Chapter 3
Adjustment
©
National Instruments Corporation
3-15
Determining the Gains of the Six Post-Amplification
Attenuators (Constant A9)
These attenuators correspond to 1, 2, 4, 8, 16, and 32 dB of attenuation.
A9_UNTERMINATED refers to the array of gains of the attenuators in the
unterminated case and A9_TERMINATED refers to the gains of the
attenuators in the terminated case. A9TA corresponds to the gain of the
analog channel into a terminated load with no attenuation. You generate a low
frequency sine wave, enable the attenuators one at a time, and measure output
at each step. You can measure the amplitude, peak-to-peak, or RMS, as long
as all measurements are consistent.
1.
Make sure the output is unterminated.
2.
Set the gain calibration DAC to –4079 (the approximate value for a gain
of 1) by calling the function
ni54xx_SetGainDAC
. Set the following
parameters:
•
sessionHandle
—The handle of the calibration session for the
device
•
DACValue
— –
4079
3.
Set the offset calibration DAC to 0 by calling the function
ni54xx_SetOffsetDAC
. Set the following parameters:
•
sessionHandle
—The handle of the calibration session for the
device
•
DACValue
—
0
4.
Generate a 10 V sine wave at 500 Hz by calling the function
ni54xx_GenerateWaveform
. Set the following parameters:
•
sessionHandle
—The handle of the calibration session for the
device
•
waveType
—
NI54XX_SINE
•
amplitudeInVolts
—
10
•
frequencyInHz
—
500
5.
Measure the outputs (
lowFrequencyAmplitude
).
Enable each attenuator individually and measure the output amplitude.