![National Instruments SCXI-1121 Скачать руководство пользователя страница 76](http://html2.mh-extra.com/html/national-instruments/scxi-1121/scxi-1121_user-manual_3488771076.webp)
Chapter 3
Theory of Operation
3-14
www.natinst.com
This procedure calibrates the 10 V and 450 µA levels at the same time but
the accuracy achieved is limited to ±0.2%. To achieve better accuracies at
these levels, follow the procedure indicated above but set the excitation
levels to 10 V and to 450 µA instead of 3.333 V and 150 µA. If you do so,
the lower excitation levels of this channel will then be calibrated to ±0.2%
instead of to 0.04%. In the factory, the module is calibrated for 3.333 V and
150 µA.
You can seal the potentiometers after calibration with antisabotage lacquer
to avoid tampering with the calibration.
Table 3-2 lists the potentiometer reference designators that correspond to
each channel.
The resistor used to calibrate the current level must be a precision type with
a tempco of 5 ppm or less. You should measure and record the resistor value
before each calibration procedure. The DMM you are using should provide
you with the required resolution and accuracy to achieve the calibration
levels indicated in the paragraphs above. Annual or semi-annual calibration
is recommended to maintain the accuracy level.
Table 3-2.
Calibration Potentiometer Reference Designators
Input Channel
Number
Amplifier Channel
Excitation Channel
Input Null
Output Null
Voltage Mode
Current Mode
0
R2
R3
R10
R7
1
R16
R4
R20
R17
2
R26
R5
R30
R27
3
R36
R6
R40
R37