Chapter 5 Connecting AI Signals on the USB-6210/6211 Devices
Using Non-Referenced Single-Ended (NRSE) Connections for Ground-Referenced Signal Sources
Figure 5-8shows how to connect ground-reference signal sources to the
USB-6210/6211 device in NRSE mode.
I/O Connector
AI <0..15>
or AI <16..n>
| Ground- | + | Instrumentation | |
| Amplifier | |
| Referenced | + | |
| Signal | Vs | | |
| – | | |
| Source | PGIA | + |
| Input Multiplexers |
| | | Measured |
| Common- | – | Vm |
| Voltage |
| Mode | AI SENSE | |
| AI GND | | |
| Noise | | – |
| | |
and Ground | + | |
Potential | |
Vcm | |
| M Series Device Configured in NRSE Mode |
| – |
| |
Figure 5-8.Single-Ended Connections for Ground-Referenced Signal Sources
(NRSE Configuration)
AI+ and AI– must both remain within ±11 V of AI GND.
To measure a single-ended, ground-referenced signal source, you must use the NRSE ground-reference setting. Connect the signal to one of
AI <0..31> and connect the signal local ground reference to AI SENSE. AI SENSE is internally connected to the negative input of the NI-PGIA. Therefore, the ground point of the signal connects to the negative input of the NI-PGIA.
Any potential difference between the device ground and the signal ground appears as a common-mode signal at both the positive and negative inputs of the NI-PGIA, and this difference is rejected by the amplifier. If the input circuitry of a device were referenced to ground, as it is in the RSE ground-reference setting, this difference in ground potentials would appear as an error in the measured voltage.
Using the DAQ Assistant, you can configure the channels for RSE or NRSE input modes. Refer to the Configuring AI Ground-Reference Settings in Software section of Chapter 4, Analog Input, for more information about the DAQ Assistant.