Delta RMC101 - Manual (Page 586)

RMC100 and RMCWin User Manual
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change in position units:
The RMC ensures that no fractional position units are lost in this conversion.
Determining the correct Scale and Prescale Divisor is a three-step process. First, the exact Scale
value is calculated assuming a Prescale Divisor of 1. Next, the optimum Prescale Divisor is
selected. Finally, the exact Scale is multiplied by the Prescale Divisor and rounded to the nearest
integer. The best way to do this is to use RMCWin’s Quadrature Calibration Utility. This utility
does all of these calculations for you, plus helps you select the appropriate position unit range. If
you do not choose to use this utility, follow the instructions in the steps below:
1. Calculating the Exact Scale Value
The precise scale value is calculated according to the following formula:
Therefore, the information required to calculate your exact scale is the number of position units
you want for a given number of counts. The Sign factor determines the direction your position
units move in relation to your counts; enter a 1 if increasing counts should increase the actual
position, or enter a 1 if increasing counts should decrease the actual position. For example, if you
have a 1000-line encoder and therefore 4000 quadrature counts per revolution, and you want to
have 3600 position units per revolution, then you would do the following calculation because you
want 3600 position units change when you have a 4000 quadrature count change:
One restriction you have at this point is that you cannot have more position units than counts over
a given range. That is, DPosition Units must be less than or equal to DCounts. If this is not the
case, you must either reduce the number of position units—usually dividing it by a factor of 10
accomplishes this—or choose an encoder that has more counts. For example, a user who
wanted 36000 position units per 4000 quadrature counts would need to upgrade to a 9000-or-
more-line encoder or drop to 3600 position units per revolution.
2. Selecting the Optimum Prescale Divisor
The Prescale Divisor can have values of 1, 2, 4, or 8. Because the Scale is divided by the
Prescale Divisor, this feature allows a fractional scale. Pick the largest Prescale Divisor you can
multiply the Scale by and still be between 32768 and 32768. For example, suppose your Scale
comes to 6324.70. The following table shows the possible Scales and Prescale Divisors you
could use and the effective scale:
Scale Divisor Effective
Scale Error from
6324.70
6325 1 6325/1 =
6325 0.005%
12649 2 12649/2 =
6324.5 0.003%
25299 4 25299/4 = 0.0008%