Model 2302-V001
RESISTOMAT
®
Page 9
Brief guide
Operation
Calibration
Test and offset
instructions
RS232 data
output
Introduction &
applications
Description of functions
Accessories and Circuit diagram
I = const.
R
LU
+ U
- U
+ I
- I
R
X
}
}
R
LI
R
LI
DVM
R
L
beeinflusst Ergebnis nicht
Introduction &
applications
R
L
does not influence the result
Figure 2: RESISTOMAT circuit
The current driven through the object under test is completely independent of variations in
the bridge resistance (object under test plus supply lines), at least as long as the compliance-
voltage limit of the current source is not exceeded. This implies 5 V at 3 A for Model 2302.
The limits for lower currents are considerably higher.
They are, by nature, influenced by variations in the grid voltage. The indicator lamp below
the measurement terminals provides a simple means of checking in a closed measurement
circuit.
The measurement voltage tapped at the object under test is supplied to the high-impedance
input of the voltmeter. Variations of a few kilo-ohms here do not influence the result at all.
This prevents errors from being generated due to excessively small line cross-sections in
the voltage path; at the same time, the influence of current lines can be checked easily by
measuring the voltage across the + I / - I terminals.
Even this is rendered superfluous by the indicator lamp between the terminals which comes
on if the critical compliance-voltage is attained. At this point, the display of measurement
values becomes unstable which constitues a further warning.
