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Fault clustering

 

Applies to

Sensoft Multiline
Sensoft Vision

 

Question

I would like to count a cluster of blisters as one fault instead of many. My specs allows this if the faults are less than 5 cm apart. Is this possible?

 

Answer

Yes. The answer here applies to Sensoft Vision, and to Sensoft Multiline with Sensystem type K12 (i.e. when the wire velocities are < 100 m/min). Sensoft Multiline with Sensystem type K2 (for high wire velocity) automatically clusters faults in the cm range.

How to enable clustering in Sensoft Multiline

To enable fault clustering for LU x, LU y, Lump and Neck-Down:

  1. Open the .ini configuration file in a text editor.
    It is most probably located in Documents\LabVIEW Data\Sensoft\Config Data\Configurations Multiline . An easy way to open it in a text editor is to click con the button Load... on page Settings, click with the right mouse button on the file and select Open with >
  2. Replace the All custom sensors block (i.e. all lines starting with "All custom sensors") with the text in this file. Note: the file contains µ signs for microns. To retain them you have to save and open it, copy & paste mangles them up
  3. Set the desired clustering range. By default, i.e. in the file linked just above, the clustering range is 0.1 m. To change it, change the value in all the lines  All custom sensors *.Max fault length \5Bm\5D = "0.1"
  4. Assert that you are using OPC UA and that there are at least 4 custom sensors per line. This is done easiest in the config file by checking that slightly above the All custom sensors block there are the lines
    Boxes 0.OPC parameters.Custom sensors per line = "4"
    Comm = "OPC UA"
How to enable clustering in Sensoft Vision
  1. On page Settings click on Show advanced settings
  2. Set Hysteresis [µm] to 15000. To do this you must first remove the checkmark near Auto
  3. Set Max fault length [mm] to the desired clustering range
  4. You may want to save the settings
How it works

A fault starts when the the signal measuring the diameter variation goes over a specified Threshold. It ends when the signal goes below Threshold minus Hysteresis, or if this does not happen, after Max fault length. A hysteresis prevents a noisy signal from generating fake faults, as is illustrated in Figure 3.

Figure 2: The Fault size is the maximum signal during the fault.The Fault length is the length with signal above threshold. The internal calculation uses a hysteresis to avoid problems with noisy signals (see Figure 3).

 

Figure 3: Without hysteresis a noisy signal could generate unwanted faults at the beginning or end of the fault. For example, the signal in this figure would, without hysteresis, generate three faults. To avoid this, the fault must cross Threshold minus Hysteresis to end. The Fault length is calculated from the first to the last time the signal crosses Threshold.

If now we set Hysteresis to a very large value (i.e. much larger than Threshold), then the fault always ends after Max fault length.

 

Caveats
  • Fault length - When using clustering, fault length is intended as cluster length, i.e. from the start of the first fault in the cluster to the end of the last fault of the cluster. This prevents, or at least complicates, using fault length in criteria. A criterion like Warning if LU x > 50 µm and long > 1 mm now matches, besides the desired long defects, also two short defects if they are a few millimeters apart. This may be no problem, since a) it is stricter than the specification, and b) we don't expect many additional matches. The other case, Warning if LU x > 50 µm and long < 1 mm, fortunately, rarely appears in specifications. Another caveat is that, in older software (up to Sensoft Vision 1.7.2 and Sensoft Multiline 1.2.4) the fault length was always the specified Max fault length.
  • Marker - If you operate a marker which is very near to the lump sensor (less than 30 cm), keep in mind that the defect is processed only after Max fault length has passed. With clustering the minimum marker distance is Max fault length larger than without clustering. The minimum marker distance without clustering is explained in the DO (Multiline) or DO (Vision) page. Keep also in mind that the marking range has to be larger than twice Max fault length plus reserve.