National Instruments AT E Series Differential Connections for Nonreferenced or Floating Signal Sources

Chapter4 ConnectingSignals

ATE Series User Manual 4-22 ni.com

Differential Connections for Nonreferenced orFloating Signal Sources

Figure 4-7 shows how to connect a floating signal source to an AT E Series

device channel configured in DIFF input mode.

Figure4-7. Differential Input Connections for Nonreferenced Signals

Figure 4-7 showstwo bias resistors connected in parallel with the signal

leads of a floating signal source. If you do not use the resistors and the

source is truly floating, the source is not likely to remain within the

common-modesignal range of the PGIA, and the PGIA saturates, causing

erroneousreadings. You must reference the source to AIGND. The easiest

wayis simply to connect the positive side of the signal to the positive input

ofthe PG IA andconnect the n egativeside of the signal to AIGND as well

PGIA

SelectedChannel in DIFF Configuration

Programmable

Gain

Instrumentation

Amplifier

–

InputMultiplexers

AISENSE

AIGND

I/OConnector

–

ACH+

ACH–

Bias

Current

Return

Paths

Bias

Resistors

(seetext)

Floating

Signal

Source

Measured

Voltage