Four-Wire Versus Two-Wire Connections; Four-Wire Connection; Two-Wire Compensation; Compensation Off - Fluke 5502A Operator's Manual

The Calibrator front panel NORMAL LO terminal is typically isolated from earth
(chassis) ground. When it is necessary to make a connection from the NORMAL LO
terminal and earth ground, push the  key, this lights the key annunciator. When the
earth key is pushed, the NORMAL LO terminal is connected to earth ground through
approximately 30 Ω.
To prevent ground loops and noise you must have only one earth ground-to-LO terminal
connection in the system. Typically you make all signal ground connections at the UUT
and make sure that the  annunciator is off. In most cases,  is on only for ac and
dc volts where the UUT is isolated from earth ground. There must be a safety ground for
the Calibrator. See "Connect to Line Power" in Chapter 2. When the sourced output is
live, a softkey LO is shown, which lets you tie or open an internal connection from the
NORMAL LO terminal to the AUX LO terminal. When tied and  is on, then both
LO terminals are tied to chassis ground.

Four-Wire versus Two-Wire Connections

Four-wire and two-wire connections are methods to connect the Calibrator to the UUT to
cancel out test lead resistance to make sure the highest precision of the calibration output.
Figures 4-2 through 4-4 show the connection configurations for resistance. Figures 4-5
and 4-6 show connection configurations for capacitance. The external-sensing function of
the four- and two-wire compensated connections gives increased precision for resistance
values less than 110 kΩ and capacitance values 110 nF and above. A part of the
Calibrator output setup 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 "Set Resistance Output" and "Set Capacitance Output"
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 calibration of laboratory measurement equipment.
Increased precision is supplied for resistance values less than 110 kΩ. 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 calibration of precision handheld Digital
Multimeters (DMMs) with a two-wire input. Increased precision is supplied for resistance
values less than 110 kΩ and capacitance values 110 nF and above. For other values, the
Calibrator changes the compensation to off (COMP off).

Compensation Off

Compensation off is a typical connection for calibration of handheld analog meters or
DMMs with a two-wire input. This connection is used for all values of resistance and
capacitance and is typically selected when more precision is not necessary for the analog
meter or DMM level of accuracy. This is the default condition when an ohms or
capacitance output is made after an output that was not ohms or capacitance.
Front-Panel Operation
Connect the Calibrator to a UUT
4
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