User manual

Chapter 4 Connecting Signals

Differential Connection Considerations (DIFF Input Configuration)

A differential connection is one in which the analog input signal has its

own reference signal or signal return path. These connections are available

when the selected channel is configured in DIFF input mode. In DIFF

mode, the analog input channels are paired, with ACH<i> as the signal

input and ACH<i+8> as the signal reference. For example, ACH0 is paired

with ACH8, ACH1 is paired with ACH9, and so on. The input signal is tied

to the positive input of the PGIA, and its reference signal, or return, is tied

to the negative input of the PGIA.

When you configure a channel for differential input, each signal uses

two multiplexer inputs—one for the signal and one for its reference signal.

Therefore, with a differential configuration for every channel, up to eight

analog input channels are available.

You should use differential input connections for any channel that meets

any of the following conditions:

• The input signal is low level (less than 1 V).

• The leads connecting the signal to the device are greater than

10 ft (3 m).

• The input signal requires a separate ground-reference point or return

signal.

• The signal leads travel through noisy environments.

Differential signal connections reduce picked-up noise and increase

common-mode noise rejection. Differential signal connections also allow

input signals to float within the common-mode limits of the PGIA.

UM.book Page 11 Monday, May 14, 2001 10:32 AM