Delta RMC151 - Manual (Page 34)

RMC70/150 and RMCTools User Manual
The RMC calculates the Actual Position every control-loop time using either of the
following formulas:
Actual Position = (Voltage x Position Scale) + Position Offset
Actual Position = (Current x Position Scale) + Position Offset
Calculating the Position Scale and Offset
The Scale/Offset Wizards provide the easiest method of scaling your axis. If you want to
compute your scale and offset manually, do the following:
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 Volts
register at each point. Call the smaller measured position P
0
, and its corresponding
voltage V
0
or current C
0
. Call the greater measured position P
1
, and its corresponding
voltage V
1
or current C
1
.
2. Calculate the Position Scale with the following equation:
Position Scale = (P
0
-P
1
)/(V
0
-V
1
)
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 V
0
Position Offset = P
0
- Position Scale x C
0
2.2.3. Analog Velocity Scaling
To have any useful meaning, the Voltage or Current from an analog transducer must be scaled
to position or velocity units. This topic describes how to manually calculate the Scaling and
Offset parameters for an analog velocity input.
Delta Recommends using the Scale/Offset Wizard for scaling the velocity. If you need to do it
manually, read this topic.
Scaling Voltage or Current to Velocity Units for Tachometers
The RMC calculates the Actual Velocity from the tachometer voltage every control-loop
time using either of the following formulas:
Actual Velocity = (Voltage + Velocity Offset) x Velocity Scale
Actual Velocity = (Current + Velocity Offset) x Velocity Scale
Calculating the Velocity Scale and Offset
1. From the tachometer specification sheet, determine the voltage or current at which
the velocity is zero. Call it V
ZERO
or C
ZERO
. Or, for greater accuracy, make sure the
tachometer is stopped, then look at the voltage or current feedback value in the
Status Registers pane. Call this value Call it V
ZERO
or C
ZERO
.
2. Negate V
ZERO
or C
ZERO
and enter it as the Velocity Offset:
Velocity Offset = -V
ZERO
Velocity Offset = -C
ZERO
3. From the tachometer specification sheet, determine what the maximum velocity is.
Call it Max Vel.
4. From the tachometer specification sheet, determine what the voltage or current output
should be at the Max Vel. Call it V
MAX
or C
MAX
. Calculate the Velocity Scale with one of
the following equations:
Velocity Scale = Max Vel / (V
MAX
- V
ZERO
)
Velocity Scale = Max Vel / (C
MAX
- C
ZERO
)
1.
14 Delta Computer Systems, Inc.