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G8MNY  > TECH     21.02.19 08:15l 104 Lines 4480 Bytes #8 (0) @ WW
BID : 59862_GB7CIP
Subj: Mains Peak/RMS/Mean Meter
Path: ED1ZAC<ED1ZAC<IZ3LSV<IR2UBX<SR1BSZ<SV1CMG<ON0AR<GB7CIP
Sent: 190221/0705Z @:GB7CIP.#32.GBR.EURO #:59862 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

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

PSEUDO RMS VOLTMETER
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.

                                        470k
                   ÚÄÄÄÄÂÄÄÄÂÄÄ150kÄÄÄÄÄÄPotÄÄÄÄÄ470kÄÄÄÄ¿
                  _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
                   ÀÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÙ

PARTS:-
Box         Old Plug top PSU with 3 metal pins.

Resistors   1/4 Watt or higher if using lower values. 22ê 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.

CALIBRATION:-
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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