National Instruments 9211 User Manual download pdf (Page 9)

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

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National Instruments 9211 User Manual Page 9