Delta RMC101 - Manual (Page 622)

RMC100 and RMCWin User Manual
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recommended that one of these utilities is used, but the underlying math is described below.
Method 1: P0/P1 Calculation
The simplest way is to physically measure the axis’s position at two points and read how many
counts the RMC reports at each position. If we call the two positions, in user position units, P0
and P1, and call the corresponding counts C0 and C1, the following two equations will give a
Scale and Offset. Notice that the Prescale Divisor is left out at this point; it is assumed to be 1:
Once the Scale is calculated, the Prescale Divisor can be calculated. The Prescale Divisor can
have values of 1, 2, 4, or 8. Because the Scale is always divided by the Prescale Divisor, you
essentially have a fractional scale. Pick the largest Prescale Divisor you can multiply the Scale by
and still be between 32767 and 32767. 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 =
6324.75 0.0008%
50598 8 Invalid scale Invalid
Therefore, in this example, a Scale of 25299 and a Prescale Divisor of 4 should be used.
These calculations can be done automatically using the Position Scale/Offset Calibration Utility
feature in RMCWin.
Method 2: Using the Transducer Resolution
The Scale can also be calculated mathematically using the SSI transducer’s reported resolution.
The following formula does this. Notice that the Prescale Divisor is left out at this point; it is
calculated after the initial Scale value has been calculated, as described in Method 1:
Scale = Resolution x Position Units/Resolution Unit x 32768 x Sign
In the above formula, Sign equals +1 when an extend move yields increasing Actual Position
counts, and -1 when an extend move yields decreasing Actual Position counts. Position Units are
generally 0.001 inches or 0.1 mm. The transducer resolution is often given in mm or µm.
Once the Scale and Prescale Divisor have been calculated, the Offset can be calculated: