When To Use Earth; Four-Wire Versus Two-Wire Connections - Fluke 5500A Operator's Manual

5500A
Operator Manual

4-15. When to Use EARTH

The 5500A Calibrator front panel NORMAL LO terminal is isolated from the chassis
(earth) ground. When it is desired to make a connection between the NORMAL LO
terminal and earth ground, press the
default condition is off (annunciator not on).
To avoid ground loops and noise you must have only one ground connection in the
system. Usually you make all signal ground connections at the UUT and verify the
annunciator is off. For the 330 A range and synthesized resistance and capacitance, be
sure the
the UUT is battery operated and completely isolated from earth ground. There must,
however, be a safety ground for the 5500A. See "Connecting to Line Power" in
Chapter 2. When enabled by the sourced output, a softkey LOs appears, which allows
you to tie or open an internal connection between the NORMAL LO terminal and AUX
LO terminal. When tied and
ground.

4-16. Four-Wire versus Two-Wire Connections

Four-wire and two-wire connections refer to methods of connecting the 5500A to the
UUT to cancel out test lead resistance to assure the highest precision of the calibration
output. Figures 4-1 through 4-3 illustrate the connection configurations for resistance;
Figures 4-4 through 4-6 illustrate connection configurations for capacitance. The
external sensing capability of the four- and two-wire compensated connections provides
increased precision for resistance values below 110 k and capacitance values 110 nf
and above. Part of the setting up the calibrator output for resistance and capacitance
includes selections for four-wire compensation (COMP 4-wire), two-wire compensation
(COMP 2-wire) and two-wire no compensation (COMP off). (See "Setting Resistance
Output" and "Setting Capacitance Output" later in this chapter.) Note that compensated
connections for capacitance are to compensate for lead and internal resistances, not for
lead and internal capacitances.
Four-Wire Connection The four-wire connection is typical for calibrating laboratory
measurement equipment. Increased precision is provided for resistance values below
110 k and capacitance values 110 nF and above. For other values, the lead resistances
do not degrade the calibration and the Calibrator changes the compensation to off
(COMP off).
Two-Wire Compensation The two-wire connection is typical for calibrating precision
handheld Digital Multimeters (DMMs) with a two-wire input. Increased precision is
provided for resistance values below 110 k
For other values, the Calibrator changes the compensation to off (COMP off).
Compensation Off Compensation off is a typical connection for calibrating handheld
analog meters or DMMs with a two-wire input. This connection is used for all values of
resistance and capacitance and is usually selected when the analog meter or DMM level
of accuracy does not require the additional precision. This is the default condition
whenever an ohms or capacitance output is made, following an output that was not ohms
or capacitance.
4-10
annunciator is off. Generally,
is on, then both LO terminals are tied to chassis
button, lighting the button annunciator. The
is on only for ac and dc volts where
and capacitance values 110 nf and above.