Keithley 6430 User Manual

Source-Measure Concepts 5-25
The guard test lead IR drop is compensated for by connecting GUARD SENSE as shown in
Figure 5-14B. Sensing allows the guard voltage to be sensed (measured) at the resistor network
for better guard voltage regulation. If the remotely sensed guard voltage is less than the output
voltage of the SourceMeter, the guard voltage will be increased until the sensed guard voltage
equals the output HI voltage.
Note that in order to ensure that ohms guard current (I
G
) in Figure 5-14 does not exceed
50mA, output voltage from the SourceMeter must not exceed 5V (50mA × 100Ω = 5V).
NOTE For 6-wire ohms guard measurements, configure the output-off state to the GUARD
mode. For details on the GUARD output-off state, see Section 12, “Output
configuration.”
6430
x1
I-Source
V-Meter
In/Out LO
In/Out HI
REMOTE
PreAmp
V,Ω GUARD
(Ohms Guard)
Guard
Ohms Guard Selected
I
G
I
L
HI (In/Out)
Guard (Cable)
LO (In/Out)
R
TL
Test Lead Resistance
1Ω
10kΩ
100kΩ
20kΩ
20kΩ
10kΩ
100kΩ
I
G
I
L
R
TL
1Ω
V,Ω GUARD
(Ohms Guard)
HI (In/Out)
Guard (Cable)
LO (In/Out)
6430
x1
I-Source V-Meter
In/Out LO
In/Out HI
REMOTE
PreAmp
Guard
Ohms Guard Selected
GUARD SENSE
-
+
A. Local Guard Sense
B. Remote Guard Sense
IN/OUT HIGH
IN/OUT HIGH
R
2
R
3
R
1
R
2
R
3
R
1
Figure 5-14
In-circuit ohms
measurements
using guard sense

Keithley 6430 Specifications

General

Type	Sub-Femtoamp Remote SourceMeter
Compliance Voltage	200 V
Maximum Output Voltage	200 V
Maximum Output Current	100 mA
Compliance Limit	Programmable
Interface	GPIB, RS-232
Input Impedance	>10^14 Ω