Keithley 6514 User Manual

2-8 Measurement Concepts
Guarded connections
The basic guarded connections for volts and ohms are shown in Figure 2-5. For these mea-
surements, circuit high is connected to the center conductor of the input connector while circuit
low is connected to the COMMON banana jack terminal. With guard (GRD) on, the driven
guard is available at the inner shell of the triax connector which is connected to the metal guard
plate.
WARNING The guard voltage is at the same potential as the input. Therefore, hazard-
ous voltage on the input will also be present on the guard plate. To prevent
electric shock, always use a metal safety shield (as shown in Figure 2-5) for
guarded voltage measurements above 30Vrms (42V peak). The metal safety
shield must be connected to safety earth ground using #18 AWG or larger
wire.
WARNING With an open input, up to 250V peak may be present on the guard terminals
while in Volts or Ohms. To prevent this, enable zero check whenever the
input is open.
The driven guard is used to eliminate leakage current and capacitance in high impedance cir-
cuits which could corrupt the volts or ohms measurement. The concept of guarding techniques
are covered in Section 3.
HI
HI
LO
LO
INPUT
250V PK
INPUT
250V PK
COMMON
COMMON
V
Metal Guard Plate
Metal Guard Plate
Metal Safety Shield
Safety
Earth
Ground
Measure Volts
Measure Ohms
Chassis
Ground
GRD
GRD
Ω
NOTE: GRD must be on.
Safety
Earth
Ground
Chassis
Ground
Metal Safety Shield
Figure 2-5
Basic connections
for guarded
measurements

Keithley 6514 Specifications

General

Brand	Keithley
Model	6514
Category	Measuring Instruments
Language	English