Delta RMC101 User Manual download pdf (Page 586)

100

101

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

6325/1 =

6325

0.005%

12649

12649/2 =

6324.5

0.003%

25299

25299/4 =

0.0008%

1 2 ... 581 582 583 584 585 586 587 588 589 590 591 ... 950 951

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Delta RMC101 User Manual Page 586

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