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What is "Unipolar External Reference" or "Bipolar External Reference" in MAX?

Primary Software: Utility Software>>Measurement & Automation Explorer
Primary Software Version: 3.1
Primary Software Fixed Version: N/A
Secondary Software: Driver Software>>NI-DAQ, Driver Software>>NI-DAQmx

Problem:
In MAX there are four polarity choices on the AO tab in the Devices and Interfaces » Traditional NI-DAQ (Legacy) Devices » Your Device » Properties window. The choices listed are Unipolar, Bipolar, Unipolar External Reference, or Bipolar External Reference. What do these mean, and how do I use them?

Solution:
This information is available in the MAX help menu: Help » Help Topics » NI-DAQ » Traditional NI-DAQ. In the help file, expand the contents to Measurement & Automation Explorer » Getting Started » DAQ Devices » Configuring DAQ Devices » Analog Output. The following is documented in the polarity section: 
  • Bipolar -- a signal range that has both positive and negative values
  • Unipolar -- a signal range that is always positive
  • Bipolar External Reference -- a bipolar range that has a minimum and maximum value equal to the supplied external reference positive and negative values
  • Unipolar External Reference -- a unipolar signal that has a maximum value equal to the supplied external reference value

The external reference can also be applied programmatically by using the AO_Configure NI-DAQ Function Call or AO Config.vi in LabVIEW. Refer to the NI-DAQ Function Reference Manual for more information on how to use the AO_Configure function. Refer to the LabVIEW Help for more information on the Limit Settings input of the AO Config.vi. If you are configuring multiple analog output channels, the reference for each channel can be selected individually by using arrays for the Channel list and for the Limit Settings. The indices of the two input arrays correspond; therefore, different Limit Settings can be applied for different Channels. Programmatically configuring the AO polarity settings will take precedence over the MAX configuration.

Note: If you select one of the external reference selections, set the voltage in the External Reference Voltage selection box. The voltage that you are using as your external reference voltage should be connected to the EXTREF line on your DAQ device. For signal connections and limitations on the range of usable external reference voltage, see the reference manual for your DAQ device.

Note: If you are NOT using a Plug and Play Data Acquisition (DAQ) device or a parallel port DAQ device, you might need to set the analog input jumpers accordingly to match the Polarity/Range you selected. Refer to your hardware user manual for specific jumper settings.

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Report Date: 11/08/2001
Last Updated: 01/16/2008
Document ID: 2F777VGJ

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