The previous part of the tutorial finished the compression correction of the tutorial sample; this part of the tutorial will show you how to use the trim function to remove a possible edge effect in the low pressure range of the data. The trimming tool can only be used after the compression correction has been done, as it does not make sense to trim the data before correcting for compressibility.
If you are still zoomed in to the top part of the curve, click on the Zoom out icon at the top of the graph to reveal the entire curves.
Click in the Enable trimming option at the top of the graph. Once it is enabled, the graph will show red slider lines on the left and right hand side of the graph. In the box at the top of the each red line is the currently selected pressure and equivalent capillary diameter calculated using the properties of mercury from the sample data. Trimming the data does not change the original data file, it merely reduces the range of pores and throats that PoreXpert needs to model. The porosity also changes on trimming; this is the porosity which you have chosen to be modelled, which may or may not be the complete porosity of the sample.
The trim feature will only trim where there is an experimental data point. To move the trim line, left click within the top data box above the line, and drag the line sideways. (You may have to try several times to pick up the red line with the mouse.)
For the tutorial example, we are going to trim the low pressure side (left hand side of the graph) close to 0.1 MPa, and look to see how this affects the Results shown on the right hand side of the graph. Drag the left-hand line and its box until the box displays 0.0894 MPa and 16.6233 µm as shown:
Click on the Trim button. (If you make a mistake you can click on the Undo button and it will reset the data to the full pressure range.) The next figure shows the trimmed graph with the updated results.
PoreXY home screen after the tutorial data has been trimmed
As can be seen, the trimming of the data at close to 0.1 MPa makes a large difference to the porosity values. By trimming the data, you are indicating that you only wish PoreXpert to model the intrusion above 0.09 MPa (16.6 µm) - probably because you think that below this pressure the intrusion is between particles (inter-particle), or into void features near or at the surface of the sample, whereas you wish to model the void features within individual particles (intra-particle) or in the bulk of the sample. It can also be easier to find a fit to the data once it has been trimmed, but this should not be the reason for trimming it.
Other examples of trimming are for the TypeA (two layer) sample before and after trimming, and for sample MR9 before trimming, as shown below.
Type A sample before trimming
Type A sample after trimming
Sample MR9 before trimming
The next stage of the tutorial is exporting the data to PoreXpert and saving data.