Delta RMC101 - Manual (Page 621)

SSI 6.6
Transducer Interface Modules 6-77
For general scaling information, see the Scaling Overview topic.
Because the RMC uses 16-bit positions, positions must all fit within a range of 65,536 position
units. Because position units are user definable, this range does not limit most applications. See
the section below on defining position units.
For SSI axes, the Offset parameter is used with the Scale parameter to define the position range.
If the Scale parameter is negative, then the position range extends from the Offset value minus
65535 up to the Offset value. If the Scale parameter is non-negative, then the position range
extends from the Offset value up to the Offset value plus 65535. The following chart summarizes
this concept:
Scale Min. Position Max. Position
< 0 Offset - 65535 Offset
³ 0 Offset Offset + 65535
However, because the Offset is also used to convert transducer counts to position units, it cannot
be set independently.
Translating to Position Units
Before the translation from counts to position units begins, the Count Offset SSI configuration
setting is applied to the counts. This means that the value of the Count Offset is subtracted from
the Counts before they are displayed or processed in any way. For a full discussion on the use of
the Count Offset setting, see SSI Configuration.
The Scale, Offset, and the Prescale Divisor bits of the Configuration word parameters are used to
define position units as a function of transducer counts. Below is shown an example SSI and the
effect of the Scale, Offset, Extend and Retract Limits:
The following formula summarizes the translation from transducer counts to Actual Position units:
As described above, the Counts field has already had the Count Offset configuration setting
subtracted from it before using this formula. If the Actual Position overflows the valid 16-bit
position range, as described above, the Position Overflow bit will turn on, forcing the axis to halt.
Notice that the Scale can hold values from -32768 to 32768, but 16-bit signed numbers are
limited to -32768 to 32767. Therefore, enter a scale of 32768 as 0; the RMC will interpret it as
32768.
There are two main ways to calculate the Scale, Offset, and Prescale Divisor bits. Each method is
described below. Notice that both have automatic Calibration Utilities built into RMCWin. It is