#### Performing a Low Level Matrix Calibration

The low level matrix contains the 3D or centered position of the probing device. You should redo the SP600 low level matrix calibration at these times:

- Whenever you remove the probe head

- Whenever you remounted the probe head

- Whenever you attached a new SP600 probe

- Whenever the SP600 sustains damage

- During periodic intervals based on your specific needs.

Prerequisites:

Before following the calibration procedure below, ensure that you meet these prerequisites:

- You must run PC-DMIS in online mode.

- You must run PC-DMIS using a CMM that has a lower matrix.

- If using a Leitz protocol controller from Brown and Sharpe / DEA, it must be configured to use a lower matrix. For this to be true it must have PRBCONF=0 in the controller settings.

- You must have an analog probe that utilizes a lower matrix. Some of these include the SP600, SP80, LSP-X1, LSP-X3, LSP-X5, and so on.

- You should use a rigid stylus that deflects as little as possible during the procedure. A common example of this for an SP600 is the 8x100 ceramic stylus.

Calibration Procedure:

1. Access the Probe Utilities dialog box (Insert | Hardware Definition | Probe).

2. Ensure that the angles you need exist in the Active Tip List.

3. From the Active Tip List select the angle used as the reference position. In most instances this should be the angle used for the Z- direction. Unless you have a horizontal arm, this angle is usually the T1A0B0 tip.

4. Click the Measure button. The Measure Probe dialog box appears.

5. Select the SP600 Lower Matrix option button from the Type of Operation area. This option only appears if you're working in online mode and have the SP600 probe setup inside the Probe Utilities dialog box.

6. If desired change the values in the Prehit / Retract, Move Speed, or Touch Speed boxes.

7. Select an appropriate tool from the List of Available Tools list.

8. Click the Measure button. PC-DMIS will give a warning message telling you that if you continue you will change the machine specific parameters for the lower level matrix on the controller itself. Click Yes to continue the calibration.

9. PC-DMIS will display another message asking if the qualification tool has moved. Click Yes or No.

10. PC-DMIS next displays a message asking you to take one hit normal to the calibration tool. If you're working from the Z- position, take the hit on the very top of the tool. After taking this one hit, PC-DMIS takes over and finishes determining the center location of the calibration tool. It does this by taking:

- 3 hits around the sphere.

- 25 other hits around the sphere.

11. Once PC-DMIS finds the center location of the tool, the actual low level matrix calibration begins. PC-DMIS automatically takes 20 hits (10 hits in one direction and 10 hits in another direction forming a cross pattern) on the X+, X-, Y+, Y-, and Z+ poles of the calibration sphere, for a total of 100 hits. This typically takes five to ten minutes to complete.

12. PC-DMIS then presents you with nine numbers along with a message asking if these numbers are correct. These are the lower level matrix values. If you started the calibration with the probe in the Z- direction then the ZZ value (value in the third row and third column) should be between about .14 and .16. All other values should be less than or about .1.

13. If the values are correct, click OK. PC-DMIS sends an emergency stop command to the machine and then overwrites the lower level matrix values on the controller with these newer values. PC-DMIS displays another message box asking you to start your machine.

14. Press the Machine Start button on your jog box.

15. Click OK on the message box.

PC-DMIS once again displays the Probe Utilities dialog box. Notice that the reference tip in the Active Tip List isn't calibrated. The lower level calibration doesn’t calibrate the actual tip angles. Tip angles get calibrated when you perform the upper level matrix calibration procedure.

Important: If you don't have a good low level matrix you will experience problems in some scanning routines and the machine may not be able to complete some scans. In addition you will experience inaccuracies.