OUT-OF-CIRCUIT:
(1)
Setthe
FUNCTION
switch
tothe
HIGH
f2position.
(2)
Setthe
RANGE
switchtothedesiredposition.
(3)
Ifthe
resistance
valuebeingmeasured
exceeds
thevalueofthe
range
selected,theoverrange
circuitry
isenergizedand
will
flash.Selecta
higherrange.
IN-CIRCUIT:
(1)
The
Model
283hasselectableLOWand
HIGH
ohms
ranges.
Conventional
resistance
measurements
canbeperformedonall
ranges.
TheLOWohmspositions
limit
themaximum
test
voltagedeveloped
across
themeasured
resistance
to0.2
volt
with
a
full
scale
reading.
This
lowvoltagepermits
accurate
measurements
of
in-circuit
re-
sistances
shuntedbysemiconductorjunctions.
Theapplied
test
voltageisproportionaltothe
resistance
reading
observed,varying
from
zero
with
the
test
leads
shortedto.2
volt
fora
full
scale
reading.Forexample,inthe100f2
range
with
a
resistance
readingof50.0ohms,thevoltagedeveloped
across
the
resistance
under
test
is.05
volt.
When
usingthe
HIGH
ohmspositions,a full-scalevoltageof2 voltsis
developed
across
themeasured
resistance.
Again,
thevoltagede-
veloped
across
themeasured
resistance
isproportionaltothe
resistance
readingobserved.Reversingthe
leads
will
resultinthe
same
reading
(within
1%)ifthereisnoshuntingbya semiconductor,andis
agoodquickcheckthattheaccuracyofthemeasurementisnotbeing
affected
bysemiconductors.
OUT-OF-CIRCUIT
SEMICONDUCTOR
TESTS:
In
additiontoconventional
resistance
measurements,
the
HIGH
ohms
ranges
canbeusedto
verify
thata semiconductor
junction
isgoodby
checking
thefront-to-backratio.
(1)
SelecttheIkf2range.
(2)
Removedevice
from
circuit.
(3)
Connectthe
test
leads
tothedevice(e.g.:diode,base-emitteror
base-coUectorjunction)andthen
reverse
theleadconnections.
Observethemeterreadingforbothconditions.
14
TEST
RESULT
CONDITION
(a)Overrange,bothpolarities
Junction
Open
(b)
ZeroorLowReading,both
polarities
Junction
Shorted
(c)
Overrangeinonedirectionand
In-RangeReadingintheother
Junction
Probably
Good
(4)
Thein-rangereadingof
Step
(c)canbeusedtodeterminewhetherthe
deviceunder
test
is
silicon
orgermanium.A readingof400to700
indicatesthedeviceis
silicon.
Anindicationof100to300indicates
thedeviceisgermanium.
(5)
The
"I-V"
curveofthedevicemaybedrawnusingthe
accurate
current
sources
ofthe283.
With
the
FUNCTION
switchsetto
HIGH
S2,
notethereadingfor
each
positionofthe
RANGE
switch,
lkf2
through
lOMfl.
Disregardingthedecimalpointlocation,
each
readingisnumericallythevoltageinmV
across
thedevice
junction
with
thecurrentthroughitlistedas
Maximum
TestCurrentin
specificationssection.
DC
CURRENT
MEASUREMENTS
a.
Place
the
FUNCTION
switchintheDCAposition.
b.
Place
the
RANGE
switchinthedesiredcurrent
range
position.Alwaysset
the
RANGE
switchtothe1000mApositionifthemagnitudeofcurrentto
bemeasuredisnotknown.
c.Connecttheplus(+)
test
leadtothecurrent
("mA")
test
leadjack.
CAUTION
Use
care
inmakingcurrent
measurements.
Make
sure
thatthemeterisconnected
in-series
with
the
loadsin
which
thecurrentistobemeasured.Never
connectthemeter
across
a voltage
source
with
the
FUNCTION
switchsetforcurrent.
Doing
somay
either
blow
theoverloadprotectionfuseor
damage
theequipmentunder
test.
When
connectingthemultimetertoreadcurrent,
first
removepowerto
the
circuit.
The
following
rules
will
insurethatthepropercurrentpolarity
is
indicated.
15
