Keithley 3730 User Manual

Section
5: Basic Digital Multimeter (DMM) Operation Series 3700 System Switch/Multimeter
User's Manual
5
-28 Document Number: 3700S-900-01 Rev. A / August 20
07
Basic circuit theory dictates that I
REF
is equal to the I
DUT
. Since the voltmeter of the Series 3700
(V
MEAS
) has very high input impedance (>10G), current through the voltmeter branch is
insignificant and can be discounted. Therefore, as shown in the following Figures Equation 1, I
REF
= I
DUT
Figure 5-17: Two-wire ratiometric method
Since I = V/R, Equation 1 is modified using the V/R equivalents in place of I
REF
and I
DUT
.
Therefore:
I
SOUR
= (V
MEAS
/ R
REF
) + (V
MEAS
/ R
DUT
)
Keep in mind that V
MEAS
is measured by the Series 3700. With V
MEAS
, I
SOUR
, R
REF
known, the Series
3700 calculates the resistance of the DUT and displays the result. R
REF
is learned during
calibration and V
SOUR
is routinely self-calibrated when the dmm.autozero attribute is enabled
(dmm.autozero = dmm.ON).
As shown, the 4W function can also be used to measure ohms for the 10M and 100M
ranges. To minimize the effects of charge injection when dmm-autozero is enabled, the 10M to
100M is actually a 3-wire ohm measurement. SENSE HI is not used. SENSE HI is connected
to the DUT but is not required (it can be left open). The measurement method is similar to the
ratiometric method for 2W, but it performs an extra voltage measurement (V
LEAD
) to
compensate for voltage drop in the input test leads.

Keithley 3730 Specifications

General

Brand	Keithley
Model	3730
Category	Multimeter
Language	English