Chapter 6 Connecting AI Signals on the USB-6215/6218 Devices

The differential connection configuration allows the common-mode noise voltage, Vcm, to be rejected during the measurement of V1.

You must connect the negative lead of your sensors and AI GND to a local ground signal on your system.

Referenced Single-Ended (RSE) Measurements

Using the RSE measurement configuration allows the USB-6215/6218 to take measurements on all AI channels when all channels share a common ground. Refer to Figure 6-2for an illustration of an RSE connection configuration.

Note If you leave the AI GND pin unconnected, the signals will float outside the working input range of the USB-6215/6218, which may result in unreliable measurements because there is no way to ensure that the input signal is within 10 V of AI GND.

AI1

MUX

PGIA

ADC

AI2

AI GND

USB-6215/6218

Figure 6-2.Connecting a Device to a USB-6215/6218 Using RSE Connections

In an RSE connection configuration, each input channel is measured with respect to AI GND.

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NI USB-621x User Manual