Open Current Loop Detection

Two NI-DAQmx Read/Write attributes/properties allow you to check for disconnected sensors. The first is OpenCurrentLoopChansExist. This attribute/property returns a Boolean true if one or more channels experience an open current loop condition. The second is OpenCurrentLoopChans. This attribute/property returns an array of strings indicating which channels (if any) experienced an open current loop condition. You must query the OpenCurrentLoopChansExist attribute/property before querying the OpenCurrentLoopChans attribute/property.

OpenCurrentLoopChansExist reads the open current loop condition from the device and caches it in the driver. Subsequent reads of OpenCurrentLoopChans attribute/property will read the open current loop channel information cached in the driver from the previous OpenCurrentLoopChansExist query.

Note

• NI-DAQmx returns all data whether or not an open current loop occurs. If your application requires open current loop checking, it is recommended that you read the open current loop attributes/properties after each call to Read. Your program should discard questionable data or return a flag when the driver reports an open current loop.
• For Analog Input devices with IEPE, the IEPE excitation current source must be enabled for open current loop detection to work. If IEPE is not turned on, an error is returned when OpenCurrentLoopChans is read.