National Instruments NI 4495, Процедура калибровки, Страница: 16 / 22

NI 449
x
Calibration Procedure | © National Instruments | 15
3. Create and configure an AI voltage task on the NI 449x as shown in Table 18.
4. If verifying an NI 4492/4497/4499 and the coupling changes from DC to AC, commit the
configuration using the DAQmx Control Task VI and wait 5 seconds for the input to settle.
5. Start the task.
6. Acquire readings with the NI 449x.
7. Stop and clear the task.
8. Measure the exact frequency of the acquired signal around 10 kHz. The ratio between the
measured frequency and the actual input frequency represents the timebase frequency
accuracy. As an example, a measured value of 10.0002 kHz represents an accuracy of
20 ppm.
Adjustment
Performing the calibration adjustment procedure automatically updates the calibration
constants, date, and temperature in the EEPROM on the NI 449x device. There are two different
adjustment procedures. One applies to the NI 4495/4496/4498 devices. The other applies to the
NI 4492/4497/4499 devices.
Analog Input Adjustment for NI 4495/4496/4498 Devices
Complete the following steps to calibrate the analog input of an NI 4495/4496/4498 device:
1. Connect the output of the calibrator to all input channels on the device, using the BNC
T-connectors to split the signal in a tree formation to all the inputs.
2. Configure the calibrator to output a 200 mV
rms
signal at 1 kHz.
Table 18. NI 449x Timebase Frequency Accuracy Verification Configuration
Configuration Value
Minimum value –10.0
Maximum value 10.0
Terminal configuration Pseudodifferential
Acquisition mode Finite number of samples
Rate 40,000.0
Samples per channel 2,560,000
Gain 0 (dB)
Physical channel Dev_name/ai0
*
Coupling If verifying an NI 4495, DC. Otherwise, AC.
* Dev_name is the name shown for the NI 449x in MAX.