You can create custom scales of various types in LabVIEW SignalExpress in order to present your data in a more usable form. Once you have established a step in SignalExpress, expand the Custom Scaling
drop-down menu and select Create New...
This will open the Create New NI-DAQmx Scale
You will then select the type of scale you would like to apply to your measurement. The scale types are described in the panel on the left as follows:
- Linear--Scales values by using the equation y=mx+b, where x is a prescaled value and y is a scaled value.
- Map Ranges--Scales values proportionally from a range of prescaled values to a range of scaled values.
- Polynomial--Scales values using an nth order polynomial equation.
- Table--Maps an array of prescaled values to an array of corresponding scaled values, with all other values scaled proporitonally.
Finally, you will be prompted to select a name for your scale.
For the pressure example previously mentioned, lets assume the pressure transducer we are using outputs a voltage range from 0-5V
corresponding to a pressure range of 0-100psi
on a linear scale. To apply this, you would select Linear
for the scale type, select a name for the scale and click Finish
. You will then be presented with the DAQ Assistant window:
In this window, enter the name of the units you will be scaling to in the Scaled
box--for this example,
. You can then apply the Scaling Parameters used to convert Volts to psi:
Slope = 100 psi
÷ 5 Volts
= 20 psi/Volt
Y-Intercept = 0 psi
Using these parameters, a voltage measurement of 3.4V would be presented as 68 psi. Click OK
to accept the settings. The amplitude of the acquired signals will now be in units of psi when collecting data.