Data Acquisition Toolbox

Linearly Scaling the Data: Engineering Units

The Data Acquisition Toolbox provides you with a way to linearly scale data as it is being queued in the engine. You can associate this scaling with specific engineering units such as volts or Newtons that you might want to apply to your data.

The properties associated with engineering units and linearly scaling output data are given below.

Table 6-11: Analog Output Engineering Units Properties

Property Name	Description
OutputRange	Specify the range of the analog output hardware subsystem.
Units	Specify the engineering units label.
UnitsRange	Specify the range of data as engineering units.

For many devices, the output range is expressed in terms of the gain and polarity.

Note    You can set the engineering units properties on a per-channel basis. Therefore, you can configure different engineering unit conversions for each hardware channel.

Linearly scaled output data is given by the formula

scaled value = (original value)(output range)/(units range)

The units range is given by the UnitsRange property, while the output range is given by the OutputRange property. UnitsRange controls the scaling of data when it is queued in the engine with the putdata function. OutputRange specifies the gain and polarity of your D/A subsystem. You should choose an output range that encompasses the output signal, and that utilizes the maximum dynamic range of your hardware.

For sound cards, you might have to adjust the volume control to obtain the full-scale output range of the device. Refer to Sound Cards to learn how to access the volume control for your sound card.

For example, suppose OutputRange is [-10 10], and UnitsRange is [-5 5]. If a queued value is 2.5, then the scaled value is (2.5)(20/10) or 5, in the appropriate units.

Note    The data acquisition engine always clips out-of-range values. Clipping means that an out-of-range value is fixed to either the minimum or maximum value that is representable by the hardware. Clipping is equivalent to saturation.

Examples: Using Callback Properties and Callback Functions

Example: Performing a Linear Conversion