Making Measurements - Sinclair PDM 35 Owner's Manual

MAKING MEASUREMENTS
=
DC voltage:
Four ranges are available each with an input
impedance of IO Mn. On the XI range a small
zero offset may occur from minute leakage
currents. This will disappear when the leads
are shorted together and will not affect the
reading once a voltage is connected.
If a- sign appears in the display the voltage is
negative with respect to the common lead.
CAUTION - do not apply more than 1000
volts.
AC Voltage
AC voltage is only available on the X Iooo V
range. The input impedance is 450Kn.
The meter senses the mean value of an input
and is calibrated to read the R.M.S. value of a
sine wave. Any DC
=
on the input in
addition to the AC
l f )
will affect the reading.
CAUTION - do not apply more than 500
volts R.M.S.
=DeCurrent
6 ranges are available each with a voltage drop
of Im V per count. Ail ranges are available via
the mA-n socket and the multiplier for each
fLA range is written in the grey blocks above
the DCV ranges.
A leakage current of up to ±InA may be
present in the meter which would cause an
error on the xO.rnA range. The offset must be
added to or subtracted from the reading.
CAUTION- a current is measured by making
it flow through the meter (by breaking the
6
l
1
)
J
circuit and re-connecting it via the test leads).
Connecting the current function directly across
a voltage source could result in permanent
damage.
NOTE - AC current cannot be measured
directly with this instrument.
Resistance
5
ranges of resistance are available each
generating a voltage across the unknown resis-
tor of
+
Im V per count relative to the common
lead. If the resistor is in place across a semi-
conductor junction, it may be necessary to
reverse the leads to avoid forward biasing the
junction.
CAUTION - Ail power must be removed
from a circuit before trying to measure
resistances.
Testing of Semi-conductor Junctions
The instrument measures resistance by forcing
a known constant current through the resistor
and measuring the voltage developed. The re-
sistance ranges can be used to measure the
forward voltage drop of semi-conductor
junctions, and to match VBEs of transistors etc.
The current used on each range is as given in
the grey blocks at the top of the range
information, and the reading on the display
is the forward voltage drop in volts. The
mA-n socket is the positive terminal of the
current source.
Overload
With the exception of the x IoooV DC
=
and ACV) ranges, ail ranges can be used up to
7