ADLINK USB-2401 - Manual (Page 39)

Operation 29
USB-2401
100 times the equivalent source impedance, such that if the
source impedance is less than 100Ω, the negative side of the
signal needs only be connected to GND as well as the negative
input of the Instrumentation Amplifier without any resistors.
Connection of a floating signal source to the USB-2401 in
differential input mode is as shown.
Figure 3-3: Floating Source and Differential Input
3.3.2 Current Input Mode
Current signal source can be floating or grounded reference,
converted to voltage through a precision 249.5Ω resistor.
Cross-voltage on the precision resistor is considered differential
signal. The differential signal pair passes through differential
amplifier buffers and is measured by the analog-to-digital
converter chip (ADC) with ±2.5 V input range.
The formula to calculate voltage-to-current conversion is:
AI-
AI+
Floating signal source
GND
Amplifier
Amplifier
USB-2401
6701527 . 18
) (
) (
volt V
mA Current =