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Chart 3 – Calibration Errors
When the machine prompts you to set the pens on zero the software resets the encoder to zero. When you move the arms to the 100% line the software counts up using the 74193 chip on our circuit board the amount of pluses generated by the encoder. When you depress the foot pedal on the 100% line the software creates a linear table from the zero (0) line to the 100% line. At this time the software prompts you to place the pens on a line from 30% to 70%. The software then checks the physical location of the pen and the optical parallax of the operator to confirm calibration of the encoder. The allowable difference should be less than 0.15%. If more than 0.15% you should recalibrate the 0 and 100% lines. If you cannot calibrate to within this tolerance, check the following:
- Pen arms for loose bearing or pen arm bearing adjustment screw has come loose. Tighten.
- Calibration chart center is worn. Replace with a new one.
- Encoder is loose in the outside bracket or has a loose shaft clamp. Tighten
- Steel tapes or cables on the operating arm centers under the top may be loose or riding up on centers. Loosen screw holding the tape. Correct then retighten.
- Bad I.C. chip on circuit board. Replace board.
- Bad or weak encoder. Replace encoder:
To check encoder and circuit board, in the calibrate menu depress calib arms to view raw encoder data. Pull the arms to the outer stops and make a note of the value of the encoder (10,200 to 11,500) then move the arms back and forth rapidly several times without hitting the stops the pull the arms back to the outer stops. The counts should remain the same within 10 counts. Repeat the procedure several times if the counts hold, then the encoder and circuit board are “OK”. Check for ground strap between the metal base and the P.C. Static electricity will cause intermittent calibration errors and the ground strap will help to stop the problem.