Gain for DSA Devices

On DSA devices, each gain setting corresponds to a particular range centered on 0 V. The gain settings are specified in decibels (dB), where the 0 dB reference is the default range of ±10 V.

For analog input operations, a negative gain value implies attenuation of the signal before the ADC, increasing the range beyond ±10 V. Thus, an input gain setting of –10 dB corresponds to an input range of ±31.6 V. On analog output, a negative gain value implies attenuation following the DAC. This decreases the output range. For instance, an output gain setting of –20 dB corresponds to an output range of ±1 V.

NI-DAQmx has three separate attribute/property sets you can use to control the hardware gain setting. Each has a different priority. If you write values to two or more of these attributes/properties that correspond to different hardware gain settings, the one with the highest priority will determine the hardware behavior.

• Gain Attributes/Properties—The gain attributes/properties AI.Gain and AO.Gain set the amount of gain to apply to the signal. These properties are set in decibels referenced to 10 V. These properties have the highest priority in NI-DAQmx.
• Range Attributes/Properties—The range attributes/properties AI.Rng.High, AI.Rng.Low, AO.DAC.Rng.High, and AO.DAC.Rng.Low define the maximum and minimum voltages you can acquire or generate. The range attributes/properties have a lower priority than the gain attributes/properties, but a higher priority than the maximum and minimum attributes/properties.
• Maximum and Minimum Attributes/Properties—The maximum and minimum attributes/properties AI.Max, AI.Min, AO.Max, and AO.Min specify values in engineering units that define the range. These attributes/properties have the lowest priority in NI-DAQmx. They are also the most commonly used since you can set them immediately when an NI-DAQmx task is created.