terminal-to ground 'voltage' consistent with safe operation? Or are you merely interested in the 'voltage' drop across the meter at full-scale deflection current?

    Best regards
    HP
     
  8. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    That is typically not a useful parameter, thus it's usually not specified. You should only connect a current to your meter, hopefully a current that's equal to or less than the max reading. Voltage will take care of itself.
     
  9. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
    2,803
    1,237
    While I agree that knowledge of E(full swing) is of little value (save for calculating shunt parameters) -- Insulation 'voltage' is an important consideration in applications 'floating' the meter above Ca. 100v As, for instance, monitoring current drawn from the B+ rail in 'electron tube' equipment, etc...

    Best regards
    HP
     
  10. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    Well, maybe. In that case (floating the meter on B+), the insulation strength you are talking about would be the insulation between the meter's coil structure and the case, since that is the only part that could be in contact with GND. The small meter's I've seen over the years have thick cases, so thick that the float voltage would have to be in the kV range before the dielectric strength of the plastic case became something of concern.

    ak
     
    Hypatia's Protege likes this.
  11. Electronic 88

    Thread Starter New Member

    May 25, 2015
    6
    0
    Here is the diagram at which I'll connect the ammeter in series to the circuit as shown to know the current flow through the "photo sensor" which is use for Flame Monitoring.

    As shown in the diagram, there is "+" and "-" sign, it should be DC Ammeter.

    But instead of the symbol from the circuit diagram, is that the DC/AC can be seen from the Ammeter itself (From left bottom as in Ammeter Picture posted earlier)?

    Actually Supplier ask me to provide them with the following spec.

    Model: (OK)
    Range: 0-600uA (OK)
    Rated Voltage: Just like the question above, is that 220V or 440V will be very much different for ammeter?
    Dimension: 72 x 72mm (OK)

    I also thought it's just ampere passing through the circuit (I mean from the diagram)? Correct me if wrong.

    Thanks.[​IMG]
     
  12. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
    2,803
    1,237

    Unless you will be purchasing/fabricating shunt{s}, the sole significance of 'voltage' is the meter's insulation rating (Spec. maximum allowable potential difference 'metered line' to chassis/ground) - probably not an issue in your application --- The 'voltage' across the meter is determined by the current through, and internal resistance of, same and need not be considered, unless, again, you need to calculate shunt resistance...

    Best regards
    HP
     
  13. Electronic 88

    Thread Starter New Member

    May 25, 2015
    6
    0
    Thanks for the reply,

    If I choose the higher rated voltage eg: 440V Ammeter, is that the 440V ammeter can be use for 220V circuit too? As I think it's the maximum allowable voltage, which suppose to be fine if I use higher rated Ammeter (440V) in the same or lower voltage (440V/220V) circuit right?

    :)
     
  14. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
    2,803
    1,237
    Yes, an ammeter rated at (i.e. insulated to) 440 volts is applicable to lower EMFs -- One caveat though, 220v and 440v are standard 'mains' (and, hence, AC) EMFs -- But your previous posts seem to indicate you require a DC ammeter -- Are you certain the instrument under consideration is applicable to your application?:confused:

    While not impossible, I think it unlikely that DC instruments would be 'specified' at common AC values... Just my $0.02:)

    Best regards
    HP
     
  15. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    AFAICR: there were 2 standard voltages for those meters, you had to check which you had before ordering shunts.
     
  16. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    A quick search on Wiki came up with 75mV and 100mV.
     
  17. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
    2,803
    1,237
    ...As opposed to 220V and 440V which is why I maintain that the specification in question is that of maximum working case insulation EMF:D

    Best regards
    HP
     
  18. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    Seems I overlooked that bit of the original question, somehow I just never seemed to have bothered checking insulation rating of meters, maybe because I rarely operated them on mains potential lines.

    The more modern meters are nearly all plastic with the innards separated by quite some distance from any mountings - they're probably good for 1000V or more.
     
    Hypatia's Protege likes this.
  19. Electronic 88

    Thread Starter New Member

    May 25, 2015
    6
    0
    1. I think the symbol shown in the 1st image is DC Right?
    2. If that is DC ammeter, I think you are right, it should not have such rating on 220V or 440V which is AC right?

    Thanks :)
     
  20. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
    2,803
    1,237
    1) No -- I do not regard a pentagram-bound '3' as indicative of DC operation:confused:;):D -- however, based upon the image attached to post #11, I feel the instrument is, indeed, a DC indicator...:)

    In consideration of the incongruous markings and general 'confusion' -- taken with possible safety issues -- I feel it judicious to withhold 'endorsement' pending clarification (IOW sticking my neck out is one thing, placing same in a (guillotine) lunette is quite another!:eek:)

    On a (hopefully constructive) note please consider these points:

    -Based upon the attached image and schematic you require a 600 MicroAmpere DC (full-swing) movement period!:cool: -- The drop across the meter need not concern you unless the specifications require a shunt (very unlikely for a 600uA movement!).

    -The (insulation) EMF rating is not important if the device will be operated at EMFs no greater than 120v above earth ground (note: the insulation EMF rating is strictly a safety matter, my choice of 120v owes to my considered opinion that all movements will be insulated to at least that value)

    -In general please be advised that scale markings may be inconsistent with specifications in the absence of 'expected' shunts, rectifiers, etc... Hence the advisability of comparison of specified parameters with scale markings (as to, for instance, full-scale current, form [i.e. AC vs DC], linearity, etc.)

    Best regards
    HP
     
    Last edited: Jun 9, 2015
Loading...