National Instruments 9211 - Manual (Page 9)

© National Instruments Corporation 9 USB-9211/9211A User Guide and Specifications
Figure 7. High Voltage Screw Terminal Backshell
USB-9211/9211A Circuitry
The USB-9211/9211A channels share a common ground that is isolated
from the chassis and the host computer. Each channel has an impedance
between the TC
+ and COM terminals and between the TC– and COM
terminals. Each channel is filtered and then sampled by a 24-bit
analog-to-digital converter (ADC). There is a current source between the
TC+ and TC– terminals. If an open thermocouple is connected to the
channel, the current source forces a full-scale voltage across the terminals.
Effects of Source Impedance on Voltage Measurement Accuracy
The resistors shown in Figure 8 produce an input impedance at the
terminals of the USB-9211/9211A.
1 Strain Relief
1