Operator`s manual

Figure 4-3. The I- and I+ sense leads should be closest to the body of the resistor when making 4WΩ
measurements.
4.3.3 Using Offset Ohms function (SM2064)
Inadvertent parasitic leakage currents, Thermo-voltaic voltages and other sources of voltage errors in a circuit can
be the cause of inaccuracies in resistance measurements. This is common particularly when making measurements
f active circuit. Many users, unaware of the above issues, select very poor switching systems prone to high
-Wire measurements. Offset
v rc s ries, ow se al 2-Wire or 4-
Awire Ohms DMMSetOffsetOhms()
f Wh U d interv e twice negati sitive polarity voltages can be
corrected as long as the total voltage incl resistan ement voltage plus the parasitic voltage are less
than 0.5V. To calculate this voltage consult the specification part of this ma
O ge. ul this fun ALSE. ion is i ented only with the SM2064.
4 re rded R tance urem SM2064)
T 64 a 6-wire r e measur ethod. It to make resistance
m est has other shunting paths, which
ethod isolates the resistor-under-test by maintaining a guard voltage at a user-defined node. The guard voltage
prev
in
ent
shunting most of the DMM Ohms source current. By sensing the voltage at the top of the 30 kΩ, and then applying
this same voltage to the junction of the 510 Ω and 220 Ω, there is no current flow through the shunting path. With
this “guarding”, the SM2064 accurately measures the 30 kΩ resistor.
o
Thermal Errors that introduces some very high offset voltages, be it in 2-Wire or 4
O ll ome error. En lso easure internal resistance of low value hms can a
oltage sou
eviate s
es such a
of this
various batte
abling it can a
low voltage p
s to the enabled or disabled state using the
be used to m
er supplies and nsors. Use the norm
connection, and set the Offset Ohm
Runction. en set T E, the rea al will b
uding the
as set. Both
ce measur
ve and po
nual for the specific current for each
hms ran The defa t value of ction is F This funct mplem
4.3. 6-wi Gua esis Meas ent (
he SM20 provides guarded esistanc ement m is used
easurements when the resistor-under-t can cause inaccurate readings. This
m
ents the shunting of the DMM Ohms source current from the resistor-under-test to other components. The
Guard Source and Guard Sense terminals are provided at pins 1 and 6 of the DIN connector respectively.
Warning! The DIN connector pins are only protected to a maximum of 35 V with respect to the PC chassis
or any other DMM terminal. Do not apply any voltages greater than 35 V to the DIN connector pins.
Violating this limit may result in personal injury and/or permanent damage to the DMM.
Example: Assume a 30 kΩ resistor is in parallel with two resistors, a 510 Ω and a 220 Ω, which are connected
series with each other. In a normal resistance measurement, the 510 Ω and 220 Ω would “swamp” the measurem
Signametrics 36