Measurement Computing USB-231-OEM, User Manual, Page: 12 / 26

USB-231-OEM User's Guide Functional Details
12

AI FIFO
—The DAQ device can perform both single and multiple analog-to-digital conversions of a fixed or
infinite number of samples. A first-in-first-out (FIFO) buffer holds data during AI acquisitions to ensure no
data is lost.
 ADC Control
—The ADC control circuitry sets the conversion rate of the ADC, sets the input
configuration, drives the scanning sequence, and starts acquisitions synchronous with the TRIG or CTR
signal
Single-ended configuration
When configured for SE input mode, the input signal is referenced to analog ground (
AGND
) and delivered
through two wires:

Connect the wire carrying the signal to be measured (
CHxH
or
CHxL
).

Connect the second wire to
AGND
.
The input range for single-ended mode is ±10 V. The single-ended mode pinout is shown in the Single-ended
mode pinout section on page 11.
Differential configuration
When configured for differential input mode, the input signal is measured with respect to the low input and
delivered through three wires:

Connect the wire carrying the signal to be measured to
CHxH

Connect the wire carrying the reference signal to
CHxL

Connect the third wire to
AGND
.
The differential mode pinout is shown in the Differential mode pinout section on page 10.
Note
: To perform a single-ended measurement using differential channels, connect the signal to
CHxH
and
ground the associated
CHxL
input.
Input range
The USB-231-OEM has an input range of ±10 V. For DIFF mode, each AI should stay within ±10 V with
respect to AGND, and the voltage between positive and negative inputs should be lower or equal to ±10 V. For
SE mode, signals of ±10 V at any analog input connector with respect to AGND are accurately measured.
Beyond ±10 V, the input signal begins clipping as shown in Figure 4. Typically, this clipping begins at ±10.5 V.
Figure 4. Analog input exceeding ±10 V returning clipped results