21 |
+
-
USB-3200
AI+
AI-
AI-GND
+
-
Figure 3.4 balanced bias resistor differential input mode
For AC-coupled floating signal sources, a resistor is required to provide DC loops for the
positive input of instrument amplifier, AI+, as shown in Figure 3.5.
If the AC coupled float signal source has a smaller internal resistance, the AI+ and AI-GND
connection resistance values should be generally set
as 100kΩ to 1MΩ. Hence, it does n
ot
aggravate the load of the signal source, nor does it generate an offset voltage due to the bias
current of the instrument amplifier. In this case, you can directly connect AI- and AI-GND.
If the internal resistance of the AC coupled floating source signal is large, the differential input
mode utilizing the equilibrium bias resistor described earlier should be used, and it is important
to note the gain error that may be caused by the equilibrium bias resistor.
USB-3200
AI+
AI-
AI-GND
Figure 3.5 Differential input method for AC coupled floating signal source
Non-grounded reference single-ended mode (NRSE) connection
When both the following conditions are true, you can connect the float signal using a
non-grounded reference single-end mode:
The input signal voltage is higher than 1V