User's Manual

Chapter 4 Theory of Operation

For an example of a multiple-channel interval DAQ operation, refer to the

description of interval scanning signal timing in the Analog Input Timing

Connections section of Chapter 3, Connecting the Signals.

Data Acquisition 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 multiple-channel scanning, the acquisition 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 settle to the new input signal value to within 12-bit accuracy before

you perform an A/D conversion, or 12-bit accuracy is not achieved. The

settling time is a function of the selected gain.

Table 4-1 shows the recommended settling time for each gain setting

during multiple-channel scanning. Table 4-2 shows the maximum

recommended acquisition rates. For single-channel scanning, this rate is

limited by the ADC conversion period plus the sample-and-hold

acquisition time, which is specified at 10 µs(11µsifEXTCONV*isused).

Table 4-1. Analog Input Settling Time Versus Gain

Gain Setting Settling Time Recommended

1, 2, 5, 10 10 µsmax

20 12 µstyp,15µsmax

50 25 µstyp,30µsmax

100 60 µstyp,80µsmax

Table 4-2. DAQCard-1200 Maximum Recommended Data Acquisition Rates

Acquisition Mode Gain Setting

Sampling

Rate

Single channel 1, 2, 5, 10, 20, 50, 100 100 kS/s

Multiple channel

(observe these settings

to ensure 12-bit

accuracy)

1, 2, 5, 10 100 kS/s

20 83.3 kS/s

50 40.0 kS/s

100 16.6 kS/s