ADLINK Technology USB-2401, User Manual

Page: 39 / 60

Operation 29
USB-2401
100 times the equivalent source impedance, such that if the
source impedance is less than 100
ȍ
, 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 249.5
Ÿ
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 =