National Instruments SCXI-1121 Manuel D’Utilisation

•

You also need a 120 

Ω

 1/4 W precision resistor with tempco less than 

or equal to 5 ppm, or an ammeter with the following specifications:

–

Accuracy:

±0.004% standard
±0.016% sufficient

–

Range:

0.5 mA

–

Resolution: 6 1/2 digits

•

If you use the resistor to calibrate the current excitation, you also need 
an ohmmeter with four-wire measurement and the following 
specifications:

–

Accuracy:

±0.004% standard
±0.016% sufficient

–

Range:

200 

Ω

–

Resolution: 5 1/2 digits

A multiranging 5 1/2-digit digital multimeter can provide you with most of 
the necessary functions described previously. We will refer to the 
measuring instrument as a digital multimeter (DMM).

Each channel on the SCXI-1121 has two potentiometers dedicated for 
calibration. For the amplifier channels, one potentiometer is used to null the 
output offset; the other is used to null the input offset. On the excitation 
channels, one potentiometer is used to adjust the voltage reference, while 
the other is used to adjust the current source.

Follow these steps to null the offset of the amplifier channels:

1.

Short the inputs of the DMM together and then connect them to chassis 
ground.

2.

Record the measurement indicated by the DMM display. This is the 
DMM inherent offset and should be subtracted from subsequent 
measurements.

3.

Short the channel inputs of interest together and then to chassis 
ground.

4.

Set the amplifier gain to 1.

5.

Connect the amplifier output to the DMM. Make sure that the DMM 
can achieve the accuracy and resolution you need.

6.

Adjust the output potentiometer of the channel of interest until the 
output is 0 ± 3 mV.

7.

Set the amplifier gain to 1,000.