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G8MNY > TECH 24.07.05 09:24l 101 Lines 4396 Bytes #999 (0) @ WW
BID : 55384_GB7CIP
Read: GUEST OE7FMI
Subj: Mains Peak/RMS/Mean Meter
Path: DB0FHN<DB0RGB<DB0MRW<DB0WUE<DK0WUE<7M3TJZ<F6KMO<HR1FBB<CX2SA<GB7YFS<
GB7CIP
Sent: 050723/1644Z @:GB7CIP.#32.GBR.EU #:55384 [Caterham] $:55384_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (Updated Dec 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 (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!
eg 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 O/P
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.
150K 470K Pot 470K
ÚÄÄÄÄÂÄÄÄÂÄÄ/\/\/\ÄÄÄ\/\/\/ÄÄÄ/\/\/\ÄÄ¿
_³_ _³_ ³ Cal/³\ ³
1w /_\ /_\ ³________ RMS³ MEAN >
AC L ÄÂÄÂÄÄ22ÄÄÄ´ 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. 22ê 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, use higher wattage Rs.
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 or inverter 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 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.
Why don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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