National Instruments PCI-1200 - Manual (Page 62)

Chapter 4 Theory of Operation
PCI-1200 User Manual 4-10 © National Instruments Corporation
DAQ Rates
Maximum DAQ rates (number of samples per second) are determined by
the conversion period of the ADC plus the sample-and-hold acquisition
time. During multichannel scanning, the DAQ rates are further limited by
the settling time of the input multiplexers and programmable gain
amplifier. After the input multiplexers are switched, the amplifier must be
allowed to settle to the new input signal value to within 12-bit accuracy
before you perform an A/D conversion, or 12-bit accuracy will not be
achieved. The settling time is a function of the gain selected.
Table 4-1 shows the recommended settling time for each gain setting
during multichannel scanning. Table 4-2 shows the maximum
recommended DAQ rates for both single-channel and multichannel data
acquisition. For single-channel scanning, this rate is limited only by the
ADC conversion period plus the sample-and-hold acquisition time,
specified at 10
µs. For multichannel data acquisition, observing the DAQ
rates in Table 4-2 ensures 12-bit resolution. The hardware is capable of
multiple scanning at higher rates than those listed in Table 4-2, but 12-bit
resolution is not guaranteed.
Table 4-1. Analog Input Settling Time Versus Gain
Gain
Settling Time
(Accuracy ±0.024% [±1 LSB])
1 10 µs typ, 14 µs max
2–10 13 µs typ, 16 µs max
20 15 µs typ, 19 µs max
50 27 µs typ, 34 µs max
100 60 µs typ, 80 µs max
Table 4-2. PCI-1200 Maximum Recommended DAQ Rates
Acquisition Mode Gain Rate
Single-channel 1, 2, 5, 10, 20, 50, 100 100 kS/s
Multichannel 1
2, 5, 10
20
50
100
100 kS/s
77 kS/s
66.6 kS/s
37 kS/s
16.6 kS/s