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G8MNY > TECH 13.04.04 19:02l 83 Lines 3816 Bytes #999 (0) @ WW
BID : 52666_GB7CIP
Read: DB0FHN DL3NDX GUEST OE7FMI
Subj: Mains Peak/RMS/Mean Meter
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Sent: 040413/0858Z @:GB7CIP.#32.GBR.EU #:52666 [Caterham] $:52666_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (New Apr 04)
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 to compute
the value. So most meters are only "Average" (Mean) indicating & calibrated to
indicate the RMS value, by applying sine waveform correction factor of 110%.
Real mains is normally 240v RMS (EU 230v, +10%=253v Max) & has a peak value of
340v (357v Max) with a mean value of 218v. Most electronic equipment needs the
right peak voltage to work properly, & not some clipped 240v square wave that
has the same RMS voltage!
340v PK __³ __ ?? PK _³ GENERATOR or
240v RMS _³ / \ Sine Wave 240V RMS _³ ______ INVERTER O/P
218 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.
150K 470K Pot 470K
ÚÄÄÄÄÂÄÄÄÂÄÄ/\/\/\ÄÄÄ\/\/\/ÄÄÄ/\/\/\ÄÄ¿
_³_ _³_ ³ Cal/³\ ³
/_\ /_\ ³________ RMS³ MEAN >
AC L ÄÂÄÂÄ100ÄÄÄ´ ³ PK\o o o 4K7 ><ÄÄÄÄ¿
Ne ³ ³ ³ /³\ Pot > +³
MAINS N ÄÁÄ)ÄÄÂÄÄÄÄ)ÄÄÄÄ´ ³ DC Cal> 100uA
Ne Ne _³_ _³_ 47n === ³ Meter
EARTH E ÄÄÄÁÄÄÙ /_\ /_\ 400v 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. 100ê is a fuse type.
Diodes Hi PIV types eg. 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 eg 1mA divide the R values by 10, &
multiply the Capacitor value by 10.
Neons With internal Rs, can be added L-N, L-E, N-E, show the status of
the voltages on the wiring. On Household Mains only L-N & L-E
should light up, on a floating generator feed all will light up.
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 with 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.
/QSL
73 de John G8MNY @ GB7CIP
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