4

Analog Input

Figure 4-1shows the analog input circuitry of NI 621x devices.

I/O Connector

Isolation

Barrier

(USB-6215

and USB-6218

devices only)

AI <0..n>

MUX

DIFF, RSE,

NI-PGIA

ADC

AI FIFO

Digital

AI Data

or NRSE

Isolators

 

 

 

 

AI SENSE

AI GND

Input Range

Selection

AI Terminal

Configuration

Selection

Figure 4-1.M Series Analog Input Circuitry

Analog Input Circuitry

I/O Connector

You can connect analog input signals to the M Series device through the I/O connector. The proper way to connect analog input signals depends on the analog input ground-reference settings, described in the Analog Input Ground-Reference Settings section. Also refer to Appendix A, Device-Specific Information, for device I/O connector pinouts.

MUX

Each M Series device has one analog-to-digital converter (ADC). The multiplexers (MUX) route one AI channel at a time to the ADC through the NI-PGIA.

© National Instruments Corporation

4-1

NI USB-621x User Manual