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G8MNY > TECH 22.02.26 18:08l 143 Lines 6864 Bytes #7 (0) @ WW
BID : 52818_GB7CIP
Subj: Lafayete 57 Range Multimeter
Path: JH4XSY<IW0QNL<SR1BSZ<EA2RCF<CX2SA<GB7CIP
Sent: 260222/0906Z @:GB7CIP.#32.GBR.EURO #:52818 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Corrections Jan 16)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Model 99-5076
ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
ｳｳ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ｳｳ DC Volts 0.25 2.5 10 50 250 1000 @ 25K/V
ｳｳ ｳｳ 0.125 1.25 5 25 125 500 @ 50K/V
ｳｳﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿｳｳ
ｳｳｳｳ~~~~~~~~~~~~~~~~~~~~~~~~~~~ｳｳｳｳ DC Amps 50uA 5mA 50mA 500mA 10A @ Normal
ｳｳｳｳ ｳｳｳｳ 25uA 2,5mA 25mA 240mA 5A @ 2x
ｳﾆｵｳ . ｳﾆｵｳ
ﾀﾙｳｳ '. ｳｳﾀﾙ AC Volts 3 10 50 250 1000 @ 2.5K/V
ﾚｿｳｳ '. . ｳｳﾚｿ 1.5 5 25 125 500 @ 5K/V
ｳｳｳｳ '. :'\': ｳｳｳｳ
ｳﾆｵｳ '. '�.�' ｳﾆｵｳ 10x dB scales & DC isolated AC.
ｳｳｳﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙｳｳｳ
ﾀﾙｳﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄｳﾀﾙ Ohms ｫFSD 13R 65R 650R 6K5 65K
ｳ o- +o ｳ (|) ｳ o o ｳ
ｳ ｳ ｳ ｳ Accurancy DC 2%, AC 3%
ｳ [ｱ ]rev ｳ_________ｳ ｫ[ ｱ] ｳ
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ
MULTI METER PRINCIPLES
DC VOLTS 1000 100 10 1 Volts
To get a meter of just one ﾚ10Mﾄﾂﾄ1Mﾄﾂ100Kﾂﾄﾄﾄ11K1ﾄﾄﾄﾄ>+
sensitivity to do many o o o o
ranges voltage multiplier /ｳ\
resistors are used. Here +ｳ
the voltage drop across /~~~\
the meter is ignored, but ｳMeterｳ
it will affect the lowest 90uA\___/
1V scale. ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ>-
Series resistors are used
to protect the switch more Sensitivity is 11K1/V
from high voltages.
DC CURRENT 100uA 1mA 10mA 100mA
For current ranges shunts +ﾚﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ>+
are put across the meter. /~~~\ \ｳ/
Here the meter resistance ｳMeterｳ o o o o
is 100R so it has 10mV drop 100uA\___/ ｳ ｳ ｳ
@ 100uA. The 1mA shunt here 10mV ｳ 11R 1R 0R1
is corrected for the 100R ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾁﾄﾄﾄﾄﾁﾄﾄ>-
meter load.
AC VOLTS
For AC a rectifier diode is
used, and normally this alters 1000 100 10 Volts
the sensitivity, so a different ﾚ4M5ﾂﾄ450Kﾂﾄﾄﾄﾄ45Kﾄﾄﾄﾄ>~
multiplier arm from the DC is used. o o o
In this circuit only half the /ｳ\
current goes through the meter +ﾚﾄﾄﾄｴ<ﾃﾄﾄｴ
and the 1.1 AC sine wave form /~~~\ D1 _ｳ_D2
factor means that 2.2x meter ｳMeterｳ /_\
current must flow. Only a 100uA\___/ ｳ100uA
100mV is lost in the germanium ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ>~
diode D1, so the low voltage
range can take this into account
on the scale. D2 can be any type Sensitivity is 4K5/V.
and protects the low voltage D1.
OHMS
Here a voltage source is put
in series with the meter and a
known resistance that set the
half scale resistance and includes (actually -ve!)
the meter load resistance. ﾚﾄﾄCal Zero Rﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄ>+
The higher the battery +ｳ \ｳ/
voltage the higher resistance /~~~\ o o o o
that can be measured, but ｳMeterｳ ﾚ10ﾁ100ﾁ1Kﾁ10Kﾙ
becomes a danger for 100uA\___/ ｳ
sensitive electronics. ｳ ｳ ｳ+
The Cal zero R sets the meter ﾀﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾛﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ>-
sensitive to give full scale ｳ (actually +ve!)
ZERO reading on shorting the
probes depending the battery state.
