Measurement Computing USB-1208FS-Plus-OEM - Manual (Page 11)

USB-1208FS-Plus-OEM User's Guide Functional Details
11
Signal connections
Analog input
You can connect up to eight analog input connections to the header connector pins 1 to 20.
You can configure the analog input channels as eight single-ended channels ( CH0 IN through CH7 IN) or four
differential channels ( CH0 IN HI/LO through CH3 IN HI/LO ). When configured for differential mode, each
analog input has 12-bit resolution. When configured for single-ended mode, each analog input has 11-bit
resolution, due to restrictions imposed by the A/D converter.
Single-ended configuration
When configured for single-ended input mode, the input signal is referenced to signal ground ( GND ) and
delivered through two wires:
 Connect the wire carrying the signal to be measured to
CH# IN .
 Connect the second wire to
AGND .
The input range for single-ended mode is ±10 V. The Single-ended mode pinout is shown in on page 10.
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
CH# IN HI .
 Connect the wire carrying the reference signal to
CH# IN LO .
 Connect the third wire to
GND .
The Differential mode pinout is shown in on page 10.
Note : To perform a single-ended measurement using differential channels, connect the signal to CH# IN HI and
ground the associated CH# IN LO input.
A low-noise precision programmable gain amplifier (PGA) is available on differential channels to provide gains
of up to 20 and a dynamic range of up to 12-bits. Differential mode input voltage ranges are ±20 V, ±10 V,
±5 V, ±4 V, ±2.5 V, ±2.0 V, ±1.25 V, and ±1.0 V.
In differential mode, the following two requirements must be met for linear operation:
 Any analog input must remain in the −10V to +20V range with respect to ground at all times.
 The maximum differential voltage on any given analog input pair must remain within the selected voltage
range.
The input [common-mode voltage + signal] of the differential channel must be in the
−10 V to +20 V range in
order to yield a useful result.