Model 2302-V001
RESISTOMAT
®
Page 11
Brief guide
Operation
Calibration
Test and offset
instructions
RS232 data
output
Introduction &
applications
Description of functions
Accessories and Circuit diagram
Description of functions
Description of functions
General information
The principle of current and voltage measurement for resistances is initially represented by
two completely separate blocks of functions:
The multi-range constant-voltage source and the highly-sensitive digital voltmeter.
Both components are controlled via coupled switches which comprise the range
selector on the front panel.
The measuring current and voltage sensitivity are matched together so as to
provide readings directly in m
Ω
or
Ω
in accordance with Ohm's law using the
decimal point and units lamps which are also controlled.
Current source
An electronic control circuit supplies the current which was set and displayed using the range
selector, as soon as the external current path is closed. The currents are calibrated within
the overall limits of accuracy of the device; fluctuations caused by interfering factors (mains
voltage, load) are smaller than 0.001 % or 0.003 % in the worst case; consequently, the
highest possible indicated resistance of 20.000 would fluctuate by just one digit (given a
stable test unit).
However, current sources also have driving voltages which impose a limit on the voltage
drop across the load resistance.
The current generator also contains the automatic temperature compensation for copper
test units. When the mode switch is on the appropriate setting, the current changes
with the temperature of the test unit such that the voltage drop across the latter always
corresponds to the value for 20
°
C.
The compensating signal for the current is supplied continually by a Model 2391 sensor.
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