Photoanalysis System Calibration

By: Paul Chivers

Photoanalysis system data can be used for process control or to track relative changes without calibration. However, if your goal is to replace manual sieving then calibration is required. The calibration procedure outlined below is taken from the Calibration Document which is available to photoanalysis system users after logging into the Customer Download Area of the Downloads section of the WipWare website.

Calibration is the final step for system installation and cannot occur until all hardware and software adjustments have been characterized. These include mechanical setup; optical adjustments; scale settings; trigger settings; image quality settings and edge detection parameters. If any of these variables change, the system will require recalibration.

STEP 1: Stop Belt (perform a crash stop)

Once a system has been characterized and the process is running normally calibration can begin. Note that calibration is only effective if the material is unaffected by external variables not related to normal production (i.e., slower belts, partial process shutdown, etc…).

STEP 2: Image Material

In Delta, snap an image of the material. Save the image as ‘Calibration 1.bmp’ and close it. Place a scale reference (ruler, card, paper … of known dimensions) on top of the material in the viewable area. In Delta, snap another image and save it as ‘Scale 1.bmp’ before closing it.

STEP 3: Take Material for Sieving

In Delta, open the live image view. Find and mark the upper and lower limit of the viewable material on the belt. Remove the entire sample for sieving. Do not use coning, quartering, or riffling. The whole sample must be sieved.

STEP 4: Restart Belt & Sieve

All information has been gathered and your process can be restarted. Sieve the material before proceeding to next step.

STEP 5: Set Scale Factor

In Delta, open ‘Scale 1.bmp’ and set the scale using the scale reference of known length. Because the image was opened from a file, be sure the ‘Source’ is set to ‘Image File’. Close ‘Scale 1.bmp’.

STEP 6: Set EDPs

Open ‘Calibration 1.bmp’. Open the Options menu to get to the ‘Edge Detection Parameters’ tab and take note of which EDP preset is selected for the camera you are calibrating (i.e., Camera 1). Change the ‘Source’ to ‘Image File’ and select the same EDP preset from the previous step.

STEP 7: Set Size Classes

Select the ‘Output’ tab and take note of which Size Class preset is selected for the camera you are calibrating. Change the ‘Source’ to ‘Image File’ and select the same Size Class preset from the previous step. Make sure there is no calibration preset selected. Hit Apply and OK to save your changes.

STEP 8: Get Delta Values

Hit the ‘Generate Net’ button. Hit the ‘Sieve’ button. Take note of the following values: n, Xc, b, Xmax, X50. Save the chart as ‘Delta 1.bmp’. 

STEP 9: Enter Data into Calibration Sheet (See image to the right)