Note that the battery internal resistance is added to the unknown resistance,
and this affects the low range scale calibration! Also the probe polarity is
reversed to that indicated and it is different than for digital meters!
ACTUAL MULTIMETER CIRCUIT
ﾚﾄ===========================================================================
ｳ I
ｳﾚ========================= =============== ================ =========== =ｿ
\/ ﾀﾄ20Kﾄﾄ80Kﾄｿ ｳ ｳ ｳ
/\ /ｳ\ ｳ ｳ ｳCom + 10A O/Pｳ
ｳﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ ｳ ｳ ｳ ｳ o o o o ｳ
ｳ ____ ﾚﾄｿ ｳ ﾚﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾂﾄﾄ)ﾄﾄﾄﾄﾄ)ﾄﾄｴ ｳu1ｳ ｳ ｳ
ｳ /15uA\ ｳ ICal ｳ ｳ 13 ｳ Low ｳ 13K ﾚﾄ)ﾄﾄ)ﾄﾄﾁｴﾃ)ﾄﾄﾙ ｳ
ｳ ﾚｴ Meterﾃｴ ﾃﾄﾄﾄﾄﾄﾄﾄ)ﾄ)ﾄｿ ｳ 46K ﾚ4K7ﾂｴ<ﾃｴ ｳ ｳ ｳ ｳ ｳ ｳ
ｳ ｳ \____/ ｳ12K5 ｳ ｳ ｳ ｳ ｳ oNorｳ 3K3 ｳ ｳ ｳ ﾀ0R025ｴ ｳ
ｳ ｳ ｳ ｳ o o ｳ ｳ ｳﾚ> ｳ ｳ ｳ ｳ ｳ ｳ ｳ
ｳ ﾃﾄﾄｴ>ﾃﾄﾄﾄｴ ﾀoNor ﾚ> X <ﾙ ｳ ｳｳ oｫ ｳ 5kHiｳ ｳ ｳ ｳ ｳ
ｳ ﾃﾄｴ<ﾃﾄﾄﾄﾄｴ <ﾄﾄﾄｴ o o ｳ ｳｳ ﾀ4K7ﾁｴ>ﾃﾁﾄﾄﾙ ｳ ｳ 0R475 ｳ
ｳ ﾃﾄﾄVCalﾄﾄﾙ ﾚoVA/2ｳRev Nor ｳ ｳｳ Low ｳ ｳ ｳ ｳ
ｳ ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄ6K25ﾙ ﾚ)ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ))ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｴ ﾀﾄﾄﾄﾄﾄﾄﾄﾄ)ｿ ｳ
ｳ ｳｳ ｳｳ ｳ ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾙｳ ｳ
ﾀﾄﾂ56K25ﾂ197K5ﾂ1Mﾂ5Mﾂ18M75ｿｳﾃ47ﾂ650ﾂ6K54ｿﾚｴｳﾚ1M87ﾂM5ﾂM1ﾂ17K5ｴ ﾃ4R53ﾂ45R3ﾅ24K9ｴ
o o o o o oｳo o o oｳoｳo o o o oｴ o o o o
ｳ I ｳ ｳ ｳ
=========================ﾙ=============ﾙ ﾀ================ﾃﾄ================
I ｳ
===============ｿ____ｳﾜｳﾜ________ｳ
+ｳﾟｳﾟ
0.25 2.5 10 50 250 1k R/5 R 10 100 1k 1k 250 50 10 3 500 50 5 50u
\________DC_VOLTS_________/ \_____OHMS____/ \___AC_VOLTS___/ \____DC_mA____/
& dB Scales
The configuration switching between modes and all the ranges is all done on
just 1 large rotary switch with 3 bridging contacts (I) and 5 wipers of 2
circuits.
Only 4 probe sockets are used, 2 extra for the high current (10A) & the DC
isolated AC measurement.
Extra switches provide a meter reverse feature and a double sensitivity that
doubles the number of meter ranges. (has no meaning on ohms!)
This meter's movement is a extremely sensitive @ 15uA for FSD, but not very
accurate, so it is calibrated with an ICal & VCal presets at manufacture.
The AC ranges are calibrated with select on test resistors 2x "4K7 Low" & the
"5K Hi" that accurately allows for the diode forward resistance loss & leakage.
Most of the resistors are special values made for the meter, and of course they
are very accurate and stable 0.5% types.
See my tech buls on "Meter Movement Types", "Maplin Mains Meter 2000MU-UK",
"Edgcume Peebles Megger & Low R", "Edgcume Peebles Earth Loop Z", "Car Dwell
Angle & RPM Meter", & "Kelvin Varley Voltage Divider".
Why don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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