Linear Interpolation with Excel

Linear interpolation is a straight line fit between two data points.

Many people want to interpolate data they have digitized with Dagra in Microsoft Excel. Unfortunately Excel doesn’t provide an interpolation function but there is a simple approach.

Digitize Datasheets with Dagra

LM35 thermal resistance digitized with Dagra

Numerical data from graphs in PDF datasheets can be easily incorporated into your analysis. Use Dagra to digitize the data: Import the graph from the datasheet into Dagra

Compare Data Sources

LED data sheet

Often it is informative to plot one set of data on top of another. While light-emitting diodes are created by combining several colors on a single chip. Although your eye sees color in discrete bands, careful selection of the composite colors can appear ‘white’.

Here the spectrum of two TT Electronics Ledium Series light emitting diodes are plotted with the CIE tristimulus curves.

Using Digitized Data in Matlab

Digitized data loaded into Matlab

Graphs digitized with Dagra can be loaded into Matlab in three ways:

  1. Dagra’s LoadDagra.m function for Matlab.
  2. Copied onto the clipboard and pasted into Matlab’s command line window, or
  3. Exported into a text file and imported using Matlab’s dlmread function.

The easiest method is using the LoadDagra.m function because you don’t need to create a separate file or fill up Matlab’s command buffer with the imported data.

Pasting Digitized Data into Excel

Digitized data pasted into Excel

Graphical data digitized using Dagra can be quickly transferred to Microsoft Excel, or any spreadsheet, using the system clipboard. Simply copy the data from Dagra. You can choose which series you want to copy. Then switch to Excel and choose Paste from the Home tab.

Energy falling on an Infrared Sensor

Built-in linear interpolation

Dagra was used in this example to trace the transmittance of a Fresnel lens so the data could be used in MathCad.

The goal of the project was to estimate how much energy from the skin of a person would be focused onto an infrared sensor. The lens had a lot of strong absorption bands in the wavelengths we were interested in so tracing the transmission from the manufacturer’s datasheet helped provide a more accurate model.

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