Chapter 5 Connecting AI Signals on the USB-6210/6211 Devices
| | | AI+ |
| Floating | + | |
| Signal | |
| Vs | |
| Source | |
| – | |
| | |
| | | AI– |
| R is about | R | AI SENSE |
| 100 times |
| | |
| source | | AI GND |
| impedance | | |
| of sensor | | |
Figure 5-2.Differential Connections for Floating Signal Sources with Single Bias
Resistor
You can fully balance the signal path by connecting another resistor of the same value between the positive input and AI GND on the USB-621xdevice, as shown in Figure 5-3.This fully balanced configuration offers slightly better noise rejection, but has the disadvantage of loading the source down with the series combination (sum) of the two resistors. If, for example, the source impedance is 2 kΩ and each of the two resistors is
100kΩ, the resistors load down the source with 200 kΩ and produce a –1% gain error.
