RESISTOMAT
®
Model 2302-V001
Page 24
Introduction &
applications
Description of functions
Brief guide
Operation
Calibration
Test and offset
instructions
RS232 data
output
Accessories and Circuit diagram
Test and offset
instructions
7.
Test the voltage display with the mV generator (e.g. 6705). Connect it
to + U / - U and adjust the left decade of the display from 0 to 2 (the display
ranges from 00000 to 20000). The voltages required for single steps are
Range
2 m
Ω
/3A
:
3 mV
20 m
Ω
/3A
:
30 mV
20 m
Ω
/1A
:
10 mV
200 m
Ω
/1A
:
100 mV
All other steps must also correspond with these in terms of voltage.
The fixed resistances R 12
÷
R 17 determine the gain.
8.
The digital voltmeter (Model 7122) contains zero and sensitivity adjusters
which can be accessed from the rear panel of the voltmeter.
P 4:
Zero
P 2:
Sensitivity
9.
If large zero deviations occur in the various ranges, the zero point of the
digital voltmeter must be tested. For this, it is sufficient to pull out amplifier
V 5 (turn off the device briefly) and then set the voltmeter to zero. The U board
must remain plugged in to bridge the input of the voltmeter.
10.
If the voltage display is consistently wrong as in item 7, the sensitivity trimmer
of the digital voltmeter can be readjusted.
11.
Roughly test the current steps with the ammeter connected to the I terminals.
12.
Connect the U terminals using Cu or brass clips to R 20 and R 21 as shown
in the sketch (arrows). Short-circuit the I terminals and select the range
20 m
Ω
/1 A. Trim P 5 to indicate zero (see the face plan at the end).
Explanation: The voltage measuring section of the 2302 is used here
as a zero voltmeter for setting the zero point of V 4. As the
required adjustment accuracy is
±
2
µ
V, the connection lines
must only consist of copper or brass. Soldering wires is
permissible, although the soldering points must be allowed
to cool. Terminals with steel springs generate large errors
due to thermal e.m.fs. The connection points on the board
must be selected exactly as specified. Large errors also
occur at other points on the same conducting track.
The zero point of V 4 may change by several
µ
V on
switchover of the measurement range.
13.
Connect a calibration resistance in the range 20
Ω
/1 mA. Using trimmer P 1,
adjust the I-Cal (front panel) display precisely. This trimmer acts on -10 V as
described in item 4 and, consequently, on all current steps.
