User`s manual

Operation Theory 57

ADLINK Technology Inc. PCI-9524

sampling rate. Also note that the output data rate is 29.5 SPS

rather than 60 SPS, due to auto-zeroing. As the sampling rate

changes, the notches' frequency change accordingly.

Figure 4-4: The Effect of Auto-zero on Thermal Noise and

1/f Noise, ADC running at 60 SPS

Effect of Auto-zero on Thermal noise and 1/f Noise

-120

-100

-80

-60

-40

-20

0.00 10.00 20.00 30.00 40.00 50.00 60.00

Frequenc y (Hz)

Attenuation (dB)

As many bipolar-input low-noise amplifiers, those used in PCI-

9524 start to assert their 1/f noise below 10 Hz, the gradually

increasing noise attenuation from below 20 Hz is a nice feature.

This also implies that a too-low sampling rate will not improve the

stability performance significantly, since noise attenuation may

start at a frequency much lower than where the amplifier's 1/f

noise emerges.

To successfully resolve low-level signals, always enable the auto-

zero and remote-sense function, keeping transducers and installa-

tion of PCI-9524 away from heat radiating sources, EMI radiating

sources, and free of mechanical vibration. Also, shield transducers

from airflow, and make sure all the connecting junctions are fas-

tened tight and free of oxidation.