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G8MNY  > TECH     09.11.23 08:15z 104 Lines 4480 Bytes #4 (0) @ WW
BID : 59974_GB7CIP
Subj: Mains Peak/RMS/Mean Meter
Sent: 231109/0800Z @:GB7CIP.#32.GBR.EURO #:59974 [Caterham Surrey GBR]

By G8MNY                                               (Updated Dec 04)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

True Root Mean Squared (RMS) meters either use an insensitive moving iron
movement (with a non linear scale) or have active Squarer circuits (digital or
analogue) to compute the value. So most meters are only "Average" (Mean)
indicating & calibrated up to indicate the RMS value, by applying sine waveform
correction factor of 111%.

Real mains is normally 240V RMS in the UK but based on the EU standard of 230V.
Substations are normal set the +10% max on no load.

  Eu        Heating    PSUs    Meters
NOMINAL       RMS      PEAK     MEAN
+10 %  Max    253V     358V     228V
+4.3%  UK     240V     340V     216V
   0%  EU     230V     325V     218V
-4.3%  USA    220V     311V     198V
-10 %  Min    207V     292V     186V

N.B. ñ10% of voltage means a change of 49% of the power rating!
e.g. a 2.3kW fire @ 230V goes from 1.86KW @ 207V to 2.78kW @ 253V.

Most electronic equipment needs the right peak voltage to work properly, & not
as often found on generators & inverters some clipped 240v square wave that has
the same peak as RMS voltage!

340V PK __³     _                     ?? PK _³             GENERATOR or
240V RMS _³   /' `\ Sine Wave      240V RMS _³  _______    INVERTER OUTPUT
218V MEAN-³  ³     ³  MAINS         ?? MEAN /³ ³       ³   With Electronic
          ³ ³       ³                        ³ ³        ³  Rectified Load
       0v_³³_ _ _ _ _³_ _ _ _ _           0v_³³_ _ _ _ _³_ _ _ _ _ 
          ³          ³         ³             ³          ³         ³
          ³           ³       ³              ³           ³        ³
          ³            ³     ³               ³           ³_______³
          ³             \,_,/                ³

This simple passive meter circuit can be used to give a more meaningful
measurement of a Generator/Inverter AC supply, or to upgrade an existing meter.

The added Peak & Mean features can be ignored for simple RMS meter.

                  _³_  _³_  ³         Cal/³\             ³
              1W  /_\  /_\  ³________  RMS³   MEAN      4K7    
  AC  L ÄÂÄÂÄÄ22ÄÄÄ´    ³          PK\o   o   o         Pot<ÄÄÄ¿
        Ne ³       ³    ³                /³\         DC Cal   +³
MAINS N ÄÁÄ)ÄÄÂÄÄÄÄ)ÄÄÄÄ´                 ³              ³   100uA
          Ne Ne   _³_  _³_           47n ===             ³   Meter
EARTH E ÄÄÄÁÄÄÙ   /_\  /_\           500V ³              ³     ³
                   ³    ³                 ³              ³     ³

Box         Old Plug top PSU with 3 metal pins.

Resistors   1/4 Watt or higher if using lower values. 22R is a fuse type.

Diodes      Hi PIV types e.g. 1N4007

Cap         400V or higher Polly type.

Cal Pots    Preset type (N.B. mains is on them if adjusted from outside!)

Switch      Any 3 pole 300VAC (low current) switch. (3 coloured positions)

Meter       100uA Scaled 0-360V, or 50% Back wound movement Scaled 160V-360V.
            Use 3 Colour bands on the scale for ideal readings.
            Mounted so that it is well insulated. (double insulated?)
            For higher current meter e.g. 1mA divide the R values by 10, &
            multiply the Capacitor value by 10, use higher wattage Rs.

Neons       With internal Rs, can be added L-N, L-E, N-E, show status of 
            voltages on the wiring. On Household Mains only L-N & L-E should
            light up, on a floating generator or inverter feed all will be lit.

Warning this means using MAINS VOLTAGES! Use an isolation transformer & variac
if you can, to make it safer!

1/ Apply smooth 250V-300V DC on the AC input, adjust the DC Cal pot for the
   same reading. Or use the Peak reading feature & measure the voltage across
   the Cap with a Digital meter & adjust the DC Cal pot to read the same.
   This simulates a perfect square wave.

2/ Apply 50Hz 240V AC sine wave & adjust Cal RMS pot for the same reading. This
   varies the amount of peak voltage that is added to the mean voltage to get
   the pseudo RMS reading.

3/ Check that with 240V AC the meter reads 340V Peak & 218V Mean.

See my bul "Meter Movement Types".

Why don't U send an interesting bul?

73 de John G8MNY @ GB7CIP

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