Delta RMC151 User Manual
Page 37
2 Starting Up the RMC
To have any useful meaning, the counts from the transducer must be scaled to position units.
The Position Scale and Position Offset parameters define the position units as a function of
transducer counts. This topic describes how to correctly calculate these parameters for an MDT
transducer.
Delta Recommends using the Scale/Offset Wizard for scaling the position. If you need to do it
manually, read this topic.
Scaling Counts to Position Units
The RMC calculates the Actual Position every control-loop time using the following
formula:
Actual Position [pu] = (Counts [cnt] x Position Scale [pu/cnt]) + Position Offset [pu]
Note:
If the Actual Position filter is applied, the RMC filters the Actual Position after calculating it with
the above formula.
Manually Calculating the Scale and Offset
The Scale/Offset Wizards provide the easiest method of scaling your axis. If you prefer to
do it manually, read this section.
Determining the Scale and Offset
There are two methods of finding the correct Position Scale and Position Offset.
Method 1: P
0
/P
1
Calculation
The accuracy of this method depends on how accurately you can measure two positions
of the axis.
1. Physically measure the axis position at two points and record the value of the counts
register at each point. Call the smaller measured position P
0
, and its corresponding
Counts C
0
. Call the greater measured position P
1
, and its corresponding Counts C
1
.
2. Calculate the Position Scale with the following equation:
Position Scale = (P
0
-P
1
)/(C
0
-C
1
)
3. Calculate the Position Offset with the following equation:
Position Offset = P
0
- Position Scale x C
0
Method 2: Using the MDT Calibration Number
1. Obtain the following information (usually from the transducer label or data sheet):
•
Calibration Number (calibration constant) in μs/in or μs/μm (typically about 9
μs/in)
•
Number of Recirculations (if it has no recircs, use a value of 1)
2. Calculate the Position Scale with the following formula:
RMC70:
RMC150:
where
•
"pu" is the position units, e.g. in, mm, m, etc. If you want position units
other than what is given by the Calibration Number (e.g. in,mm, etc.), you
must convert the calibration number to the units you want.
deltamotion.com
17