All input channels share a common ground, COM, that is isolated from other modules in the system. The device's common-mode range is the maximum voltage between any channel and COM. The NI 9213, NI 9214, and NI PXIe 4353 measures the common-mode voltage level of each channel, and its over-range status can be monitored in NI-DAQmx.
To determine if a common-mode over-range detection has occurred, use the Common Mode Range Error Channels Exist and Common Mode Range Error Channels properties within the DAQmx Read property node. Common Mode Range Error Channels Exist returns a Boolean of true if one or more channels exceed the common-mode input range since the last time the property was queried, and Common Mode Range Error Channels returns the names of the virtual channels that exceed the common-mode input range.
If a common-mode voltage out of range is detected, the accuracy of the data on any channel in the task may be impacted. If a thermocouple is connected to the device, but is not in the task, make sure the channel does not exceed the common-mode voltage range. A floating thermocouple, or a channel that is left unconnected, will not exceed the common-mode voltage range. Refer to the devices Specifications document for more information about the common-mode voltage range.