ETS-Lindgren 2181 Turntable - Manual (Page 28)

28 | Operation
Turntable Encoder Calibration
Parameter C, the encoder calibration parameter, calibrates the encoder counts to
the rotation of the turntable. For the Model 2181, parameter C must be set to
3660. This setting is used to convert the encoder count values returned from a
motor base into the corresponding centimeter or degree position reading. For
turntables, this represents the number of encoder counts per revolution.
If the given value does not work correctly, the encoder calibration value can be
determined using the following procedure:
1. Set the encoder calibration value to 3600.
2. Make sure the turntable is positioned to allow more than a full revolution
of travel in the CW direction. Use the STEP keys to run the turntable CW
a few degrees to remove any play in the turntable.
3. Using masking tape, mark the current location of the turntable against
the ground ring, and set the current position reading to 000.0.
4. Using the STEP keys, rotate the turntable CW until it is again aligned
with the mark on the ground ring. For best results, the last motion should
always be in the CW direction to account for any play in the gearing
between the motor and encoder.
5. Record the reading of the display, ignoring the decimal point. For
example, 360.0 would be 3600. This is the encoder calibration value.
If the value is below 3600, the resolution of the encoder is low and the controller
will not provide 0.1-degree resolution, even though the display shows that digit.
If the value is past 9999, the encoder has too many counts per meter and the
controller cannot correct for it. In this case, contact ETS-Lindgren for
assistance.
6. Enter the encoder calibration value and reset the limits and position
information.
7. Test the turntable by moving it a complete revolution and comparing the
alignment marks. It may be necessary to adjust the encoder calibration
value up or down slightly depending on the result.
When scanning between limits, it is not uncommon to have a small discrepancy
between the absolute position of the table and the display on the controller.
This is because reversing the direction of rotation reverses any gear play
between the encoder and the table top, allowing that play to be visible in the
positioning accuracy.